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Ralph J Volino - One of the best experts on this subject based on the ideXlab platform.
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experimental and computational investigations of separation and transition on a highly loaded low pressure Turbine airfoil part 1 low freestream turbulence intensity
Volume 10: Heat Transfer Fluid Flows and Thermal Systems Parts A B and C, 2008Co-Authors: Mounir B Ibrahim, Olga Kartuzova, Ralph J VolinoAbstract:Boundary layer separation, transition and reattachment have been studied on a very high lift, Low-Pressure Turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 300,000. At the lowest Reynolds number the boundary layer separated and did not reattach, in spite of transition in the separated shear layer. At higher Reynolds numbers the boundary layer did reattach, and the separation bubble became smaller as Re increased. High freestream turbulence increased the thickness of the separated shear layer, resulting in a thinner separation bubble. This effect resulted in reattachment at intermediate Reynolds numbers, which was not observed at the same Re under low freestream turbulence conditions. Numerical simulations were performed using an unsteady Reynolds averaged Navier-Stokes (URANS) code with both a shear stress transport k-ω model and a 4 equation shear stress transport Transition model. Both models correctly predicted separation and reattachment (if it occurred) at all Reynolds numbers. The Transition model generally provided better quantitative results, correctly predicting velocities, pressure, and separation and transition locations. The model also correctly predicted the difference between high and low freestream turbulence cases.Copyright © 2008 by ASME
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separated flow measurements on a highly loaded low pressure Turbine airfoil
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Ralph J VolinoAbstract:Boundary layer separation, transition, and reattachment have been studied on a new, very high lift, Low-Pressure Turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases, the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.
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separated flow transition mechanism and prediction with high and low freestream turbulence under low pressure Turbine conditions
ASME Turbo Expo 2004: Power for Land Sea and Air, 2004Co-Authors: Ralph J Volino, Douglas BohlAbstract:A correlation for separated flow transition has been developed for boundary layers subject to initial acceleration followed by an unfavorable pressure gradient. The correlation is based on the measured growth of small disturbances in the pre-transitional boundary layer. These disturbances were identified and quantified through spectral analysis of the wall normal component of velocity. Cases typical of low pressure Turbine airfoil conditions, with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) were considered at low (0.5%) and high (8.7% inlet) freestream turbulence levels. In some cases, two-dimensional rectangular bars were placed at the beginning of the adverse pressure gradient region as passive flow control devices. The dimensionless magnitude of the initial disturbance which begins to grow at the suction peak depends on the freestream turbulence level and the size of any bar applied to the surface. The growth rate depends on the Reynolds number. When the pre-transitional disturbances grow to a sufficient magnitude, transition begins. The new correlation is based on the physics observed in the turbulence spectra, but allows transition prediction using only the Reynolds number, freestream turbulence level and bar height. The correlation has been checked against experimental data from the literature, and allows transition location prediction to within the uncertainty of the experimental measurements. The correlation represents an improvement over previous correlations which accounted for Reynolds number or freestream turbulence effects, but not both.Copyright © 2004 by ASME
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separation control on low pressure Turbine airfoils using synthetic vortex generator jets
Journal of Turbomachinery-transactions of The Asme, 2003Co-Authors: Ralph J VolinoAbstract:Oscillating vortex generator jets have been used to control boundary layer separation from the suction side of a Low-Pressure Turbine airfoil. A low Reynolds number (Re =25,000) case with low free-stream turbulence has been investigated with detailed measurements including profiles of mean and fluctuating velocity and turbulent shear stress. Ensemble averaged profiles are computed for times within the jet pulsing cycle, and integral parameters and local skin friction coefficients are computed from these profiles. The jets are injected into the mainflow at a compound angle through a spanwise row of holes in the suction surface. Preliminary tests showed that the jets were effective over a wide range of frequencies and amplitudes. Detailed tests were conducted with a maximum blowing ratio of 4. 7 and a dimensionless oscillation frequency of 0.65. The outward pulse from the jets in each oscillation cycle causes a disturbance to move down the airfoil surface. The leading and trailing edge celerities for the disturbance match those expected for a turbulent spot. The disturbance is followed by a calmed region. Following the calmed region, the boundary layer does separate, but the separation bubble remains very thin. Results are compared to an uncontrolled baseline case in which the boundary layer separated and did not reattach, and a case controlled passively with a rectangular bar on the suction surface. The comparison indicates that losses will be substantially lower with the jets than in the baseline or passively controlled cases.
