The Experts below are selected from a list of 78 Experts worldwide ranked by ideXlab platform
Sanjay Chopra - One of the best experts on this subject based on the ideXlab platform.
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Rib-Spacing Effect on Heat Transfer in Rectangular Channels at High Rotation Numbers
Journal of Thermophysics and Heat Transfer, 2009Co-Authors: Sanjay ChopraAbstract:This study experimentally determined the effects of rib spacing on heat transfer in a rotating 1:4 AR channel with a sharp-Bend Entrance. The leading and trailing walls used 45 deg angled ribs. The rib-height-to-hydraulic-diam ratio e/D h was 0.078. The rib-pitch-to-rib-height ratios P/e studied were P/e = 2.5, 5, and 10. Each ratio was tested at five Reynolds numbers up to 40,000. For each Reynolds number, experiments were conducted at five rotational speeds up to 400 rpm. Results showed that the sharp-Bend Entrance has a significant effect on the first-pass heat transfer enhancement. In the second pass, the rib spacing and rotation effect are reduced. The P/e = 10 case had the highest heat transfer enhancement, based on the total area, and the P/e = 2.5 had the highest heat transfer enhancement, based on the projected area. The current study has extended the range of the rotation number Ro and local buoyancy parameter Bo x for a ribbed 1:4 AR channel up to 0.65 and 1.5, respectively. Correlations for predicting heat transfer enhancement due to rotation in the ribbed 1:4 AR channel, based on the extended range of the rotation number and buoyancy parameter, are presented in the paper.
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Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) Under High Rotation Numbers
Journal of Heat Transfer-transactions of The Asme, 2008Co-Authors: Sanjay ChopraAbstract:This paper experimentally investigated the rotational effects on heat transfer in a two-pass rectangular channel (AR = 1: 4), which is applicable to the channel near the leading edge of the gas turbine blade. The test channel has radially outward flow in the first passage through a redirected sharp-Bend Entrance and radially inward flow in the second passage after a 180 deg sharp turn. In the first passage, rotation effects on heat transfer are reduced by the redirected sharp-Bend Entrance. In the second passage, under rotating conditions, both leading and trailing surfaces experienced heat transfer enhancements above the stationary case. Rotation greatly increased heat transfer enhancement in the tip region up to a maximum Nu ratio (Nu/Nu s ) of 2.4. The objective of the current study is to perform an extended parametric study of the low rotation number (0-0.3) and low buoyancy parameter (0-0.2) achieved previously. By varying the Reynolds numbers (10,000-40,000), the rotational speeds (0-400 rpm), and the density ratios (inlet density ratio =0.10-0.16), the increased range of the rotation number and buoyancy parameter reached in this study are 0-0.67 and 0-2.0, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 1:4 aspect ratio flow channel.
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Effect of Rib Spacing on Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) With a Sharp Entrance at High Rotation Numbers
Volume 4: Heat Transfer Parts A and B, 2008Co-Authors: Sanjay ChopraAbstract:The focus of the current study was to determine the effects of rib spacing on heat transfer in rotating 1:4 AR channels. In the current study, heat transfer experiments were performed in a two-pass, 1:4 aspect ratio channel, with a sharp Bend Entrance. The channel leading and trailing walls in the first pass and second pass utilized angled rib turbulators (45° to the mainstream flow). The rib height-to-hydraulic diameter ratio (e/Dh ) was held constant at 0.078. The channel was oriented 90° to the direction of rotation. Three rib pitch-to-rib height ratios (P/e) were studied: P/e = 2.5, 5, and 10. Each ratio was tested at five Reynolds numbers: 10K, 15K, 20K, 30K and 40K. For each Reynolds number, experiments were conducted at five rotational speeds: 0, 100, 200, 300, and 400 rpm. Results showed that the sharp Bend Entrance has a significant effect on the first pass heat transfer enhancement. In the second pass, the rib spacing and rotation effect are reduced. The P/e = 10 case had the highest heat transfer enhancement based on total area, whereas the P/e = 2.5 had the highest heat transfer enhancement based on the projected area. The current study has extended the range of the rotation number (Ro) and local buoyancy parameter (Box ) for a ribbed 1:4 aspect ratio channel up to 0.65 and 1.5, respectively. Correlations for predicting heat transfer enhancement, due to rotation, in the ribbed (P/e = 2.5, 5, and 10) 1:4 aspect ratio channel, based on the extended range of the rotation number and buoyancy parameter, are presented in the paper.Copyright © 2008 by ASME
