Separation and Relaminarization at the Circular Arc Leading Edge of a Controlled Diffusion Compressor Stator

2012 ◽  
Author(s):  
Samuel C. T. Perkins ◽  
Alan D. Henderson
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Leading Edge ◽  
Suction Surface ◽  
Circular Arc ◽  
Controlled Diffusion ◽  
Boundary Layer Development ◽  
Layer Development

This paper investigates the influence of Reynolds Number and incidence on boundary layer development at the leading edge of a controlled diffusion (CD) stator blade with circular arc leading edge profile. Steady flow measurements were made inside a large scale 2D compressor cascade at Reynolds numbers of 260,000 and 400,000 for a range of inlet flow angles corresponding to both positive and negative incidence. Detailed static pressure measurements in the leading edge region show the time-mean boundary layer development through the velocity overspeed and following region of accelerating flow on the suction surface. Separation bubbles at the leading edge of the pressure and suction surfaces trigger the boundary layer to undergo an initial and rapid transition to turbulence. On the pressure surface, the bubble forms at all values of incidence tested, whereas on the suction surface a bubble only forms for incidence greater than design. In all cases the bubble length was seen to reduce significantly as Reynolds number is increased. These trends are supported by surface flow visualization results. Quasi-wall shear stress measurements from hot-film sensors were interpreted using a hybrid threshold peak-valley-counting algorithm to yield time-averaged turbulent intermittency on each blade surface. These results in combination with raw quasi-wall shear stress traces show evidence of boundary layer relaminarization on the suction surface, downstream of the leading edge velocity overspeed in the favorable pressure gradient leading to peak suction. The relaminarization process is observed to become less effective as Reynolds number and inlet flow angle are increased. The boundary layer development is shown to have a large influence on the total blade pressure loss. At negative incidence, loss was seen to increase as Reynolds number is decreased, and in contrast at positive incidence, the opposite trend was displayed.

Observations of Transition Phenomena on a Controlled Diffusion Compressor Stator With a Circular Arc Leading Edge

2007 ◽  
Author(s):  
Alan D. Henderson ◽  
Gregory J. Walker
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Surface Profile ◽  
Leading Edge ◽  
Suction Surface ◽  
Circular Arc ◽  
Flow Acceleration ◽  
Controlled Diffusion ◽  
Numerical Predictions ◽  
Wide Range

Laminar-turbulent transition behavior is studied near the leading edge of an outlet stator blade in a low-speed 1.5-stage axial-flow research compressor. The stator is a typical controlled diffusion design with a circular arc leading edge profile. Slow response surface pressure distribution measurements are compared with numerical predictions from the quasi two-dimensional flow solver, MISES. These both show a strong flow acceleration around each side of the circular arc, followed by a rapid deceleration near each blend point of the arc to the main surface profile. The relative magnitude of the localized overspeeds varies significantly over the wide range of stator flow incidence investigated. The unsteady boundary layer behavior on the stator is studied using a midspan array of surface-mounted hot-film sensors. On the suction surface, wake-induced transitional and turbulent strips are observed to originate close to the leading edge. The boundary layer approaches separation near the leading edge blend point on the suction surface, but this does not always lead to localized turbulent breakdown or continuous turbulent flow: a significant portion of the flow on the forward part of the surface remains laminar between the wake-induced transitional strips. At high positive incidence the wake-induced transitional strips originate near the leading edge blend point, but their growth is suppressed by the strong flow acceleration. On the pressure surface, a small separation bubble forms near the leading edge blend point resulting in almost continuous turbulent flow over the whole incidence range studied.