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separation control on low pressure Turbine airfoils using synthetic vortex generator jets
ASME Turbo Expo 2003 collocated with the 2003 International Joint Power Generation Conference, 2003Co-Authors: Ralph J VolinoAbstract:Oscillating vortex generator jets have been used to control boundary layer separation from the suction side of a Low-Pressure Turbine airfoil. A low Reynolds number (Re = 25,000) case with low free-stream turbulence has been investigated with detailed measurements including profiles of mean and fluctuating velocity and turbulent shear stress. Ensemble averaged profiles are computed for times within the jet pulsing cycle, and integral parameters and local skin friction coefficients are computed from these profiles. The jets are injected into the mainflow at a compound angle through a spanwise row of holes in the suction surface. Preliminary tests showed that the jets were effective over a wide range of frequencies and amplitudes. Detailed tests were conducted with a maximum blowing ratio of 4.7 and a dimensionless oscillation frequency of 0.65. The outward pulse from the jets in each oscillation cycle causes a disturbance to move down the airfoil surface. The leading and trailing edge celerities for the disturbance match those expected for a turbulent spot. The disturbance is followed by a calmed region. Following the calmed region, the boundary layer does separate, but the separation bubble remains very thin. Results are compared to an uncontrolled baseline case in which the boundary layer separated and did not reattach, and a case controlled passively with a rectangular bar on the suction surface. The comparison indicates that losses will be substantially lower with the jets than in the baseline or passively controlled cases.Copyright © 2003 by ASME
Rolf Sondergaard - One of the best experts on this subject based on the ideXlab platform.
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R (2005) Designing Low-Pressure Turbine Blades with Integrated Flow Control
2020Co-Authors: Jeffrey P. Bons, John P Clark, Laura C Hansen, Peter J Koch, Rolf SondergaardAbstract:ABSTRACT A low pressure Turbine blade was designed to produce a 17% increase in blade loading over an industry-standard airfoil using integrated flow control to prevent separation. The design was accomplished using two-dimensional CFD predictions of blade performance coupled with insight gleaned from recently published work in transition modeling and from previous experiments with flow control using vortex generator jets (VGJs). In order to mitigate the Reynolds number lapse in efficiency associated with LPT airfoils, a mid-loaded blade was selected. Also, separation predictions from the computations were used to guide the placement of control actuators on the blade suction surface. Three blades were fabricated using the new design and installed in a two-passage linear cascade facility. Flow velocity and surface pressure measurements taken without activating the VGJs indicate a large separation bubble centered at 68% axial chord on the suction surface. The size of the separation and its growth with decreasing Reynolds number agree well with CFD predictions. The separation bubble reattaches to the blade over a wide range of inlet Reynolds numbers from 150,000 down to below 20,000. This represents a marked improvement in separation resistance compared to the original blade profile which separates without reattachment below a Reynolds number of 40,000. This enhanced performance is achieved by increasing the blade spacing while simultaneously adjusting the blade shape to make it less aft-loaded but with a higher peak c p . This reduces the severity of the adverse pressure gradient in the uncovered portion of the modified blade passage. With the use of pulsed VGJs, the design blade loading was achieved while providing attached flow over the entire range of Re. Detailed phaselocked flow measurements using three-component PIV show the trajectory of the jet and its interaction with the unsteady separation bubble. Results illustrate the importance of integrating flow control into the Turbine blade design process and the potential for enhanced Turbine performance
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reynolds number effects on the secondary flow of profile contoured low pressure Turbines
