Calculation of Surface Roughness Effects on Air-Riding Seals

2004 ◽  
Vol 126 (1) ◽  
pp. 75-82 ◽  
Author(s):  
C. Guardino ◽  
J. W. Chew ◽  
N. J. Hills
Keyword(s):  
Surface Roughness ◽  
Compressible Flows ◽  
Reynolds Equation ◽  
Incompressible Flows ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Roughness Effects ◽  
Stationary Wall ◽  
Comparative Results ◽  
Effect Of Surface

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various two-dimensional or three-dimensional roughness patterns on the stationary wall. A “unit-based” approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.

Calculation of Surface Roughness Effects on Air-Riding Seals

2002 ◽  
Author(s):  
C. Guardino ◽  
J. W. Chew ◽  
N. J. Hills
Keyword(s):  
Surface Roughness ◽  
Compressible Flows ◽  
Reynolds Equation ◽  
Incompressible Flows ◽  
Numerical Solutions ◽  
Cfd Analysis ◽  
Roughness Effects ◽  
Stationary Wall ◽  
Comparative Results ◽  
Effect Of Surface

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D roughness patterns on the stationary wall. A ‘unit-based’ approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.

Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

2002 ◽  
Author(s):  
M. Eaddy ◽  
W. H. Melbourne ◽  
J. Sheridan
Keyword(s):  
Surface Roughness ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Smooth Cylinder ◽  
Lift Forces ◽  
High Reynolds ◽  
Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

On the effects of two-dimensional Reynolds roughness in hydrodynamic lubrication

1978 ◽  
Vol 364 (1716) ◽  
pp. 89-106 ◽  
Keyword(s):  
Surface Roughness ◽  
Numerical Computation ◽  
Autocorrelation Function ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
The Other ◽  
Roughness Height ◽  
Two Dimensional ◽  
Roughness Effects ◽  
Dimensional Surface

The hydrodynamic lubrication of rough surfaces is analysed with the Reynolds equation, whose application requires the roughness spacing to be large, and the roughness height to be small, compared with the thick­ness of the fluid film. The general two-dimensional surface roughness is considered, and results applicable to any roughness structure are obtained. It is revealed analytically that two types of term contribute to roughness effects: one depends on the shape of the autocorrelation function and the other does not. The former contribution was neglected by previous workers. The numerical computation of an example shows that these two contributions are comparable in magnitude.

Simulation of the subsonic flow in a high-speed centrifugal compressor impeller by the pressure-based method

1998 ◽  
Vol 212 (4) ◽  
pp. 269-287 ◽  
Author(s):  
Y Wang ◽  
S Komori
Keyword(s):  
High Speed ◽  
Compressible Flows ◽  
Incompressible Flows ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Centrifugal Impeller ◽  
Navier Stokes Equations ◽  
Compressor Impeller ◽  
Collocated Grid

A pressure-based finite volume procedure developed previously for incompressible flows is extended to predict the three-dimensional compressible flow within a centrifugal impeller. In this procedure, the general curvilinear coordinate system is used and the collocated grid arrangement is adopted. Mass-averaging is used to close the instantaneous Navier-Stokes equations. The covariant velocity components are used as the main variables for the momentum equations, making the pressure-velocity coupling easier. The procedure is successfully applied to predict various compressible flows from subsonic to supersonic. With the aid of the k-ɛ turbulence model, the flow details within a centrifugal impeller are obtained using the present procedure. Predicted distributions of the meridional velocity and the static pressure are reasonable. Calculated radial velocities and flow angles are favourably compared with the measurements at the exit of the impeller.

Measurements and Prediction of the Effects of Surface Roughness on Profile Losses and Deviation in a Turbine Cascade

1998 ◽  
Vol 120 (1) ◽  
pp. 20-27 ◽  
Author(s):  
R. J. Kind ◽  
P. J. Serjak ◽  
M. W. P. Abbott
Keyword(s):  
Surface Roughness ◽  
Three Dimensional ◽  
Leading Edge ◽  
Computational Method ◽  
Roughness Height ◽  
Surface Boundary ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Roughness Effects ◽  
Profile Losses

Measurements of pressure distributions, profile losses, and flow deviation were carried out on a planar turbine cascade in incompressible flow to assess the effects of partial roughness coverage of the blade surfaces. Spanwise-oriented bands of roughness were placed at various locations on the suction and pressure surfaces of the blades. Roughness height, spacing between roughness elements, and band width were varied. A computational method based on the inviscid/viscous interaction approach was also developed; its predictions were in good agreement with the experimental results. This indicates that good predictions can be expected for a variety of cascade and roughness configurations from any two-dimensional analysis that couples an inviscid method with a suitable rough surface boundary-layer analysis. The work also suggests that incorporation of the rough wall skin-friction law into a three-dimensional Navier–Stokes code would enable good predictions of roughness effects in three-dimensional situations. Roughness was found to have little effect on static pressure distribution around the blades and on deviation angle, provided that it does not precipitate substantial flow separation. Roughness on the suction surface can cause large increases in profile losses; roughness height and location of the leading edge of the roughness band are particularly important. Loss increments due to pressure-surface roughness are much smaller than those due to similar roughness on the suction surface.

