The Experts below are selected from a list of 129 Experts worldwide ranked by ideXlab platform
Hector Iacovides - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of thermal development in a rotating square-ended U-Bend
Experimental Thermal and Fluid Science, 2009Co-Authors: Hector Iacovides, Diamantis KounadisAbstract:This paper reports an experimental study of the thermal development in an idealized model of a blade cooling passage of smooth inner surfaces, comprising a square-ended U-Bend with a cross-section that changes from a square upstream to a 2:1 rectangle downstream of the turn. The two flat walls are heated electrically, while the outer wall and the splitter plate are thermally insulated. The steady state liquid crystal technique is used to map the local Nusselt number variation. Measurements are obtained using a stationary air flow facility and also a rotating water flow facility. This enables us to investigate the effects on the thermal development of the variation in Reynolds from 30,000 to 100,000, in Prandtl number from 0.7 to 5.8 (both for static conditions) and in rotation number, from 0 to 0.4. The effects of minor modifications in the cross-sectional area at the Bend Exit, on the thermal development, under both stationary and rotating conditions, are also explored.
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Experimental Study of the Thermal Development in a Rotating Square-Ended U-Bend
Volume 3: Heat Transfer Parts A and B, 2006Co-Authors: Hector Iacovides, Diamantis Kounadis, Brian LaunderAbstract:This paper reports an experimental study of the thermal development in an idealized model of a blade cooling passage of smooth inner surfaces, comprising a square-ended U-Bend with a cross-section that changes from a square upstream to a 2:1 rectangle downstream of the turn. The two flat walls are heated electrically, while the outer wall and the splitter plate are thermally insulated. The steady state liquid crystal technique is used to map the local Nusselt number variation. Measurements are obtained using a stationary air flow facility and also a rotating water flow facility. This enables us to investigate the effects on the thermal development of Reynolds variation from 30,000 to 100,000, Prandtl numbers of 0.7 and 5.8, and rotation numbers, from 0 to 0.4. The effects of minor modifications in the cross-sectional area at the Bend Exit, on the thermal development, under both stationary and rotating conditions, are also explored.Copyright © 2006 by ASME
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib Roughened Walls
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.Copyright © 1999 by ASME
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib-Roughened Walls
Journal of Turbomachinery, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of the authors recent investigations of convective heat transfer in flow through stationary passages relevant to gas turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross section, with and without artificial wall roughness, are presented. Their earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raises turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs results in a further increase in turbulence levels, a reduction in the size of the curvature-induced separation bubble, and a complex flow development after the Bend Exit with additional separation regions along the outermore » wall. Heat transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat transfer coefficients within the ribbed downstream section are also substantial.« less
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An experimental study of a rib-roughened rotating U-Bend flow
Experimental Thermal and Fluid Science, 1999Co-Authors: Hector Iacovides, D. C. Jackson, Brian Launder, Y M YuanAbstract:Abstract In this paper we report an experimental investigation of turbulent flow through a square-sectioned U-Bend of strong curvature, in which the inner and outer walls of the upstream and downstream sections are artificially roughened with square ribs, in a staggered arrangement. The U-Bend is either stationary or rotates about an axis parallel to that of curvature, with positive rates, i.e. so that the secondary flows provoked by curvature and rotation are in the same sense. The main objective is to provide CFD validation data for flows which contain most of the flow features encountered in blade-cooling passages, but which are numerically easier to compute, while retaining the modelling challenges provided by a real gas-turbine blade. In earlier investigations we showed that the introduction of ribs in the upstream and downstream sections: (a) raises overall turbulence levels; (b) reduces the size of the separation bubble formed along the inner wall of the U-Bend and (c) causes the formation of a large separation bubble along the outer wall, as the flow encounters the first outer-wall rib, after the Bend Exit. Here we: (a) explore how the location of the first outer-wall rib, after the Bend Exit, affects the development of the downstream flow and (b) focus on the three-dimensional character of these flows, by providing data along a plane close to the top (flat) wall, in addition to data along the duct symmetry plane. We show that, for both stationary and rotating conditions, as the first outer-wall rib is moved further away from the Bend Exit, the size of the separation bubble along the outer wall is reduced. The separation bubble along the inner wall, however, increases in size but, overall, turbulence levels are reduced. The flow within and immediately downstream of the U-Bend is highly three-dimensional, showing strong variations from the symmetry plane to the top wall. Rotation generates the expected secondary motion in the straight sections that, at the duct centre, convects the faster fluid towards the pressure side, and along the top and bottom (flat) walls, has the opposite effect. Within and downstream of the Bend, positive rotation reduces the three-dimensionality of the flow.