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Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) Under High Rotation Numbers
Volume 4: Turbo Expo 2007 Parts A and B, 2007Co-Authors: Sanjay ChopraAbstract:This paper experimentally investigated the rotational effects on heat transfer in a two-pass rectangular channel (AR=1:4), which is applicable to the channel near the leading edge of the gas turbine blade. The test channel has radially outward flow in the first passage through a re-directed sharp Bend Entrance and radially inward flow in the second passage after a 180° sharp turn. In the first passage, rotation effects on heat transfer are reduced by the re-directed sharp Bend Entrance. In the second passage, under rotating conditions, both leading and trailing surfaces experienced heat transfer enhancements above the stationary case. Rotation greatly increased heat transfer enhancement in the tip region up to a maximum Nu ratio (Nu/Nus ) of 2.4. The objective of the current study is to perform an extended parameter study of the low rotation number (0–0.3) and low buoyancy parameter (0–0.2) achieved previously. By varying the Reynolds numbers (10000–40000) and the rotational speeds (0–400 rpm), the increased range of the rotation number and buoyancy parameter reached in this study are 0–0.67 and 0–1.9, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 1:4 aspect ratio flow channel.Copyright © 2007 by ASME
J. De Graaff - One of the best experts on this subject based on the ideXlab platform.
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Suspended-load experiments in a curved flume, run no. 6
1991Co-Authors: A.m. Talmon, J. De GraaffAbstract:A laboratory experiment in a 180 degree curved flume with a mobile bed and suspended sediment transport is reported. The flow is steady. The bed topography is measured by means of a profile indicator. Free and forced alternating bars are present. The steady part of the bed topography, which is forced by curvature, is characterized by a below critical response of the transverse bed slope. Downstream of the Bend Entrance overdeepening occurs, this is repeated with a somewhat smaller amplitude further downstream. Suspended sediment concentrations are measured.
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Suspended-load experiments in a curved flume, run no. 5
1991Co-Authors: A.m. Talmon, J. De GraaffAbstract:A laboratory experiment in a 180 degree curved flume with a mobile bed and suspended sediment transport is reported. The flow is steady. The bed topography is measured by means of a profile indicator. Free and forced alternating bars are present. The steady part of the bed topography, which is forced by curvature, is characterized by a below critical response of the transverse bed slope. Downstream of the Bend Entrance overdeepening occurs, this is weakly repeated further downstream, at these location the transverse bed slope is maximal. Further downstream the transverse bed slope decreases and converges to an approximately constant slope (constant in main flow direction). Suspended sediment concentrations are measured.
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Suspended-load experiments in a curved flume, run no. 4
1990Co-Authors: A.m. Talmon, J. De GraaffAbstract:A laboratory experiment in a 180 degree curved flume with a mobile bed and suspended sediment transport is described. The flow is steady. The median sediment diameter (160 micrometer) is larger than in the preceeding experiments, run no. 1 to 3 (90 micrometer). The bed topography is measured by means of a profile indicator. The bed topography is characterized by a slowly damped oscillation of the transverse bed slope. Downstream of the Bend Entrance a pool and a submerged point-bar are present, here the radial bed slope is maximal. Further downstream the transverse bed slope decreases and converges to a constant slope (constant in main flow direction), here the bed topography is axi-symmetrical. The topography resembles that of run no. 2 but has a more pronounced axi-symmetrical region. Suspended sediment concentrations are determined by the method of siphoning and by optical measurement. In the region of axi-symmetrical bed topography a dense measuring grid is employed.
