scholarly journals Numerical study of surface roughness effects in the boundary layer of a blunted cone in a supersonic flow

2018 ◽  
Author(s):  
Dmitry Khotyanovsky ◽  
Alexey Kudryavtsev
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Supersonic Flow ◽  
Numerical Study ◽  
Roughness Effects

A Review of Surface Roughness Effects in Gas Turbines

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
J. P. Bons
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Gas Turbines ◽  
Engine Performance ◽  
Boundary Layer Transition ◽  
Roughness Effects ◽  
Layer Transition ◽  
Laminar Separation

The effects of surface roughness on gas turbine performance are reviewed based on publications in the open literature over the past 60 years. Empirical roughness correlations routinely employed for drag and heat transfer estimates are summarized and found wanting. No single correlation appears to capture all of the relevant physics for both engineered and service-related (e.g., wear or environmentally induced) roughness. Roughness influences engine performance by causing earlier boundary layer transition, increased boundary layer momentum loss (i.e., thickness), and/or flow separation. Roughness effects in the compressor and turbine are dependent on Reynolds number, roughness size, and to a lesser extent Mach number. At low Re, roughness can eliminate laminar separation bubbles (thus reducing loss) while at high Re (when the boundary layer is already turbulent), roughness can thicken the boundary layer to the point of separation (thus increasing loss). In the turbine, roughness has the added effect of augmenting convective heat transfer. While this is desirable in an internal turbine coolant channel, it is clearly undesirable on the external turbine surface. Recent advances in roughness modeling for computational fluid dynamics are also reviewed. The conclusion remains that considerable research is yet necessary to fully understand the role of roughness in gas turbines.

scholarly journals Surface-roughness effects on the mean flow past circular cylinders

1980 ◽  
Vol 98 (4) ◽  
pp. 673-701 ◽  
Author(s):  
O. Güven ◽  
C. Farell ◽  
V. C. Patel
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Roughness Effects ◽  
Number Range ◽  
Mean Pressure ◽  
The Mean

Measurements of mean-pressure distributions and boundary-layer development on rough-walled circular cylinders in a uniform stream are described. Five sizes of distributed sandpaper roughness have been tested over the Reynolds-number range 7 × 104to 5·5 × 105. The results are examined together with those of previous investigators, and the observed roughness effects are discussed in the light of boundary-layer theory. It is found that there is a significant influence of surface roughness on the mean-pressure distribution even at very large Reynolds numbers. This observation is supported by an extension of the Stratford–Townsend theory of turbulent boundary-layer separation to the case of circular cylinders with distributed roughness. The pressure rise to separation is shown to be closely related, as expected, to the characteristics of the boundary layer, smaller pressure rises being associated with thicker boundary layers with greater momentum deficits. Larger roughness gives rise to a thicker and more retarded boundary layer which separates earlier and with a smaller pressure recovery.

A Numerical Study of Surface Roughness Effects on Ultra-Thin Gas Films

1986 ◽  
Vol 108 (2) ◽  
pp. 171-177 ◽  
Author(s):  
J. W. White ◽  
P. E. Raad ◽  
A. H. Tabrizi ◽  
S. P. Ketkar ◽  
P. P. Prabhu
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Reynolds Equation ◽  
Numerical Study ◽  
Surface Film ◽  
Maximum Load ◽  
Roughness Effects ◽  
Number Range ◽  
Pressure Diffusion ◽  
Bearing Number

A wedge bearing with transverse sinusoidal roughness pattern is studied numerically in order to predict the effect of surface roughness on compressible fluid films. A variable grid implicit finite difference scheme is used to provide steady-state solutions of the Reynolds equation over a bearing number range of five orders of magnitude. At a fixed bearing geometry and orientation, the bearing load is found to increase to a maximum as the bearing number increases, then to decrease and asymptotically approach a limiting value as the bearing number increases further. This is quite unlike the behavior of an incompressible fluid bearing. Analysis indicates that the maximum load occurs at a condition where pressure diffusion and Couette effects of the fluid film are of an equal order of magnitude. The increased emphasis of the pressure diffusion physics is due to the short length scales of the rough surfaces which “trigger” the higher derivative diffusion terms in the Reynolds equation. The criterion required for validity of an infinite bearing number solution with a rough surface is found to be much more restrictive than that of a smooth surface bearing. Last, the type of rough surface film clearance averages used in incompressible lubrication are shown to be incorrect for analysis of very thin gas films. It would appear that one application of this information would be the design of an artificially roughened surface for the take-off and landing of magnetic head sliders so as to minimize contact and wear of the magnetic media.

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.

Roughness Effects on Frictional Resistance of Enclosed Rotating Disks

1960 ◽  
Vol 82 (3) ◽  
pp. 553-560 ◽  
Author(s):  
R. E. Nece ◽  
J. W. Daily
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Initial Point ◽  
Frictional Resistance ◽  
Reynolds Numbers ◽  
Tip Clearance ◽  
Rotating Disks ◽  
Roughness Effects ◽  
Disk Radius ◽  
Onset Of Turbulence

The effects of surface roughness on the frictional resistance of enclosed rotating disks have been studied experimentally. Torque data were obtained over the range of disk Reynolds numbers 4 × 103 to 6 × 106 for three different relative roughnesses a/k of 1000, 2000, and 3200 at three axial-clearance-to-disk-radius ratios s/a of 0.0227, 0.0609, and 0.112 for a constant, small, radial tip clearance. The existence of four possible basic flow regimes in the axial gap between the disk and casing wall was verified. Empirical expressions have been presented which predict the initial point of onset of turbulence in the flow within the boundary layer on the disk, the point at which the surface roughness becomes fully effective, and the magnitudes of the resistance coefficients in the zone of fully rough turbulent flow. The similarities and differences between smooth and rough-disk torque behavior, and to a limited extent boundary-layer behavior, have been noted.

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