Brian Launder - One of the best experts on this subject based on the ideXlab platform.
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Experimental Study of the Thermal Development in a Rotating Square-Ended U-Bend
Volume 3: Heat Transfer Parts A and B, 2006Co-Authors: Hector Iacovides, Diamantis Kounadis, Brian LaunderAbstract:This paper reports an experimental study of the thermal development in an idealized model of a blade cooling passage of smooth inner surfaces, comprising a square-ended U-Bend with a cross-section that changes from a square upstream to a 2:1 rectangle downstream of the turn. The two flat walls are heated electrically, while the outer wall and the splitter plate are thermally insulated. The steady state liquid crystal technique is used to map the local Nusselt number variation. Measurements are obtained using a stationary air flow facility and also a rotating water flow facility. This enables us to investigate the effects on the thermal development of Reynolds variation from 30,000 to 100,000, Prandtl numbers of 0.7 and 5.8, and rotation numbers, from 0 to 0.4. The effects of minor modifications in the cross-sectional area at the Bend Exit, on the thermal development, under both stationary and rotating conditions, are also explored.Copyright © 2006 by ASME
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib Roughened Walls
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.Copyright © 1999 by ASME
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib-Roughened Walls
Journal of Turbomachinery, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of the authors recent investigations of convective heat transfer in flow through stationary passages relevant to gas turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross section, with and without artificial wall roughness, are presented. Their earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raises turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs results in a further increase in turbulence levels, a reduction in the size of the curvature-induced separation bubble, and a complex flow development after the Bend Exit with additional separation regions along the outermore » wall. Heat transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat transfer coefficients within the ribbed downstream section are also substantial.« less
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An experimental study of a rib-roughened rotating U-Bend flow
Experimental Thermal and Fluid Science, 1999Co-Authors: Hector Iacovides, D. C. Jackson, Brian Launder, Y M YuanAbstract:Abstract In this paper we report an experimental investigation of turbulent flow through a square-sectioned U-Bend of strong curvature, in which the inner and outer walls of the upstream and downstream sections are artificially roughened with square ribs, in a staggered arrangement. The U-Bend is either stationary or rotates about an axis parallel to that of curvature, with positive rates, i.e. so that the secondary flows provoked by curvature and rotation are in the same sense. The main objective is to provide CFD validation data for flows which contain most of the flow features encountered in blade-cooling passages, but which are numerically easier to compute, while retaining the modelling challenges provided by a real gas-turbine blade. In earlier investigations we showed that the introduction of ribs in the upstream and downstream sections: (a) raises overall turbulence levels; (b) reduces the size of the separation bubble formed along the inner wall of the U-Bend and (c) causes the formation of a large separation bubble along the outer wall, as the flow encounters the first outer-wall rib, after the Bend Exit. Here we: (a) explore how the location of the first outer-wall rib, after the Bend Exit, affects the development of the downstream flow and (b) focus on the three-dimensional character of these flows, by providing data along a plane close to the top (flat) wall, in addition to data along the duct symmetry plane. We show that, for both stationary and rotating conditions, as the first outer-wall rib is moved further away from the Bend Exit, the size of the separation bubble along the outer wall is reduced. The separation bubble along the inner wall, however, increases in size but, overall, turbulence levels are reduced. The flow within and immediately downstream of the U-Bend is highly three-dimensional, showing strong variations from the symmetry plane to the top wall. Rotation generates the expected secondary motion in the straight sections that, at the duct centre, convects the faster fluid towards the pressure side, and along the top and bottom (flat) walls, has the opposite effect. Within and downstream of the Bend, positive rotation reduces the three-dimensionality of the flow.
