Numerical Study of Transitional Rough Wall Boundary Layer

2012 ◽  
Author(s):  
Witold Elsner ◽  
Piotr Warzecha
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Flat Plate ◽  
Turbine Blade ◽  
Numerical Study ◽  
Suction Side ◽  
Rough Wall ◽  
Correct Prediction ◽  
Modeling Approach ◽  
Highly Loaded

The paper presents the verification of boundary layer modeling approach, which relies on a γ-Reθt model proposed by Menter et al. [1]. This model was extended by laminar-turbulent transition correlations proposed by Piotrowski et al. [2] as well as Stripf et al. [3] correlations, which take into account the effects of surface roughness. To blend between the laminar and fully turbulent boundary layer over rough wall the modified intermittency equation is used. To verify the model a flat plate with zero and non-zero pressure gradients test cases as well as the high pressure turbine blade case were chosen. Further on, the model was applied for unsteady calculations of turbine blade profile as well as the Lou and Hourmouziadis [4] flat plate test case, with induced pressure profile typical for suction side of highly-loaded turbine airfoil. The combined effect of roughness and wake passing were studied. The studies proved that the proposed modeling approach (ITMR hereinafter) appeared to be sufficiently precise and enabled for a qualitatively correct prediction of the boundary layer development for the tested simple flow configurations. The results of unsteady calculations indicated that the combined impact of wakes and the surface roughness could be beneficial for the efficiency of the blade rows, but mainly in the case of strong separation occurring on highly-loaded blade profiles. It was also demonstrated that the roughness hardly influences the location of wake induced transition, but has an impact on the flow in between the wakes.

Numerical Study of Transitional Rough Wall Boundary Layer

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Witold Elsner ◽  
Piotr Warzecha
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Flat Plate ◽  
Turbine Blade ◽  
Numerical Study ◽  
Rough Wall ◽  
Blade Profile ◽  
Modeling Approach ◽  
Wall Boundary ◽  
Highly Loaded

This paper presents the verification of the boundary layer modeling approach, which relies on a γ-Reθt model proposed by Menter et al. (2006, “A Correlation-Based Transition Model using Local Variables—Part I: Model Formation,” J. Turbomach., 128(3), pp. 413–422). This model was extended by laminar-turbulent transition correlations proposed by Piotrowski et al. (2008, “Transition Prediction on Turbine Blade Profile with Intermittency Transport Equation,” Proceedings of the ASME Turbo Expo, Paper No. GT2008-50796) as well as Stripf et al.'s (2009, “Extended Models for Transitional Rough Wall Boundary Layers with Heat Transfer—Part I: Model Formulation,” J. Turbomach., 131(3), 031016) correlations, which take into account the effects of surface roughness. To blend between the laminar and fully turbulent boundary layer over rough wall, the modified intermittency equation is used. To verify the model, a flat plate with zero and nonzero pressure gradient test cases as well as the high pressure turbine blade case were chosen. Furthermore, the model was applied for unsteady calculations of the turbine blade profile as well as the Lou and Hourmouziadis (2000, “Separation Bubbles Under Steady and Periodic-Unsteady Main Flow Conditions,” J. Turbomach., 122(4), pp. 634–643) flat plate test case, with an induced pressure profile typical for a suction side of highly-loaded turbine airfoil. The combined effect of roughness and wake passing were studied. The studies proved that the proposed modeling approach (ITMR hereinafter) appeared to be sufficiently precise and enabled for a qualitatively correct prediction of the boundary layer development for the tested simple flow configurations. The results of unsteady calculations indicated that the combined impact of wakes and the surface roughness could be beneficial for the efficiency of the blade rows, but mainly in the case of strong separation occurring on highly-loaded blade profiles. It was also demonstrated that the roughness hardly influences the location of wake induced transition, but has an impact on the flow in between the wakes.

