Endwall Loss and Mixing Analysis of a High Lift Low Pressure Turbine Cascade

A high lift LPT profile designated L2A is used as a test bed for studying the origin of endwall mixing loss and the role of vortical structures in loss development. It is shown analytically and experimentally that the mixing forces within the endwall wake can be decoupled into either mean flow or turbulent forces, and can be further classified as either reversible or irreversible. Among the irreversible forces, mean flow shear is negligible compared to turbulent shear, suggesting that turbulence dissipation is the dominant cause of loss generation. As a result, the mean flow components of the vortical structures do not generate significant mixing losses. Rather than mixing effects, the mean flow of the vortices cause the suction surface boundary layer to separate inside the passage, thereby generating the large low energy regions typical of endwall flows. Losses are generated as the low energy regions mix out. This vortex separation effect is demonstrated with an experiment using a profile fence and pressure surface modification near the endwall. The findings in this paper suggest that profile modifications near the endwall that suppress suction surface separation may provide loss reductions additive to those that weaken vortical structures, such as endwall contouring.

Endwall Loss and Mixing Analysis of a High Lift Low Pressure Turbine Cascade

10.1115/1.4007801 ◽

2013 ◽

Vol 135 (5) ◽

Cited By ~ 6

Author(s):

M. Eric Lyall ◽

Paul I. King ◽

Rolf Sondergaard

Keyword(s):

Low Pressure ◽

Low Energy ◽

Turbulent Shear ◽

Surface Boundary ◽

Test Bed ◽

Mean Flow ◽

High Lift ◽

Vortical Structures ◽

Low Pressure Turbine ◽

A high lift low pressure turbine (LPT) profile designated L2A is used as a test bed for studying the origin of endwall mixing loss and the role of vortical structures in loss development. It is shown analytically and experimentally that the mixing forces within the endwall wake can be decoupled into either mean flow or turbulent forces and can be further classified as either reversible or irreversible. Among the irreversible forces, mean flow shear is negligible compared to turbulent shear, suggesting that turbulence dissipation is the dominant cause of loss generation. As a result, the mean flow components of the vortical structures do not generate significant mixing losses. Rather than mixing effects, the mean flow of the vortices causes the suction surface boundary layer to separate inside the passage, thereby generating the large low energy regions typical of endwall flows. Losses are generated as the low energy regions mix out. This vortex separation effect is demonstrated with an experiment using a profile fence and pressure surface modification near the endwall. The findings in this paper suggest that profile modifications near the endwall that suppress flow separation may provide loss reductions additive to modifications aimed at weakening vortical structures, such as endwall contouring.

Turbulent diffusion near a free surface

Journal of Fluid Mechanics ◽

10.1017/s0022112099007466 ◽

2000 ◽

Vol 407 ◽

pp. 145-166 ◽

Cited By ~ 27

Author(s):

LIAN SHEN ◽

GEORGE S. TRIANTAFYLLOU ◽

DICK K. P. YUE

Keyword(s):

Boundary Layer ◽

Free Surface ◽

Turbulent Diffusion ◽

Similarity Solution ◽

Stokes Equations ◽

Numerical Study ◽

Turbulent Shear ◽

Surface Boundary ◽

Mean Flow ◽

We study numerically and analytically the turbulent diffusion characteristics in a low-Froude-number turbulent shear flow beneath a free surface. In the numerical study, the Navier–Stokes equations are solved directly subject to viscous boundary conditions at the free surface. From an ensemble of such simulations, we find that a boundary layer develops at the free surface characterized by a fast reduction in the value of the eddy viscosity. As the free surface is approached, the magnitude of the mean shear initially increases over the boundary (outer) layer, reaches a maximum and then drops to zero inside a much thinner inner layer. To understand and model this behaviour, we derive an analytical similarity solution for the mean flow. This solution predicts well the shape and the time-scaling behaviour of the mean flow obtained in the direct simulations. The theoretical solution is then used to derive scaling relations for the thickness of the inner and outer layers. Based on this similarity solution, we propose a free-surface function model for large-eddy simulations of free-surface turbulence. This new model correctly accounts for the variations of the Smagorinsky coefficient over the free-surface boundary layer and is validated in both a priori and a posteriori tests.