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The measurement of local wall heat transfer in stationary U-ducts of strong curvate, with smooth and rib roughened walls
Engineering Turbulence Modelling and Experiments 4, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction ofn'bs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.
D. C. Jackson - One of the best experts on this subject based on the ideXlab platform.
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib Roughened Walls
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.Copyright © 1999 by ASME
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib-Roughened Walls
Journal of Turbomachinery, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of the authors recent investigations of convective heat transfer in flow through stationary passages relevant to gas turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross section, with and without artificial wall roughness, are presented. Their earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raises turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs results in a further increase in turbulence levels, a reduction in the size of the curvature-induced separation bubble, and a complex flow development after the Bend Exit with additional separation regions along the outermore » wall. Heat transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat transfer coefficients within the ribbed downstream section are also substantial.« less
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An experimental study of a rib-roughened rotating U-Bend flow
Experimental Thermal and Fluid Science, 1999Co-Authors: Hector Iacovides, D. C. Jackson, Brian Launder, Y M YuanAbstract:Abstract In this paper we report an experimental investigation of turbulent flow through a square-sectioned U-Bend of strong curvature, in which the inner and outer walls of the upstream and downstream sections are artificially roughened with square ribs, in a staggered arrangement. The U-Bend is either stationary or rotates about an axis parallel to that of curvature, with positive rates, i.e. so that the secondary flows provoked by curvature and rotation are in the same sense. The main objective is to provide CFD validation data for flows which contain most of the flow features encountered in blade-cooling passages, but which are numerically easier to compute, while retaining the modelling challenges provided by a real gas-turbine blade. In earlier investigations we showed that the introduction of ribs in the upstream and downstream sections: (a) raises overall turbulence levels; (b) reduces the size of the separation bubble formed along the inner wall of the U-Bend and (c) causes the formation of a large separation bubble along the outer wall, as the flow encounters the first outer-wall rib, after the Bend Exit. Here we: (a) explore how the location of the first outer-wall rib, after the Bend Exit, affects the development of the downstream flow and (b) focus on the three-dimensional character of these flows, by providing data along a plane close to the top (flat) wall, in addition to data along the duct symmetry plane. We show that, for both stationary and rotating conditions, as the first outer-wall rib is moved further away from the Bend Exit, the size of the separation bubble along the outer wall is reduced. The separation bubble along the inner wall, however, increases in size but, overall, turbulence levels are reduced. The flow within and immediately downstream of the U-Bend is highly three-dimensional, showing strong variations from the symmetry plane to the top wall. Rotation generates the expected secondary motion in the straight sections that, at the duct centre, convects the faster fluid towards the pressure side, and along the top and bottom (flat) walls, has the opposite effect. Within and downstream of the Bend, positive rotation reduces the three-dimensionality of the flow.
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The measurement of local wall heat transfer in stationary U-ducts of strong curvate, with smooth and rib roughened walls
Engineering Turbulence Modelling and Experiments 4, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction ofn'bs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.