A Comparative Numerical Study of Aerodynamics and Heat Transfer on Transitional Flow Around a Highly Loaded Turbine Blade With Flow Separation Using RANS, URANS and LES

2014 ◽  
Author(s):  
Meinhard T. Schobeiri ◽  
Ali Nikparto
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbine Blade ◽  
Numerical Study ◽  
Transitional Flow ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Eddy Simulation ◽  
Reynolds Averaged Navier Stokes ◽  
Highly Loaded

The paper numerically and experimentally investigates the behavior of the boundary layer development and heat transfer along the suction and pressure surfaces of a highly loaded turbine blade with separation. To evaluate and compare the predictive capability of different numerical methods, Reynolds Averaged Navier-Stokes based solvers (RANS), Unsteady Reynolds Averaged Navier Stokes equation (URANS) as well as Large Eddy Simulation (LES) are used. The results of each individual numerical method are compared with the measurements. For this purpose, extensive boundary layer and heat transfer measurements were performed in the unsteady boundary layer cascade facility of the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. Aerodynamics experiments include measuring the onset of the boundary, its transition, separation and re-attachment using miniature hot wire probes. Heat transfer measurements along the suction and pressure surfaces were conducted utilizing a specially designed heat transfer blade that was instrumented with liquid crystal coating. Comparisons of the experimental and numerical results detail differences in predictive capabilities of the RANS based solvers and LES.

Aerodynamic Effects of Non-Uniform Surface Roughness on a Turbine Blade

2013 ◽  
Author(s):  
Sebastian Hohenstein ◽  
Jens Aschenbruck ◽  
Joerg Seume
Keyword(s):  
Surface Roughness ◽  
Turbine Blade ◽  
Thermal Loading ◽  
Numerical Study ◽  
Suction Side ◽  
Automatic Design ◽  
High Pressure Turbine ◽  
Fully Automatic ◽  
The Given ◽  
Cord Length

The effect on non-uniform surface roughness on the aerodynamics of a turbine blade is investigated. Surface roughness on airfoils has a significant impact on total energy loss due to skin friction and typically leads to an increased thermal loading. In the present research project, investigations are supposed to be carried out experimentally. For this a blade must be designed, which accommodates the contradictory requirements of aerodynamics and manufacturing the sections of surface roughness. A fully automatic design process based on a genetic algorithm is developed and results are shown. The designed blade sufficiently fulfills the given requirements. A numerical study, using a low-Reynolds approach, is performed to investigate the influence of non-uniform roughness applied to different positions on the suction side of a high pressure turbine blade. It is shown that roughness applied at the leading and trailing edge does not significantly influence the flow whereas roughness at 20% cord length and at midchord induce transition. Especially surface roughness at 20% chord length shows a strong correlation to the change of total pressure loss.

The Influence of Technical Surface Roughness on the Flow Around a Highly Loaded Compressor Cascade

1999 ◽  
Author(s):  
Robert Leipold ◽  
Matthias Boese ◽  
Leonhard Fottner
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Pressure Distribution ◽  
Total Pressure ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Highly Loaded

A highly loaded compressor cascade which features a chord length that is ten times larger than in real turbomachinary is used to perform an investigation of the influence of technical surface roughness. The surface structure of a precision forged blade was engraved in two 0.3mm thick sheets of copper with the above mentioned enlarging factor (Leipold and Fottner, 1998). To avoid additional effects due to thickening of the blade contour the sheets of copper are applied as inlay’s to the pressure and suction side. At the high speed cascade wind tunnel the profile pressure distribution and the total pressure distribution at the exit measurement plane were measured for the rough and the smooth blade for a variation of inlet flow angle and inlet Reynolds number. For some interesting flow conditions the boundary layer development was investigated with the laser-two-focus anemometry and the one-dimensional hot-wire anemometry. At low Reynolds numbers and small inlet angles a separation bubble is only slightly reduced due to surface roughness. The positive effect of a reduced separation bubble is overcompensated by a negative influence of surface roughness on the turbulent boundary layer downstream of the separation bubble. At high Reynolds numbers the flow over the rough blade shows a turbulent separation leading to high total pressure loss coefficients. The laser-two-focus measurements indicate a velocity deficit close to the trailing edge even at flow conditions where positive effects due to a reduction of the suction side separation have been expected. The turbulence intensity is reduced close downstream of the separation bubble but increased further downstream due to surface roughness. Thus not the front part but the rear part of the blade reacts sensitively on surface roughness.