Boundary Layer Development in the BR710 and BR715 LP Turbines—The Implementation of High-Lift and Ultra-High-Lift Concepts

10.1115/1.1457455 ◽

2002 ◽

Vol 124 (3) ◽

pp. 385-392 ◽

Cited By ~ 43

Author(s):

R. J. Howell ◽

H. P. Hodson ◽

V. Schulte ◽

R. D. Stieger ◽

Heinz-Peter Schiffer ◽

...

Keyword(s):

Boundary Layer ◽

Test Facility ◽

Surface Boundary ◽

Unsteady Boundary Layer ◽

Suction Surface ◽

High Lift ◽

Surface Boundary Layer ◽

Cold Flow ◽

Layer Behavior ◽

Lp Turbine

This paper describes a detailed study into the unsteady boundary layer behavior in two high-lift and one ultra-high-lift Rolls-Royce Deutschland LP turbines. The objectives of the paper are to show that high-lift and ultra-high-lift concepts have been successfully incorporated into the design of these new LP turbine profiles. Measurements from surface mounted hot film sensors were made in full size, cold flow test rigs at the altitude test facility at Stuttgart University. The LP turbine blade profiles are thought to be state of the art in terms of their lift and design philosophy. The two high-lift profiles represent slightly different styles of velocity distribution. The first high-lift profile comes from a two-stage LP turbine (the BR710 cold-flow, high-lift demonstrator rig). The second high-lift profile tested is from a three-stage machine (the BR715 LPT rig). The ultra-high-lift profile measurements come from a redesign of the BR715 LP turbine: this is designated the BR715UHL LP turbine. This ultra-high-lift profile represents a 12 percent reduction in blade numbers compared to the original BR715 turbine. The results from NGV2 on all of the turbines show “classical” unsteady boundary layer behavior. The measurements from NGV3 (of both the BR715 and BR715UHL turbines) are more complicated, but can still be broken down into classical regions of wake-induced transition, natural transition and calming. The wakes from both upstream rotors and NGVs interact in a complicated manner, affecting the suction surface boundary layer of NGV3. This has important implications for the prediction of the flows on blade rows in multistage environments.

Turbulent planar wakes under pressure gradient conditions

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.649 ◽

2017 ◽

Vol 830 ◽

Cited By ~ 4

Author(s):

Sina Shamsoddin ◽

Fernando Porté-Agel

Keyword(s):

Pressure Gradient ◽

Maximum Velocity ◽

Wind Farms ◽

Parameter Tuning ◽

Momentum Equation ◽

Mean Flow ◽

Self Similarity ◽

High Lift ◽

Velocity Deficit ◽

Accurate prediction of the spatial evolution of turbulent wake flows under pressure gradient conditions is required in some engineering applications such as the design of high-lift devices and wind farms over topography. In this paper, we aim to develop an analytical model to predict the evolution of a turbulent planar wake under an arbitrary pressure gradient condition. The model is based on the cross-stream integration of the streamwise momentum equation and uses the self-similarity of the mean flow. We have also made an experimentally supported assumption that the ratio of the maximum velocity deficit to the wake width is independent of the imposed pressure gradient. The asymptotic response of the wake to the pressure gradient is also investigated. After its derivation, the model is successfully validated against experimental data by comparing the evolution of the wake width and maximum velocity deficit. The inputs of the model are the imposed pressure gradient and the wake width under zero pressure gradient. The model does not require any parameter tuning and is deemed to be practical, computationally fast, accurate enough, and therefore useful for the scientific and engineering communities.