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LDA Study of the Flow Development Through an Orthogonally Rotating U-Bend of Strong Curvature and Rib-Roughened Walls
Journal of Turbomachinery, 1998Co-Authors: Hector Iacovides, D. C. Jackson, Brian Launder, G. Kelemenis, K. NikasAbstract:This paper reports laser-Doppler anemometry (LDA) and wall pressure measurements of turbulent flow in a square-sectioned, rotating U-Bend, typical of coolant passages employed in modern gas turbine blades. In the upstream and downstream tangents, the pressure and suction (inner and outer) surfaces are roughened with discrete square-sectioned ribs in a staggered arrangement for a rib-height to duct-diameter ratio of 0.1. Three cases have been examined at a passage Reynolds number of 10{sup 5}: a stationary case; a case of positive rotation (the pressure side coinciding with the outer side of the U-Bend) at a rotation Number (Ro {equivalent_to} {Omega}D/U{sub m}) of 0.2; and a case of negative rotation at Ro = {minus}0.2. Measurements have been obtained along the symmetry plane of the duct. In the upstream section, the separation bubble behind each rib is about 2.5 rib heights long. Rotation displaces the high-momentum fluid toward the pressure side, enhances turbulence along the pressure side, and suppresses turbulence along the suction side. The introduction of ribs in the straight sections reduces the size of the separation bubble along the inner wall of the U-Bend, by raising turbulence levels at the Bend entry; it also causes the formation of an additional separationmore » bubble over the first rib interval along the outer wall, downstream of the Bend Exit. Rotation also modifies the mean flow development within the U-Bend, with negative rotation speeding up the flow along the inner wall and causing a wider inner-wall separation bubble at Exit. Turbulence levels within the Bend are generally increased by rotation and, over the first two diameters downstream of the Bend, negative rotation increases turbulence while positive rotation on the whole has the opposite effect.« less
G. Kelemenis - One of the best experts on this subject based on the ideXlab platform.
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib Roughened Walls
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.Copyright © 1999 by ASME
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The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib-Roughened Walls
Journal of Turbomachinery, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of the authors recent investigations of convective heat transfer in flow through stationary passages relevant to gas turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-Bends of square cross section, with and without artificial wall roughness, are presented. Their earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raises turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs results in a further increase in turbulence levels, a reduction in the size of the curvature-induced separation bubble, and a complex flow development after the Bend Exit with additional separation regions along the outermore » wall. Heat transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat transfer coefficients within the ribbed downstream section are also substantial.« less
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The measurement of local wall heat transfer in stationary U-ducts of strong curvate, with smooth and rib roughened walls
Engineering Turbulence Modelling and Experiments 4, 1999Co-Authors: Hector Iacovides, D. C. Jackson, G. Kelemenis, Brian LaunderAbstract:The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. Local Nusselt number measurements in flows through round-ended U-Bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-Bends generate strong secondary motion and cause flow separation at the Bend Exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-Bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the Bend Exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction ofn'bs. The effects of the Bend on the overall levels of Nusselt number are not as strong as in the smooth U-Bend, but are still significant. The effects of the Bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.
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LDA Study of the Flow Development Through an Orthogonally Rotating U-Bend of Strong Curvature and Rib-Roughened Walls
Journal of Turbomachinery, 1998Co-Authors: Hector Iacovides, D. C. Jackson, Brian Launder, G. Kelemenis, K. NikasAbstract:This paper reports laser-Doppler anemometry (LDA) and wall pressure measurements of turbulent flow in a square-sectioned, rotating U-Bend, typical of coolant passages employed in modern gas turbine blades. In the upstream and downstream tangents, the pressure and suction (inner and outer) surfaces are roughened with discrete square-sectioned ribs in a staggered arrangement for a rib-height to duct-diameter ratio of 0.1. Three cases have been examined at a passage Reynolds number of 10{sup 5}: a stationary case; a case of positive rotation (the pressure side coinciding with the outer side of the U-Bend) at a rotation Number (Ro {equivalent_to} {Omega}D/U{sub m}) of 0.2; and a case of negative rotation at Ro = {minus}0.2. Measurements have been obtained along the symmetry plane of the duct. In the upstream section, the separation bubble behind each rib is about 2.5 rib heights long. Rotation displaces the high-momentum fluid toward the pressure side, enhances turbulence along the pressure side, and suppresses turbulence along the suction side. The introduction of ribs in the straight sections reduces the size of the separation bubble along the inner wall of the U-Bend, by raising turbulence levels at the Bend entry; it also causes the formation of an additional separationmore » bubble over the first rib interval along the outer wall, downstream of the Bend Exit. Rotation also modifies the mean flow development within the U-Bend, with negative rotation speeding up the flow along the inner wall and causing a wider inner-wall separation bubble at Exit. Turbulence levels within the Bend are generally increased by rotation and, over the first two diameters downstream of the Bend, negative rotation increases turbulence while positive rotation on the whole has the opposite effect.