Observations of Transition Phenomena on a Controlled Diffusion Compressor Stator With a Circular Arc Leading Edge

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Alan D. Henderson ◽  
Gregory J. Walker
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Surface Profile ◽  
Leading Edge ◽  
Suction Surface ◽  
Circular Arc ◽  
Flow Acceleration ◽  
Controlled Diffusion ◽  
Numerical Predictions ◽  
Wide Range

Laminar-turbulent transition behavior is studied near the leading edge of an outlet stator blade in a low-speed 1.5-stage axial-flow research compressor. The stator is a typical controlled diffusion design with a circular arc leading edge profile. Slow-response surface pressure distribution measurements are compared with numerical predictions from the quasi-two-dimensional flow solver, MISES. These both show a strong flow acceleration around each side of the circular arc, followed by a rapid deceleration near each blend point of the arc to the main surface profile. The relative magnitude of the localized overspeeds varies significantly over the wide range of stator flow incidence investigated. The unsteady boundary layer behavior on the stator is studied using a midspan array of surface-mounted hot-film sensors. On the suction surface, wake-induced transitional and turbulent strips are observed to originate close to the leading edge. The boundary layer approaches separation near the leading edge blend point on the suction surface, but this does not always lead to localized turbulent breakdown or continuous turbulent flow: a significant portion of the flow on the forward part of the surface remains laminar between the wake-induced transitional strips. At high positive incidence the wake-induced transitional strips originate near the leading edge blend point, but their growth is suppressed by the strong flow acceleration. On the pressure surface, a small separation bubble forms near the leading edge blend point resulting in almost continuous turbulent flow over the whole incidence range studied.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

scholarly journals Influence of Endwall Flow on Airfoil Suction Surface Mid-Height Boundary Layer Development in a Turbine Cascade

1982 ◽  
Author(s):  
O. P. Sharma ◽  
R. A. Graziani
Keyword(s):  
Boundary Layer ◽  
Reynolds Shear Stress ◽  
Cross Flow ◽  
Prediction Method ◽  
Conservation Equation ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Extra Term ◽  
Boundary Layer Development ◽  
Layer Development

This paper presents the results of an analysis to assess the influence of cascade passage endwall flow on the airfoil suction surface mid-height boundary layer development in a turbine cascade. The effect of the endwall flow is interpreted as the generation of a cross flow and a cross flow velocity gradient in the airfoil boundary layer, which results in an extra term in the mass conservation equation. This extra term is shown to influence the boundary layer development along the mid-height of the airfoil suction surface through an increase in the boundary layer thickness and consequently an increase in the mid-height losses, and a decrease in the Reynolds shear stress, mixing length, skin friction, and Stanton number. An existing two-dimensional differential boundary layer prediction method, STAN-5, is modified to incorporate the above two effects.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Vol 126 (4) ◽  
pp. 663-676 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and reattachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Unsteady Wake-Induced Boundary Layer Transition in High Lift LP Turbines

1998 ◽  
Vol 120 (1) ◽  
pp. 28-35 ◽  
Author(s):  
V. Schulte ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Reynolds Numbers ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Lp Turbine ◽  
Wake Passing ◽  
Layer Development ◽  
Highly Loaded

The development of the unsteady suction side boundary layer of a highly loaded LP turbine blade has been investigated in a rectilinear cascade experiment. Upstream rotor wakes were simulated with a moving-bar wake generator. A variety of cases with different wake-passing frequencies, different wake strength, and different Reynolds numbers were tested. Boundary layer surveys have been obtained with a single hotwire probe. Wall shear stress has been investigated with surface-mounted hot-film gages. Losses have been measured. The suction surface boundary layer development of a modern highly loaded LP turbine blade is shown to be dominated by effects associated with unsteady wake-passing. Whereas without wakes the boundary layer features a large separation bubble at a typical cruise Reynolds number, the bubble was largely suppressed if subjected to unsteady wake-passing at a typical frequency and wake strength. Transitional patches and becalmed regions, induced by the wake, dominated the boundary layer development. The becalmed regions inhibited transition and separation and are shown to reduce the loss of the wake-affected boundary layer. An optimum wake-passing frequency exists at cruise Reynolds numbers. For a selected wake-passing frequency and wake strength, the profile loss is almost independent of Reynolds number. This demonstrates a potential to design highly loaded LP turbine profiles without suffering large losses at low Reynolds numbers.

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