54th AIAA Aerospace Sciences Meeting, 2016Co-Authors: Christopher Marks, Rolf Sondergaard, Philip S Bear, Mitch WolffAbstract:Low pressure Turbine profiles with high aerodynamic loading can suffer from poor midspan performance at lower Reynolds number. Studies have shown that forward loading can mitigate the low Reynolds number lapse in performance at midspan, but concerns remain about increased secondary loss from front loading profiles. The effect of Reynolds number on low pressure Turbine secondary flow losses are considered here. The front loaded L2F profile is studied experimentally in a low speed linear cascade. Several different geometric contours are used to modify the shape of the blade near the endwall, which decreases passage total pressure loss. Profile contouring is accomplished by placing an endwall glove over the blade at the blade to endwall junction. Performance of each profile is compared versus Reynolds number and boundary layer parameters. Translation of dominate secondary loss flow features were tracked using surface oil flow visualization, and their movement in the passage is related to changes in passage total pressure loss. Measurements showed that the lift off-line of the passage vortex moved downstream as Reynolds number decreased, and passage total pressure loss increased.
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secondary flow loss reduction through blowing for a high lift front loaded low pressure Turbine cascade
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, 2012Co-Authors: Stuart I Benton, Jeffrey P. Bons, Rolf SondergaardAbstract:Efforts to increase individual blade loading in the low pressure Turbine have resulted in blade geometries optimized for midspan performance. Many researchers have shown that increased blade loading and a front-loaded pressure distribution each contribute separately to increased losses in the endwall region. A detailed investigation is performed of the baseline endwall flow of the L2F profile, a high-lift, front loaded profile. In-plane velocity vectors and total pressure loss maps are obtained in five planes oriented normal to the blade surface, for three Reynolds numbers. A row of pitched and skewed jets are introduced near the endwall on the suction surface of the blade. The flow control method is evaluated for four momentum coefficients at the high Reynolds number, with a maximum reduction of 42% in the area averaged total pressure loss coefficient. The same blade is also fitted with midspan vortex-generator jets and is tested at a Reynolds number of 20,000, resulting in a 21% reduction in area averaged total pressure loss.Copyright © 2012 by ASME
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secondary flow loss reduction through blowing for a high lift front loaded low pressure Turbine cascade
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, 2012Co-Authors: Stuart I Benton, Jeffrey P. Bons, Rolf SondergaardAbstract:Efforts to increase individual blade loading in the low pressure Turbine have resulted in blade geometries optimized for midspan performance. Many researchers have shown that increased blade loading and a front-loaded pressure distribution each contribute separately to increased losses in the endwall region. A detailed investigation is performed of the baseline endwall flow of the L2F profile, a high-lift, front loaded profile. In-plane velocity vectors and total pressure loss maps are obtained in five planes oriented normal to the blade surface, for three Reynolds numbers. A row of pitched and skewed jets are introduced near the endwall on the suction surface of the blade. The flow control method is evaluated for four momentum coefficients at the high Reynolds number, with a maximum reduction of 42% in the area averaged total pressure loss coefficient. The same blade is also fitted with midspan vortex-generator jets and is tested at a Reynolds number of 20,000, resulting in a 21% reduction in area averaged total pressure loss.Copyright © 2012 by ASME
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an investigation of reynolds lapse rate for highly loaded low pressure Turbine airfoils with forward and aft loading
ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition, 2011Co-Authors: Eric M Lyall, Rolf Sondergaard, Paul I King, John P Clark, Mark McquillingAbstract:This paper presents an experimental and computational study of the midspan low Reynolds number loss behavior for two highly loaded low pressure Turbine airfoils, designated L2F and L2A, which are forward and aft loaded, respectively. Both airfoils were designed with incompressible Zweifel loading coefficients of 1.59. Computational predictions are provided using two codes, Fluent (with k-k1 -ω model) and AFRL’s Turbine Design and Analysis System (TDAAS), each with a different eddy-viscosity RANS based turbulence model with transition capability. Experiments were conducted in a low speed wind tunnel to provide transition models for computational comparisons. The Reynolds number range based on axial chord and inlet velocity was 20,000 < Re < 100,000 with an inlet turbulence intensity of 3.1%. Predictions using TDAAS agreed well with the measured Reynolds lapse rate. Computations using Fluent however, predicted stall to occur at significantly higher Reynolds numbers as compared to experiment. Based on triple sensor hot-film measurements, Fluent’s premature stall behavior is likely the result of the eddy-viscosity hypothesis inadequately capturing anisotropic freestream turbulence effects. Furthermore, rapid distortion theory is considered as a possible analytical tool for studying freestream turbulence that influences transition near the suction surface of LPT airfoils. Comparisons with triple sensor hot-film measurements indicate that the technique is promising but more research is required to confirm its utility.Copyright © 2011 by ASME
Junqiang Zhu - One of the best experts on this subject based on the ideXlab platform.
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unsteady effects of periodic wake passing frequency on aerodynamic performance of ultra high lift low pressure Turbine cascades
Physics of Fluids, 2019Co-Authors: Yanfeng Zhang, Junqiang ZhuAbstract:Flow losses and flow field data downstream of an ultra-high-lift aft-loaded low pressure Turbine cascade were comprehensively measured for different incoming wake passing frequencies, and the mechanisms through which incoming wakes influence secondary flow were examined via numerical calculations. Reynolds numbers ranging from 25 000–100 000 (based on the axial chord and inlet velocity) were considered in both the presence and absence of the wakes. At low Reynolds numbers of 25 000 and 50 000, increasing wake passing frequency gradually suppressed the suction surface separation bubble and increased the cross-passage pressure gradient, and the unsteady wakes clearly improved the throughflow characteristics of the cascade passage. Furthermore, the larger separation bubble on the suction surface hindered the migration of the secondary vortices from the endwall to span. Consequently, incoming wakes were not beneficial for suppressing secondary flow at low Reynolds numbers. At the high Reynolds numbers of 80 000 and 100 000, increasing wake passing frequency afforded stronger inhibition of the secondary flow owing to the reduction in blade loading originating from the “negative jet” influence of the wakes. Transport of incoming wakes in the cascade passage caused the downstream migration of the position of the saddle point, which is also advantageous for decreasing secondary flow losses.Flow losses and flow field data downstream of an ultra-high-lift aft-loaded low pressure Turbine cascade were comprehensively measured for different incoming wake passing frequencies, and the mechanisms through which incoming wakes influence secondary flow were examined via numerical calculations. Reynolds numbers ranging from 25 000–100 000 (based on the axial chord and inlet velocity) were considered in both the presence and absence of the wakes. At low Reynolds numbers of 25 000 and 50 000, increasing wake passing frequency gradually suppressed the suction surface separation bubble and increased the cross-passage pressure gradient, and the unsteady wakes clearly improved the throughflow characteristics of the cascade passage. Furthermore, the larger separation bubble on the suction surface hindered the migration of the secondary vortices from the endwall to span. Consequently, incoming wakes were not beneficial for suppressing secondary flow at low Reynolds numbers. At the high Reynolds numbers of 80 0...