« less
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LDA Study of the Flow Development Through an Orthogonally Rotating U-Bend of Strong Curvature and Rib Roughened Walls
Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration, 1996Co-Authors: Hector Iacovides, D. C. Jackson, Brian Launder, G. Kelemenis, K. NikasAbstract:This paper reports laser Doppler anemometry (LDA) and wall pressure measurements of turbulent flow in a square-sectioned, rotating U-Bend typical of coolant passages employed in modern gas turbine blades. In the upstream and downstream tangents, the pressure and suction (inner and outer) surfaces are roughened with discrete square-sectioned ribs in a staggered arrangement for a rib-height to duct-diameter ratio of 0.1. Three cases have been examined at a passage Reynolds number of 105: a stationary case; a case of positive rotation (the pressure side coinciding with the outer side of the U-Bend) at a rotation number (Ro=ΩD/Um) of 0.2; and a case of negative rotation at Ro=−0.2. Measurements have been obtained along the symmetry plane of the duct. In the upstream section, the separation bubble behind each rib is about 2.5 rib-heights long. Rotation displaces the high momentum fluid towards the pressure side, enhances turbulence along the pressure side and suppresses turbulence along the suction side. The introduction of ribs in the straight sections reduces the size of the separation bubble along the inner wall of the U-Bend, by raising turbulence levels at the Bend entry; it also causes the formation of an additional separation bubble over the first rib interval along the outer wall, downstream of the Bend Exit. Rotation also modifies the mean flow development within the U-Bend, with negative rotation speeding up the flow along the inner wall and causing a wider inner-wall separation bubble at Exit. Turbulence levels within the Bend are generally increased by rotation and, over the first two diameters downstream of the Bend, negative rotation increases turbulence while positive rotation on the whole has the opposite effect.© 1996 ASME
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Slip velocity and axial dispersion measurements in a gas-solid pipeline using particle tracer analysis
Powder Technology, 1998Co-Authors: Stephen Tallon, Clive E Davies, Bernard J BarryAbstract:Abstract Pulses of radioactive tracer particles were injected into a dilute phase pneumatic conveying system, and their passage along the pipeline was recorded at a number of points. The pipeline incorporated both horizontal and vertical orientations, and horizontal and vertical Bends. Solids slip velocities were calculated from these measurements and showed that the effect of Bends on the solids flow can extend for a long distance downstream of the Bend Exit. The dispersion of the injected pulses along the pipeline is discussed, and dispersion values calculated assuming a simple axial dispersed plug flow model. The results yielded dispersion coefficients higher than those characteristic of turbulent fluid mixing. They also indicated an area about 4 m (50 pipe diameters) downstream from the Exit of two consecutive 90° horizontal Bends where the solids experienced high localised dispersion. This has been attributed to the resuspension of material which continues to flow in strands or ropes for some distance after the Bend Exit.
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Slip Velocity and Axial Dispersion Measurements in a Gas-solids Pipeline Using Particle Tracer Analysis
1996Co-Authors: Stephen Tallon, Clive E Davies, Bernard J BarryAbstract:Pulses of radioactive tracer particles were injected into a dilute phase pneumatic conveying system, and their passage along the pipeline was recorded at a number of points. The pipeline incorporated both horizontal and vertical orientations, and horizontal and vertical Bends. Solids slip velocities calculated from these measurements were significantly higher than the terminal settling velocity of the particles, and showed that the effect of Bends on the solids flow can extend for some distance downstream of the Bend Exit. The dispersion of the injected pulses along the pipeline is discussed, and dispersion values were calculated assuming a simple axial dispersed plug flow model. The results yielded dispersion coefficients higher than those characteristic of turbulent fluid mixing. They also indicated an area about 50 pipe diameters downstream from the Exit of two consecutive 90 horizontal Bends where the solids experienced high localised dispersion. This has been attributed to the re-suspension of material which continues to flow in strands or ropes for some distance out of the Bend.