Investigation of Boundary Layer Transition and Separation in an Axial Turbine Cascade Using Glue-On Hot-Film Gages

1988 ◽  
Author(s):  
S. B. Vijayaraghavan ◽  
P. Kavanagh
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Boundary Layer Transition ◽  
Surface Boundary ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Layer Transition ◽  
Axial Turbine ◽  
Free Stream Turbulence ◽  
Hot Film

Experiments were conducted with glue-on hot-film gages in a large-scale axial turbine cascade to identify transition and/or separation on the suction surface of the blade. Standard strain-gage type temperature sensors were adapted and used as the gages and Transition and separation were identified by examining the mean and RMS voltage output. To assist with interpreting the output of the gages, surface oil-flow visualizations were used. Results of this study showed that transition and separation could be easily identified with the hot-film gages. Depending upon the Reynolds number and free stream turbulence level, the suction surface boundary layer was found to undergo bubble-induced transition, natural transition, or a combination of both; i.e, a transition which started naturally but ended abruptly with a bubble.

Unsteady Transition in an Axial-Flow Turbine: Part 1—Measurements on the Turbine Rotor

1990 ◽  
Vol 112 (2) ◽  
pp. 206-214 ◽  
Author(s):  
J. S. Addison ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Cross Sections ◽  
Axial Flow ◽  
Transition Process ◽  
Turbine Rotor ◽  
Boundary Layer Transition ◽  
Surface Boundary ◽  
Suction Surface ◽  
Layer Transition ◽  
Time Resolved

Previously published measurements in a low-speed, single-stage, axial-flow turbine have been reanalyzed in the light of more recent understanding. The measurements include time-resolved hot-wire traverses and surface hot film gage measurements at the midspan of the rotor suction surface with three different rotor-stator spacings. Part 1 investigates the suction surface boundary layer transition process, using surface-distance time plots and boundary layer cross sections to demonstrate the unsteady and two-dimensional nature of the process. Part 2 of the paper will describe the results of supporting experiments carried out in a linear cascade together with a simple transition model, which explains the features seen in the turbine.

The Influence of Turbulence on Wake Dispersion and Blade Row Interaction in an Axial Compressor

2005 ◽  
Author(s):  
Alan D. Henderson ◽  
Gregory J. Walker ◽  
Jeremy D. Hughes
Keyword(s):  
Boundary Layer ◽  
Guide Vane ◽  
Axial Compressor ◽  
Boundary Layer Transition ◽  
Inlet Guide Vane ◽  
Grid Turbulence ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Hot Film ◽  
Blade Element

The influence of free-stream turbulence on wake dispersion and boundary layer transition processes has been studied in a 1.5-stage axial compressor. An inlet grid was used to produce turbulence characteristics typical of an embedded stage in a multistage machine. The grid turbulence strongly enhanced the dispersion of inlet guide vane (IGV) wakes. This modified the interaction of IGV and rotor wakes, leading to a significant decrease in periodic unsteadiness experienced by the downstream stator. These observations have important implications for the prediction of clocking effects in multistage machines. Boundary layer transition characteristics on the outlet stator were studied with a surface hot-film array. Observations with grid turbulence were compared with those for the natural low turbulence inflow to the machine. The transition behavior under low turbulence inflow conditions with the stator blade element immersed in the dispersed IGV wakes closely resembled the behavior with elevated grid turbulence. It is concluded that with appropriate alignment, the blade element behavior in a 1.5-stage axial machine can reliably indicate the blade element behavior of an embedded row in a multistage machine.