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effect of periodic wakes and a contoured endwall on secondary flow in a high lift low pressure Turbine cascade at low reynolds numbers
Computers & Fluids, 2019Co-Authors: Yanfeng Zhang, Zhijun Lei, Junqiang ZhuAbstract:Abstract The use of a contoured endwall has the potential to suppress endwall secondary flow. Unsteady wakes affect not only the boundary layer characteristics of blade suction surface at blade midspan but also the endwall flow structures. The lack of understanding of the flow mechanism of the combined effects of periodic wakes and contoured endwall on secondary flow limits their roles. This paper presents a experimental and numerical investigation of the endwall secondary flow in a typical high-lift Low-Pressure Turbine cascade. Wakes were produced by moving rods upstream of cascade, and the flow fields at the exit of cascade were measured using a seven-hole pressure probe. The study focused on the combined effect of the upstream wakes and the contoured endwall on the secondary flow as well as the underlying physical mechanisms. The influences of the Reynolds numbers and the contoured endwall on the performance of high-lift Low-Pressure Turbine endwall regions were also discussed. At steady conditions without wakes, the total losses in the Turbine cascade increased with decreasing Reynolds number; the most intense passage vortex, counter vortex and corner vortex were observed at a low Reynolds number of 25,000 (based on the axial chord and the inlet velocity). The contoured endwall decreased the cross-passage pressure gradient, and suppressed the passage vortex. Under unsteady conditions, the interaction between upstream wakes and the passage vortex results in reduction of the passage vortex. The combined effect of the contoured endwall and periodic wakes redistributed the endwall pressure and further decreased the cross-passage pressure gradient. Consequently, the intensities of the passage vortex and counter vortex decreased by 17% and 11% respectively, compared with the flat endwall cascade with wakes. Contoured endwall with wakes reduced secondary kinetic energy of cascade exit by 53.8% than the result of the flat endwall no wake. Which is beneficial to improve the aerodynamic performance of the high-lift Low-Pressure Turbine.
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effects of periodic wakes on the endwall secondary flow in high lift low pressure Turbine cascades at low reynolds numbers
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2019Co-Authors: Yanfeng Zhang, Ge Han, Junqiang ZhuAbstract:Periodic wakes affect not only the surface boundary layer characteristics of Low-Pressure Turbine blades and profile losses but also the vortex structures of the secondary flow and the corresponding losses. Thus, understanding the physical mechanisms of unsteady interactions and the potential to eliminate secondary losses is becoming increasingly important for improving the performance of high-lift Low-Pressure Turbines. However, few studies have focused on the unsteady interaction mechanism between periodic wakes and endwall secondary flow in Low-Pressure Turbines. This paper verified the accuracy of computational fluid dynamics by comparing experimental results and those of the numerical predictions by taking a high-lift Low-Pressure Turbine cascade as the research object. Discussion was focused on the interaction mechanisms between the upstream wakes and secondary flow within the high-lift Low-Pressure Turbine. The results indicated that upstream wakes have both positive and negative effects on the end...
Howard P. Hodson - One of the best experts on this subject based on the ideXlab platform.
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Effects of Reynolds Number and Freestream Turbulence Intensity on the Unsteady Boundary Layer Development on an Ultra-High-Lift Low Pressure Turbine Airfoil
Journal of Turbomachinery, 2009Co-Authors: Xue Feng Zhang, Howard P. HodsonAbstract:The effects of Reynolds numbers and the freestream turbulence intensities (FSTIs) on the unsteady boundary layer development on an ultra-high-lift Low-Pressure Turbine airfoil, so-called T106C, are investigated. The measurements were carried out at both Tu =0.5% and 4.0% within a range of Reynolds numbers, based on the blade chord and the isentropic exit velocity, between 100,000 and 260,000. The interaction between the unsteady wake and the boundary layer depends on both the strength of the wake and the status of the boundary layer. At Tu = 0.5%, both the wake's high turbulence and the negative jet behavior of the wake dominate the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. Since the wake turbulence cannot induce transition before separation on this ultra-high-lift blade, the negative jet of the wake has the opportunity to induce a rollup vortex. At Tu = 4.0%, the time-mean separation on the suction surface is much smaller. With elevated FSTI, the turbulence in the wake just above the boundary layer is no longer distinguishable from the background turbulence level. The unsteady boundary layer transition is dominated by the wake's negative jet induced boundary layer variation.