The Influence of Technical Surface Roughness Caused by Precision Forging on the Flow Around a Highly Loaded Compressor Cascade

1999 ◽  
Vol 122 (3) ◽  
pp. 416-424 ◽  
Author(s):  
Robert Leipold ◽  
Matthias Boese ◽  
Leonhard Fottner
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Pressure Distribution ◽  
Total Pressure ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Highly Loaded

A highly loaded compressor cascade, which features a chord length ten times larger than in real turbomachinery, is used to perform an investigation of the influence of technical surface roughness. The surface structure of a precision forged blade was engraved in two 0.3-mm-thick sheets of copper with the above-mentioned enlarging factor (Leipold and Fottner, 1996). To avoid additional effects due to thickening of the blade contour, the sheets of copper are applied as inlays to the pressure and suction side. At the high-speed cascade wind tunnel, the profile pressure distribution and the total pressure distribution at the exit measurement plane were measured for the rough and the smooth blade for a variation of inlet flow angle and inlet Reynolds number. For some interesting flow conditions, the boundary layer development was investigated with laser-two-focus anemometry and one-dimensional hot-wire anemometry. At low Reynolds numbers and small inlet angles, a separation bubble is only slightly reduced due to surface roughness. The positive effect of a reduced separation bubble is overcompensated by a negative influence of surface roughness on the turbulent boundary layer downstream of the separation bubble. At high Reynolds numbers, the flow over the rough blade shows a turbulent separation leading to high total pressure loss coefficients. The laser-two-focus measurements indicate a velocity deficit close to the trailing edge, even at flow conditions where positive effects due to a reduction of the suction side separation have been expected. The turbulence intensity is reduced close downstream of the separation bubble but increased further downstream due to surface roughness. Thus the rear part of the blade but not the front part reacts sensitively on surface roughness. [S0889-504X(00)01302-7]

The Effect of Surface Roughness and Favorable Pressure Gradient on Turbulent Boundary Layers

2011 ◽  
Author(s):  
Ju Hyun Shin ◽  
Seung Jin Song
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Flat Plate ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Layer Growth ◽  
Rough Wall ◽  
Favorable Pressure Gradient

Rough wall turbulent boundary layers subjected to pressure gradient have engineering interest for many fluid machinery applications. A number of investigations have been made to understand surface roughness and pressure gradient effects on turbulent boundary layer characteristics, but separately. In this paper, turbulent boundary layers over a flat plate with surface roughness and favorable pressure gradient (FPG) are experimentally investigated. Boundary layers in different streamwise locations were measured using boundary layer type hot-wire anemometry. Rough wall zero pressure gradient (ZPG) turbulent boundary layers were also measured to compare the result from the investigation. The surface roughness was applied by attaching sandpapers on the flat plate. The magnitude of surface roughness is representative of land-based gas turbine compressor blade. Pressure gradient was adjusted using movable endwall of the test section. Results from the measurement show characteristics of the turbulent boundary layer growth affected by both surface roughness and favorable pressure gradient.

Numerical Study of Boundary Layers With Reverse Wedge Flows Over a Semi-Infinite Flat Plate

2009 ◽  
Vol 77 (2) ◽  
Author(s):  
R. Ahmad ◽  
K. Naeem ◽  
Waqar Ahmed Khan
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Numerical Study ◽  
Boundary Layer Equation ◽  
Wedge Angle ◽  
Adverse Pressure Gradient ◽  
Problem Solution ◽  
Weighted Residual Method ◽  
Boundary Layer Problem ◽  
Layer Problem

This paper presents the classical approximation scheme to investigate the velocity profile associated with the Falkner–Skan boundary-layer problem. Solution of the boundary-layer equation is obtained for a model problem in which the flow field contains a substantial region of strongly reversed flow. The problem investigates the flow of a viscous liquid past a semi-infinite flat plate against an adverse pressure gradient. Optimized results for the dimensionless velocity profiles of reverse wedge flow are presented graphically for different values of wedge angle parameter β taken from 0≤β≤2.5. Weighted residual method (WRM) is used for determining the solution of nonlinear boundary-layer problem. Finally, for β=0 the results of WRM are compared with the results of homotopy perturbation method.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

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