Loss reduction on ultra high lift low-pressure turbine blades using selective roughness and wake unsteadiness

The Aeronautical Journal ◽

10.1017/s0001924000004504 ◽

2007 ◽

Vol 111 (1118) ◽

pp. 257-266 ◽

Cited By ~ 1

Author(s):

R. J. Howell ◽

K. M. Roman

Keyword(s):

Boundary Layer ◽

Steady Flow ◽

Separation Bubble ◽

Turbine Blades ◽

Low Pressure ◽

Surface Boundary ◽

Suction Surface ◽

High Lift ◽

Profile Losses ◽

Lp Turbine

This paper describes how it is possible to reduce the profile losses on ultra high lift low pressure (LP) turbine blade profiles with the application of selected surface roughness and wake unsteadiness. Over the past several years, an understanding of wake interactions with the suction surface boundary layer on LP turbines has allowed the design of blades with ever increasing levels of lift. Under steady flow conditions, ultra high lift profiles would have large (and possibly open) separation bubbles present on the suction side which result from the very high diffusion levels. The separation bubble losses produced by it are reduced when unsteady wake flows are present. However, LP turbine blades have now reached a level of loading and diffusion where profile losses can no longer be controlled by wake unsteadiness alone. The ultra high lift profiles investigated here were created by attaching a flap to the trailing edge of another blade in a linear cascade — the so called flap-test technique. The experimental set-up used in this investigation allows for the simulation of upstream wakes by using a moving bar system. Hotwire and hotfilm measurements were used to obtain information about the boundary-layer state on the suction surface of the blade as it evolved in time. Measurements were taken at a Reynolds numbers ranging between 100,000 and 210,000. Two types of ultra high lift profile were investigated; ultra high lift and extended ultra high lift, where the latter has 25% greater back surface diffusion as well as a 12% increase in lift compared to the former. Results revealed that distributed roughness reduced the size of the separation bubble with steady flow. When wakes were present, the distributed roughness amplified disturbances in the boundary layer allowing for more rapid wake induced transition to take place, which tended to eliminate the separation bubble under the wake. The extended ultra high lift profile generated only slightly higher losses than the original ultra high lift profile, but more importantly it generated 12% greater lift.

The Influence of Large-Scale, High-Intensity Turbulence on Vane Aerodynamic Losses, Wake Growth, and the Exit Turbulence Parameters

10.1115/1.2841100 ◽

1997 ◽

Vol 119 (2) ◽

pp. 182-192 ◽

Cited By ~ 29

Author(s):

F. E. Ames ◽

M. W. Plesniak

Keyword(s):

Boundary Layer ◽

High Intensity ◽

Total Pressure ◽

Large Scale ◽

Free Stream ◽

Turbulent Shear ◽

Surface Boundary ◽

Suction Surface ◽

Free Stream Turbulence ◽

Eddy Diffusivities

An experimental research program was undertaken to examine the influence of large-scale high-intensity turbulence on vane exit losses, wake growth, and exit turbulence characteristics. The experiment was conducted in a four-vane linear cascade at an exit Reynolds number of 800,000 based on chord length and an exit Mach number of 0.27. Exit measurements were made for four inlet turbulence conditions including a low-turbulence case (Tu ≈ 1 percent), a grid-generated turbulence case (Tu ≈ 7.5. percent) and two levels of large-scale turbulence generated with a mock combustor (Tu ≈ 12 and 8 percent). Exit total pressure surveys were taken at two locations to quantify total pressure losses. The suction surface boundary layer was also traversed to determine losses due to boundary layer growth. Losses occurred in the core of the flow for the elevated turbulence cases. The elevated free-stream turbulence was found to have a significant effect on wake growth. Generally, the wakes subjected to elevated free-stream turbulence were broader and had smaller peak velocity deficits. Reynolds stress profiles exhibited asymmetry in peak amplitudes about the wake centerline, which are attributable to differences in the evolution of the boundary layers on the pressure and suction surfaces of the vanes. The overall level of turbulence and dissipation inside the wakes and in the free stream was determined to document the rotor inlet boundary conditions. This is useful information for assessing rotor heat transfer and aerodynamics. Eddy diffusivities and mixing lengths were estimated using X-wire measurements of turbulent shear stress. The free-stream turbulence was found to strongly affect eddy diffusivities, and thus wake mixing. At the last measuring position, the average eddy diffusivity in the wake of the high-turbulence close combustor configuration (Tu ≈ 12) was three times that of the low turbulence wake.