R. M. C. So - One of the best experts on this subject based on the ideXlab platform.
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Swirling turbulent flow through a curved pipe
Experiments in Fluids, 1993Co-Authors: M. Anwer, R. M. C. SoAbstract:An experimental study of a swirling turbulent flow through a curved pipe with a pipe-to-mean-Bend radius ratio of 0.077 and a flow Reynolds number based on pipe diameter and mean bulk velocity of 50,000 has been carried out. A rotating section, six pipe diameters long, is set up at six diameters upstream of the curved Bend Entrance. The rotating section is designed to provide a solid-body rotation to the flow. At the Entrance of the rotating section, a fully-developed turbulent pipe flow is established. This study reports on the flow characteristics for the case where the swirl number, defined as the ratio of the pipe circumferential velocity to mean bulk velocity, is one. Wall static pressures, mean velocities, Reynolds stresses and wall shear distribution around the pipe are measured using pressure transducers, rotating-wires and surface hot-film gauges. The measurements are used to analyze the competing effects of swirl and Bend curvature on curved-pipe flows, particularly their influence on the secondary flow pattern in the crossstream plane of the curved pipe. At this swirl number, all measured data indicate that, besides the decaying combined free and forced vortex, there are no secondary cells present in the cross-stream plane of the curved pipe. Consequently, the flow displays characteristics of axial symmetry and the turbulent normal stress distributions are more uniform across the pipe compared to fully-developed pipe flows.
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Swirling turbulent flow through a curved pipe Part 2: Recovery from swirl and Bend curvature
Experiments in Fluids, 1993Co-Authors: R. M. C. So, M. AnwerAbstract:An experimental study of swirling turbulent flow through a curved Bend and its downstream tangent has been carried out. This study reports on the recovery from swirl and Bend curvature and relies on measurements obtained in the downstream tangent and data reported in Part 1 to assess the recovery. Unlike the non- swirling flow case, the present measurements show that the cross- stream secondary flow is dominated by the decay of the solid-body rotation and the total wall shear stress measured at the inner and outer Bend (furthest away from the Bend center of curvature) is approximately equal. The shear distribution is fairly uniform, even at 1 D downstream of the Bend exit. At 49 D downstream of the Bend exit, the mean axial velocity has recovered to its measured profile at 18 D upstream of the Bend Entrance. Furthermore, the mean tangen- tial velocity is close to zero everywhere and the turbulent shear and normal stresses take another 15 D to approximately approach their stationary straight pipe values. Therefore, complete flow recovery from swirl and Bend curvature takes a total length of about 85D from the Bend Entrance. This compares with a recovery length of about 78 D for Bend curvature alone. The recovery length is substan- tially shorter than that measured previously in swirling flow through straight pipes and is a consequence of the angular momen- tum decreasing by approximately 74% across the curved Bend. Consequently, the effect of Bend curvature is to accelerate swirl decay in a pipe flow. List of symbols
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Swirling turbulent flow through a curved pipe
Experiments in Fluids, 1993Co-Authors: R. M. C. So, M. AnwerAbstract:An experimental study of swirling turbulent flow through a curved Bend and its downstream tangent has been carried out. This study reports on the recovery from swirl and Bend curvature and relies on measurements obtained in the downstream tangent and data reported in Part 1 to assess the recovery. Unlike the nonswirling flow case, the present measurements show that the cross-stream secondary flow is dominated by the decay of the solid-body rotation and the total wall shear stress measured at the inner and outer Bend (furthest away from the Bend center of curvature) is approximately equal. The shear distribution is fairly uniform, even at 1 D downstream of the Bend exit. At 49D downstream of the Bend exit, the mean axial velocity has recovered to its measured profile at 18D upstream of the Bend Entrance. Furthermore, the mean tangential velocity is close to zero everywhere and the turbulent shear and normal stresses take another 15D to approximately approach their stationary straight pipe values. Therefore, complete flow recovery from swirl and Bend curvature takes a total length of about 85D from the Bend Entrance. This compares with a recovery length of about 78D for Bend curvature alone. The recovery length is substantially shorter than that measured previously in swirling flow through straight pipes and is a consequence of the angular momentum decreasing by approximately 74% across the curved Bend. Consequently, the effect of Bend curvature is to accelerate swirl decay in a pipe flow.