Some Remarks on the Validity of Reynolds Equation in the Modeling of Lubricant Film Flows on the Surface Roughness Scale

2004 ◽  
Vol 126 (4) ◽  
pp. 703-710 ◽  
Author(s):  
T. Almqvist ◽  
R. Larsson
Keyword(s):  
Surface Roughness ◽  
Reynolds Equation ◽  
Numerical Solutions ◽  
Fluid Dynamic ◽  
Lubricant Film ◽  
Continuity Equations ◽  
Newtonian Case ◽  
Eyring Model ◽  
Wavelength Scale ◽  
Film Flows

The objective of this paper is to investigate the flow in a lubricant film on the surface roughness scale and to compare the numerical solutions obtained by two different solution approaches. This is accomplished firstly by the CFD-approach (computational fluid dynamic approach) where the momentum and continuity equations are solved separately, and secondly the Reynolds equation approach, which is a combination and a simplification of the above equations. The rheology is assumed to be both Newtonian and non-Newtonian. An Eyring model is used in the non-Newtonian case. The result shows that discrepancies between the two approaches may occur, primarily due to a singularity which appears in the momentum equations when the stresses in the lubricant attain magnitudes that are common in EHL. This singularity is not represented by the Reynolds equation. If, however, the rheology is shifted to a non-Newtonian Eyring model the deviations between the two solution approaches is removed or reduced. The second source of discrepancies between the two approaches is the film thickness to wavelength scale ω. It will be shown that the Reynolds equation is valid until this ratio is approximately O10−2.

Turbulent Flow Simulation of a Runner for Francis Hydraulic Turbines Using Pseudo-Compressibility

1996 ◽  
Vol 118 (2) ◽  
pp. 285-291 ◽  
Author(s):  
Chuichi Arakawa ◽  
Yi Qian ◽  
Takashi Kubota
Keyword(s):  
Compressible Flows ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Leading Edge ◽  
Design Tool ◽  
Design Flow ◽  
Navier Stokes ◽  
Small Computer ◽  
Strong Vortex

A three-dimensional Navier-Stokes code with pseudo-compressibility, an implicit formulation of finite difference, and a k – ε two-equation turbulence model has been developed for the Francis hydraulic runner. The viscous flow in the rotating field can be simulated well in the design flow operating condition as well as in the off-design conditions in which a strong vortex occurs due to the separation near the leading edge. Because the code employs an implicit algorithm and a wall function near the wall, it does not require a large CPU time. It can therefore be used on a small computer such as the desk-top workstation, and is available for use as a design tool. The same kind of algorithm that is used for compressible flows has been found to be appropriate for the simulation of complex incompressible flows in the field of turbomachinery.

Numerical Computation of Roughness Effects on Heat Transfer and Hydrodynamic Characteristics in Microchannels

2006 ◽  
Author(s):  
Heming Yun ◽  
Lin Cheng ◽  
Liqiu Wang ◽  
Binjian Chen
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Roughness Effects ◽  
Navier Stokes Equations ◽  
Experimental Heat ◽  
Macro Scale

In the present paper we focus our attention on the analysis of surface roughness effects. In the process of numerical simulation, a finite-volume method was used to solve the three-dimensional Navier-Stokes equations and energy equation. In turbulent region, wall-function was used to solve the temperature and velocity of coolant in the area near the wall. In all computational regions, the fluid-solid Conjugate heat transfer is used to solve the microchannel heat transfer problems. In conclusion the effect of surface roughness on heat transfer and pressure drop can not be neglected. And one should be very careful in ascribing the roughness effect to the discrepancies between experimental heat transfer and the prediction for standard macro scale channels.

Thermohydrodynamic Analysis of Submerged Oil Journal Bearings Considering Surface Roughness Effects

1997 ◽  
Vol 119 (1) ◽  
pp. 100-106 ◽  
Author(s):  
J. Ramesh ◽  
B. C. Majumdar ◽  
N. S. Rao
Keyword(s):  
Surface Roughness ◽  
Thermal Effects ◽  
Hydrodynamic Pressure ◽  
Height Distribution ◽  
Asperity Contact ◽  
Roughness Effects ◽  
State Behavior ◽  
Total Load ◽  
Contact Loads ◽  
Effect Of Surface

A theoretical study of a submerged oil journal bearing is made considering surface roughness and thermal effects. The total load-supporting ability under such condition is due to the thermohydrodynamic as well as the asperity contact pressure. The effect of surface roughness and viscosity-temperature dependency on hydrodynamic pressure has been found by solving the average Reynolds equation, energy equation and heat conduction equations simultaneously. The cavitation model of Jacobsson-Floberg has been modified to take the surface roughness effects into consideration. A parametric study of steady-state behavior has been carried out. Finally, the isothermal, thermohydrodynamic, and contact loads for a model bearing have been calculated, assuming the surface height distribution as Gaussian.

Surface Roughness Effects in High-Speed Hydrodynamic Journal Bearings

1997 ◽  
Vol 119 (4) ◽  
pp. 776-780 ◽  
Author(s):  
H. Hashimoto
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Reynolds Equation ◽  
Computation Time ◽  
Experimental Results ◽  
Roughness Effects ◽  
Modified Reynolds Equation ◽  
Nonlinear Simultaneous Equations ◽  
Theoretical Results ◽  
Good Agreement

This paper describes an applicability of modified Reynolds equation considering the combined effects of turbulence and surface roughness, which was derived by Hashimoto and Wada (1989), to high-speed journal bearing analysis by comparing the theoretical results with experimental ones. In the numerical analysis of modified Reynolds equation, the nonlinear simultaneous equations for the turbulent correction coefficients are greatly simplified to save computation time with a satisfactory accuracy under the assumption that the shear flow is superior to the pressure flow in the lubricant films. The numerical results of Sommerfeld number and attitude angle are compared with the experimental results to confirm the applicability of the modified Reynolds equation in the case of two types of bearings with different relative roughness heights. Good agreement was obtained between theoretical and experimental results.

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