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

1997 ◽  
Vol 119 (2) ◽  
pp. 182-192 ◽  
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 new boundary layer wind tunnel

1988 ◽  
Vol 92 (916) ◽  
pp. 224-229
Author(s):  
P. E. Roach
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Test Section ◽  
Gas Turbines ◽  
Large Scale ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Dimensional Boundary

Summary The procedures employed for the design of a closed-circuit, boundary layer wind tunnel are described. The tunnel was designed for the generation of relatively large-scale, two-dimensional boundary layers with Reynolds numbers, pressure gradients and free-stream turbulence levels typical of the turbomachinery environment. The results of a series of tests to evaluate the tunnel performance are also described. The flow in the test section is shown to be highly uniform and steady, with very low (natural) free-stream turbulence intensities. Measured boundary layer mean and fluctuating velocity profiles were found to be in good agreement with classical correlations. Test-section free-stream turbulence intensities are presented for grid-generated turbulence: agreement with expectation is again found to be good. Immediate applications to the tunnel include friction drag reduction and boundary layer transition studies, with future possibilities including flow separation and other complex flows typical of those found in gas turbines.

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

1995 ◽  
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.

Large Eddy Simulation of Periodic Wake Impact on Boundary Layer Transition Mechanisms on a Highly Loaded Low-Pressure Turbine Blade

2020 ◽  
Author(s):  
Benjamin Winhart ◽  
Martin Sinkwitz ◽  
Andreas Schramm ◽  
Pascal Post ◽  
Francesca di Mare
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Array Measurements ◽  
Numerical Predictions ◽  
Large Eddy ◽  
Highly Loaded

Abstract In the proposed paper the transient interaction between periodic incoming wakes and the laminar separation bubble located on the rear suction surface of a typical, highly loaded LPT blade is investigated by means of highly resolved large-eddy simulations. An annular, large scale, 1.5-stage LPT test-rig, equipped with a modified T106 turbine blading and an upstream rotating vortex generator is considered and the numerical predictions are compared against hot film array measurements. In order to accurately assess both baseline transition and wake impact, simulations were conducted with unperturbed and periodically perturbed inflow conditions. Main mechanisms of transition and wake-boundary layer interaction are investigated utilizing a frequency-time domain analysis. Finally visualizations of the main flow structures and shear layer instabilities are provided utilizing the q-criterion as well as the finite-time Lyapunov exponent.

Numerical Investigation of Three-Dimensional Separation in an Axial Flow Compressor: The Influence of Free-Stream Turbulence Intensity and Endwall Boundary Layer State

2016 ◽  
Author(s):  
Ashley D. Scillitoe ◽  
Paul G. Tucker ◽  
Paolo Adami
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Boundary Layer Transition ◽  
Surface Boundary ◽  
Suction Surface ◽  
Corner Separation ◽  
Free Stream Turbulence

Regions of three-dimensional separations are an inherent flow feature of the suction surface - endwall corner in axial compressors. These corner separations can cause a significant total pressure loss and reduce the compressor’s efficiency. This paper uses wall-resolved LES to investigate the loss sources in a corner separation, and examines the influence of the inflow turbulence on these sources. Different subgrid scale (SGS) models are tested and the choice of model is found to be important. The σ SGS model, which performed well, is then used to perform LES of a compressor endwall flow. The time-averaged data is in good agreement with measurements. The viscous and turbulent dissipation are used to highlight the sources of loss, with the latter being dominant. The key loss sources are seen to be the 2D laminar separation bubble and trailing edge wake, and the 3D flow region near the endwall. Increasing the free-stream turbulence intensity (FST) changes the suction surface boundary layer transition mode from separation induced to bypass. However, it doesn’t significantly alter the transition location and therefore the corner separation size. Additionally, the FST doesn’t noticeably interact with the corner separation itself, meaning that in this case the corner separation is relatively insensitive to the FST. The endwall boundary layer state is found to be significant. A laminar endwall boundary layer separates much earlier leading to a larger passage vortex. This significantly alters the endwall flow and loss. Hence, the need for accurate boundary measurements is clear.