A Transport Model for the Deterministic Stresses Associated With Turbomachinery Blade Row Interactions

10.1115/1.1312802 ◽

2000 ◽

Vol 122 (4) ◽

pp. 593-603 ◽

Cited By ~ 23

Author(s):

Allan G. van de Wall ◽

Jaikrishnan R. Kadambi ◽

John J. Adamczyk

Keyword(s):

Turbine Blade ◽

Transport Model ◽

Three Dimensional ◽

Tip Clearance ◽

Two Dimensional ◽

Mean Flow ◽

Viscous Effects ◽

Vortical Structures ◽

Blade Row ◽

The unsteady process resulting from the interaction of upstream vortical structures with a downstream blade row in turbomachines can have a significant impact on the machine efficiency. The upstream vortical structures or disturbances are transported by the mean flow of the downstream blade row, redistributing the time-average unsteady kinetic energy (K) associated with the incoming disturbance. A transport model was developed to take this process into account in the computation of time-averaged multistage turbomachinery flows. The model was applied to compressor and turbine geometry. For compressors, the K associated with upstream two-dimensional wakes and three-dimensional tip clearance flows is reduced as a result of their interaction with a downstream blade row. This reduction results from inviscid effects as well as viscous effects and reduces the loss associated with the upstream disturbance. Any disturbance passing through a compressor blade row results in a smaller loss than if the disturbance was mixed-out prior to entering the blade row. For turbines, the K associated with upstream two-dimensional wakes and three-dimensional tip clearance flows are significantly amplified by inviscid effects as a result of the interaction with a downstream turbine blade row. Viscous effects act to reduce the amplification of the K by inviscid effects but result in a substantial loss. Two-dimensional wakes and three-dimensional tip clearance flows passing through a turbine blade row result in a larger loss than if these disturbances were mixed-out prior to entering the blade row. [S0889-504X(00)01804-3]

Turbulence and Scale Measurements in a Square Channel with Transverse Square Ribs

International Journal of Rotating Machinery ◽

10.1155/s1023621x96000085 ◽

1996 ◽

Vol 2 (3) ◽

pp. 209-218 ◽

Cited By ~ 1

Author(s):

Richard B. Rivir ◽

Mingking K. Chyu ◽

Paul K. Maciejewski

Keyword(s):

Turbulence Intensity ◽

Turbulent Shear ◽

Mean Flow ◽

Integral Scale ◽

Square Channel ◽

Turbulent Shear Layer ◽

The Third ◽

Mainstream Flow ◽

The Mean ◽

Flow Turbulence

Hot-wire measurements of the mean flow, turbulence characteristics, and integral scale in a square channel roughened with transverse ribs mounted on two opposing sidewalls are presented for three rib configurations: single rib, in-line multiple ribs, and staggered multiple ribs. Test conditions for multiple ribs use p/H = 10, H/D 0.17, andRe⁡D23,000. Measured results highlight the spatial distribution and evolution of turbulence intensity and integral scale from the flow entrance of the first period to the developed regime near the exit of the third period. The highly turbulent, shear layer initiated near the trailing upper-edge of a rib elevates the turbulence level in the mainstream of the channel. The magnitude of turbulence intensity in the channel core rises from 0.7% in the approaching flow to about 20–25% near the exit of the third period. The integral scale dominating the mainstream flow increases from approximately one-half the rib-height, 0.5H, in the approaching flow to 1.5-2.5H behind the first rib and further downstream.