Lennart Lofdahl - One of the best experts on this subject based on the ideXlab platform.
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numerical validations of secondary flows and loss development downstream of a highly loaded low pressure Turbine outlet guide vane cascade
Proc. of ASME TURBO EXPO 2007 Paper no GT2007-27712, 2007Co-Authors: Johan Hjarne, Valery Chernoray, Jonas Larsson, Lennart LofdahlAbstract:In this paper 3D numerical simulations of turbulent incompressible flows are validated against experimental data from the linear low pressure Turbine/outlet guide vane (LPT/OGV) cascade at Chalmers in Sweden. The validation focuses on the secondary flow-fields and loss developments downstream of a highly loaded OGV. The numerical simulations are performed for the same inlet conditions as in the test-facility with engine-like properties in terms of Reynolds number, boundary-layer thickness and inlet flow angles with the goal to validate how accurately and reliably the secondary flow fields and losses for both on- and off-design conditions can be predicted for OGV’s. Results from three different turbulence models as implemented in FLUENT, k-epsilon Realizable, k-omega-SST and the RSM are validated against detailed measurements. From these results it can be concluded that the RSM model predicts both the secondary flow field and the losses most accurately.
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an experimental investigation of secondary flows and loss development downstream of a highly loaded low pressure Turbine outlet guide vane cascade
ASME Turbo Expo 2006: Power for Land Sea and Air, 2006Co-Authors: Johan Hjarne, Valery Chernoray, Jonas Larsson, Lennart LofdahlAbstract:This paper presents a detailed experimental investigation of the evolution of secondary flow field characteristics and the losses at several measurement planes downstream of a highly loaded low pressure Turbine/outlet guide vane (LPT/OGV). The experiments are conducted in a linear cascade equipped with a boundary-layer suction system designed at Chalmers in Sweden. The aerodynamic function of the LPT/OGV's is to turn the swirling flow out from the last Low-Pressure Turbine rotor into an axial direction. This de-swirling gives a diffusive flow with growing boundary layers, strong secondary flows, and risk for separation both on vanes and end-walls. Important parameters that influence the secondary flow-field are the upstream boundary-layer height, the Re-number and the inlet incidence. All these parameters together with the turbulence intensity can be adjusted in the test-facility in order to encounter engine like conditions. In the final paper several upstream realistic incidences and turbulence intensities are investigated for one Reynolds number. Downstream characteristics have been measured by means of a 5-hole pneumatic probe. It allows for the determination of the mean vortical structures, their development and their interactions. The trailing edge vortices, the two branches of the passage vortex and the corner vortex are clearly visible close to the blade trailing edge. They merge and grow into a single large vortical structure further downstream. Their intensity is shown to be strongly dependent on the incidence. The turbulence level seems to play a role on the mixing inside and between the structures. The measurements also show the dependence of the losses and the mean outlet flow angles along the blade span on the vortices development.
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performance and off design characteristics for low pressure Turbine outlet guide vanes measurements and calculations
2006 ASME 51st Turbo Expo; Barcelona; Spain; 6 May 2006 through 11 May 2006, 2006Co-Authors: Johan Hjarne, Jonas Larsson, Lennart LofdahlAbstract:This paper presents 2D and SD-numerical simulations compared with experimental data from a linear Low Pressure Turbine/Outlet Guide Vane (LPT/OGV) cascade at Chalmers in Sweden. Various performance characteristics for both on and off design cases were investigated, including; pressure distributions, total pressure losses and turning. The numerical simulations were performed with the goal to validate simulation methods and create best-practice guidelines for how to accurately and reliably predict performance and off-design characteristics for an LPT/OGV. The numerical part of the paper presents results using different turbulence models and levels of mesh refinement in order to assess what is the most appropriate simulation approach. From these results it can be concluded that the k-e Realizable model predicts both losses and turning most accurately for both on and off design conditions.