The Influence of Turbulence on Wake Dispersion and Blade Row Interaction in an Axial Compressor

2005 ◽  
Vol 128 (1) ◽  
pp. 150-157 ◽  
Author(s):  
Alan D. Henderson ◽  
Gregory J. Walker ◽  
Jeremy D. Hughes
Keyword(s):  
Boundary Layer ◽  
Guide Vane ◽  
Axial Compressor ◽  
Boundary Layer Transition ◽  
Inlet Guide Vane ◽  
Grid Turbulence ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Hot Film ◽  
Blade Element

The influence of free-stream turbulence on wake dispersion and boundary layer transition processes has been studied in a 1.5-stage axial compressor. An inlet grid was used to produce turbulence characteristics typical of an embedded stage in a multistage machine. The grid turbulence strongly enhanced the dispersion of inlet guide vane (IGV) wakes. This modified the interaction of IGV and rotor wakes, leading to a significant decrease in periodic unsteadiness experienced by the downstream stator. These observations have important implications for the prediction of clocking effects in multistage machines. Boundary layer transition characteristics on the outlet stator were studied with a surface hot-film array. Observations with grid turbulence were compared with those for the natural low turbulence inflow to the machine. The transition behavior under low turbulence inflow conditions with the stator blade element immersed in the dispersed IGV wakes closely resembled the behavior with elevated grid turbulence. It is concluded that with appropriate alignment, the blade element behavior in a 1.5-stage axial machine can reliably indicate the blade element behavior of an embedded row in a multistage machine.

Large Eddy Simulation of a Transonic Linear Cascade With Synthetic Inlet Turbulence

2020 ◽  
Author(s):  
Ettore Bertolini ◽  
Paul Pieringer ◽  
Wolfgang Sanz
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Boundary Layer Transition ◽  
Turbine Cascade ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Turbulence Decay ◽  
Large Eddy

Abstract The aim of this work is to predict the boundary layer transition and the heat transfer on a highly loaded transonic turbine cascade using Large Eddy Simulations (LESs) with prescribed inlet synthetic turbulence. The numerical simulations were performed for the flow in a linear turbine cascade tested at the von Karman Institute for Fluid Dynamic (MUR test case). For the numerical case, two operating conditions with two different levels of free-stream turbulence intensity are evaluated. For the lower turbulence level case (Tu = 0.8%, MUR132) a laminar inflow is used for the LES simulations whereas for the higher one (Tu = 6%, MUR237) the inlet turbulence is prescribed by using the Synthetic Eddy Method (SEM) of Jarrin. The first part of this work deals with the LES setup. The standard Smagorinsky model was used as closure model. A value of the Smagorinsky constant CS = 0.05 was chosen whereas the turbulent viscosity was reduced in the region closest to the wall by changing the definition of the Smagorinsky length scale. To handle the strong fluctuations in the flow field the cell fluxes are computed using the WENO-P scheme. In the second part, precursor RANS and LES simulations are used to set the optimal values of the SEM parameters and to guarantee the correct level of turbulence at the blade leading edge. The turbulence decay of the synthetic turbulence is compared with the one of the RANS κ–ωSST model. Finally, a comparison between experimental and numerical results is done and the ability of LES to predict the boundary layer transition and the heat transfer on the blade surface is evaluated for the two different inflow conditions.

scholarly journals Effect of Free-Stream Turbulence, Reynolds Number, and Incidence on Axial Turbine Cascade Performance

1988 ◽  
Author(s):  
S. B. Vijayaraghavan ◽  
P. Kavanagh
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Incidence Angle ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Axial Turbine ◽  
Free Stream Turbulence ◽  
Oil Flow ◽  
Two Dimensional Flow

A large-scale, low-speed, axial turbine cascade designed for high-loading and high-turning was tested over a range of Reynolds number, turbulence level, and incidence angle. End wall suction was applied to provide two-dimensional flow over a large spanwise region of the airfoil. In all, thirty-six test conditions were examined. Overall cascade performance including mass-averaged loss coefficients at each test flow condition was determined from detailed five-hole pressure probe traverses in an exit plane of the cascade. In addition, using glue-on hot-film gages and surface oil-flow visualizations, transition and/or separation was identified over the suction surface of the airfoil. The measured transition start and end points were compared against predictions using existing transition models. Also, the measured losses were compared against predicted losses from boundary layer calculations based on finite difference analysis.

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