The Influence of Large Scale, High Intensity Turbulence on Vane Aerodynamic Losses, Wake Growth, and the Exit Turbulence Parameters

Volume 1: Turbomachinery ◽

10.1115/95-gt-290 ◽

1995 ◽

Cited By ~ 5

Author(s):

Forrest E. Ames ◽

Michael W. Plesniak

Keyword(s):

Boundary Layer ◽

High Intensity ◽

Total Pressure ◽

Large Scale ◽

Free Stream ◽

Turbulent Shear ◽

Surface Boundary ◽

Suction Surface ◽

Free Stream Turbulence ◽

Eddy Diffusivities

An experimental research program was undertaken to examine the influence of large-scale high, intensity turbulence on vane exit losses, wake growth, and exit turbulence characteristics. The experiment was conducted in a four vane linear cascade at an exit Reynolds number of 800, 000 based on chord length and an exit Mach number of 0.27. Exit measurements were made for four inlet turbulence conditions including a low turbulence case (Tu ≈ 1%), a grid-generated turbulence case (Tu ≈ 7.5%), and two levels of large-scale turbulence generated with a mock combustor (Tu ≈ 12% & Tu ≈ 8%). Exit total pressure surveys were taken at two locations to quantify total pressure losses. The suction surface boundary layer was also traversed to determine losses due boundary layer growth. Losses were also found in the core of the flow for the elevated turbulence cases. The elevated free stream turbulence was found to have a significant effect on wake growth. Generally, the wakes subjected to elevated free stream turbulence were broader and had smaller peak velocity deficits. Reynolds stress profiles exhibited asymmetry in peak amplitudes about the wake centerline, which are attributable to differences in the evolution of the boundary layers on the pressure and suction surfaces of the vanes. The overall level of turbulence and dissipation inside the wakes and in the free stream was determined to document the rotor inlet boundary conditions. This is useful information for assessing rotor heat transfer and aerodynamics. Eddy diffusivities and mixing lengths were estimated using X-wire measurements of turbulent shear stress. The free stream turbulence was found to strongly affect eddy diffusivities, and thus wake mixing. At the last measuring position, the average eddy diffusivity in the wake of the high turbulence close combustor configuration (Tu ≈ 12) was three times that of the low turbulence wake.

Stabilization and destabilization of turbulent shear flow in a rotating fluid

Journal of Fluid Mechanics ◽

10.1017/s0022112092002131 ◽

1992 ◽

Vol 241 ◽

pp. 503-523 ◽

Cited By ~ 63

Author(s):

D. J. Tritton

Keyword(s):

Experimental Data ◽

Shear Flow ◽

Reynolds Stress ◽

Rotation Rate ◽

Turbulent Shear ◽

Rotating Fluid ◽

Mean Flow ◽

Rotation Rates ◽

Principal Axes ◽

We consider turbulent shear flows in a rotating fluid, with the rotation axis parallel or antiparallel to the mean flow vorticity. It is already known that rotation such that the shear becomes cyclonic is stabilizing (with reference to the non-rotating case), whereas the opposite rotation is destabilizing for low rotation rates and restabilizing for higher. The arguments leading to and quantifying these statement are heuristic. Their status and limitations require clarification. Also, it is useful to formulate them in ways that permit direct comparison of the underlying concepts with experimental data.An extension of a displaced particle analysis, given by Tritton & Davies (1981) indicates changes with the rotation rate of the orientation of the motion directly generated by the shear/Coriolis instability occurring in the destabilized range.The ‘simplified Reynolds stress equations scheme’, proposed by Johnston, Halleen & Lezius (1972), has been reformulated in terms of two angles, representing the orientation of the principal axes of the Reynolds stress tensor (αa) and the orientation of the Reynolds stress generating processes (αb), that are approximately equal according to the scheme. The scheme necessarily fails at large rotation rates because of internal inconsistency, additional to the fact that it is inapplicable to two-dimensional turbulence. However, it has a wide range of potential applicability, which may be tested with experimental data. αa and αb have been evaluated from numerical data for homogeneous shear flow (Bertoglio 1982) and laboratory data for a wake (Witt & Joubert 1985) and a free shear layer (Bidokhti & Tritton 1992). The trends with varying rotation rate are notably similar for the three cases. There is a significant range of near equality of αa and αb. An extension of the scheme, allowing for evolution of the flow, relates to the observation of energy transfer from the turbulence to the mean flow.