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Turbulence-driven secondary flows in a curved pipe
Theoretical and Computational Fluid Dynamics, 1991Co-Authors: R. M. C. So, H. S. ZhangAbstract:If the torque exerted on a fluid element and the source of streamwise vorticity generation are analyzed, a turbulence-driven secondary flow is found to be possible in a curved pipe. Based on this analysis, it is found that the secondary flow is primarily induced by high anisotropy of the cross-stream turbulent normal stresses near the outer Bend (furthest from the center of curvature of the Bend). This secondary flow appears as a counterrotating vortex pair embedded in a Dean-type secondary motion. Recent hot-wire measurements provide some evidence for the existence of this vortex pair. To verify the formation and extent of this turbulence-driven vortex pair further, a near-wall Reynolds-stress model is used to carry out a detailed numerical investigation of a curved-pipe flow. The computation is performed specifically for a U -Bend with a full developed turbulent flow at the Bend Entrance and a long straight pipe attached to the exit. Numerical results reveal that there are three vortex pairs in a curved pipe. The primary one is the Dean-type vortex pair. Another pair exists near the pipe core and is a consequence of local pressure imbalance. A third pair is found near the outer Bend and is the turbulence-driven secondary flow. It starts to appear around 60° from the Bend Entrance, grows to a maximum strength at the Bend exit, and disappears altogether at about seven pipe diameters downstream of the Bend. On the other hand, calculations of developing laminar curved-pipe flows covering a range of pipe-to-Bend curvature ratios, Reynolds number, and different inlet conditions fail to give rise to a third cell near the outer Bend. Therefore, experimental and numerical evidence together lend support to the formation of a pair of turbulence-driven secondary cells in curved-pipe flows.
M. Anwer - One of the best experts on this subject based on the ideXlab platform.
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Swirling turbulent flow through a curved pipe
Experiments in Fluids, 1993Co-Authors: M. Anwer, R. M. C. SoAbstract:An experimental study of a swirling turbulent flow through a curved pipe with a pipe-to-mean-Bend radius ratio of 0.077 and a flow Reynolds number based on pipe diameter and mean bulk velocity of 50,000 has been carried out. A rotating section, six pipe diameters long, is set up at six diameters upstream of the curved Bend Entrance. The rotating section is designed to provide a solid-body rotation to the flow. At the Entrance of the rotating section, a fully-developed turbulent pipe flow is established. This study reports on the flow characteristics for the case where the swirl number, defined as the ratio of the pipe circumferential velocity to mean bulk velocity, is one. Wall static pressures, mean velocities, Reynolds stresses and wall shear distribution around the pipe are measured using pressure transducers, rotating-wires and surface hot-film gauges. The measurements are used to analyze the competing effects of swirl and Bend curvature on curved-pipe flows, particularly their influence on the secondary flow pattern in the crossstream plane of the curved pipe. At this swirl number, all measured data indicate that, besides the decaying combined free and forced vortex, there are no secondary cells present in the cross-stream plane of the curved pipe. Consequently, the flow displays characteristics of axial symmetry and the turbulent normal stress distributions are more uniform across the pipe compared to fully-developed pipe flows.
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Swirling turbulent flow through a curved pipe Part 2: Recovery from swirl and Bend curvature
Experiments in Fluids, 1993Co-Authors: R. M. C. So, M. AnwerAbstract:An experimental study of swirling turbulent flow through a curved Bend and its downstream tangent has been carried out. This study reports on the recovery from swirl and Bend curvature and relies on measurements obtained in the downstream tangent and data reported in Part 1 to assess the recovery. Unlike the non- swirling flow case, the present measurements show that the cross- stream secondary flow is dominated by the decay of the solid-body rotation and the total wall shear stress measured at the inner and outer Bend (furthest away from the Bend center of curvature) is approximately equal. The shear distribution is fairly uniform, even at 1 D downstream of the Bend exit. At 49 D downstream of the Bend exit, the mean axial velocity has recovered to its measured profile at 18 D upstream of the Bend Entrance. Furthermore, the mean tangen- tial velocity is close to zero everywhere and the turbulent shear and normal stresses take another 15 D to approximately approach their stationary straight pipe values. Therefore, complete flow recovery from swirl and Bend curvature takes a total length of about 85D from the Bend Entrance. This compares with a recovery length of about 78 D for Bend curvature alone. The recovery length is substan- tially shorter than that measured previously in swirling flow through straight pipes and is a consequence of the angular momen- tum decreasing by approximately 74% across the curved Bend. Consequently, the effect of Bend curvature is to accelerate swirl decay in a pipe flow. List of symbols
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Swirling turbulent flow through a curved pipe
Experiments in Fluids, 1993Co-Authors: R. M. C. So, M. AnwerAbstract:An experimental study of swirling turbulent flow through a curved Bend and its downstream tangent has been carried out. This study reports on the recovery from swirl and Bend curvature and relies on measurements obtained in the downstream tangent and data reported in Part 1 to assess the recovery. Unlike the nonswirling flow case, the present measurements show that the cross-stream secondary flow is dominated by the decay of the solid-body rotation and the total wall shear stress measured at the inner and outer Bend (furthest away from the Bend center of curvature) is approximately equal. The shear distribution is fairly uniform, even at 1 D downstream of the Bend exit. At 49D downstream of the Bend exit, the mean axial velocity has recovered to its measured profile at 18D upstream of the Bend Entrance. Furthermore, the mean tangential velocity is close to zero everywhere and the turbulent shear and normal stresses take another 15D to approximately approach their stationary straight pipe values. Therefore, complete flow recovery from swirl and Bend curvature takes a total length of about 85D from the Bend Entrance. This compares with a recovery length of about 78D for Bend curvature alone. The recovery length is substantially shorter than that measured previously in swirling flow through straight pipes and is a consequence of the angular momentum decreasing by approximately 74% across the curved Bend. Consequently, the effect of Bend curvature is to accelerate swirl decay in a pipe flow.
Sumanta Acharya - One of the best experts on this subject based on the ideXlab platform.
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Effect of Entrance Geometry and Rotation on Heat Transfer in a Narrow (AR=1:4) Rectangular Internal Cooling Channel
Volume 5A: Heat Transfer, 2014Co-Authors: Krishnendu Saha, Sumanta AcharyaAbstract:This paper studies the effect of Entrance geometries on the heat transfer and fluid flow in a narrow aspect ratio (AR = 1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade, under rotating condition. Numerical simulations are performed to understand the role of the rotation generated forces on the flow for different Entrance geometries representative of those encountered in practice. Three different Entrance geometries are tested: a S-shape Entrance, a 90 degree Bend Entrance and a twisted Entrance that changes its aspect ratio along its length. Numerical simulations are run at a constant Reynolds number (Re = 15000), for a range of rotation numbers (Ro = 0–0.2) and density ratios (DR = 0–0.4). Detailed heat transfer coefficient data at the leading and trailing walls are presented along with streamline profiles at different cross sectional planes that provide an insight into the flow field. It is seen that the Entrance profile upstream of the actual test section is significantly different for the different Entrance geometries, and has a significant impact on the rotation generated secondary flows. Non-uniformity in flow distribution at the exit of Entrance geometry is small for the S-shape Entrance while the non-uniformity is prominent at the exit of the changing AR Entrance geometry. The Entrance effect dies down as the flow progresses further downstream inside the cooling channel and the rotation effect becomes dominant.Copyright © 2014 by ASME
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Effect of Entrance Geometry on Heat Transfer in a Narrow (AR=1:4) Rectangular Two Pass Channel With Smooth and Ribbed Walls
Volume 5: Heat Transfer Parts A and B, 2011Co-Authors: Krishnendu Saha, Sumanta AcharyaAbstract:This paper studies the effect of Entrance geometries on the heat transfer in a narrow aspect ratio (AR=1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade. Detailed heat transfer coefficient distributions are measured for three different Entrance geometries: S-shape Entrance, 90 degree Bend Entrance and a twisted Entrance with changing AR. Both smooth and ribbed channels are used in a two pass channel configuration. A baseline straight-entry channel is used as a reference for comparison. The tests are done for Reynolds number ranging from 15000 to 55000. The ribs are placed at an angle of 45° to the mainstream flow. The results show that the effects of Entrance geometry persist throughout the first pass (up to a distance of 9 times the hydraulic diameter) for the smooth channel. All the Entrance geometries provided enhancement in heat transfer compared to the straight fully developed Entrance, with the 90 degree Bend Entrance providing the highest enhancement. The effect of Entrance is less pronounced for the ribbed test section case with the effects confined more in the early developing regions. The 90 degree Bend Entrance and the twisted-entry cases enhance heat transfer for the ribbed test section, while the S-shape Entrance reduces the heat transfer for the ribbed test section relative to the straight entry channel.Copyright © 2011 by ASME
