scholarly journals Viscous Effects in the Inception of Cavitation on Axisymmetric Bodies

1973 ◽  
Vol 95 (4) ◽  
pp. 519-527 ◽  
Author(s):  
V. H. Arakeri ◽  
A. J. Acosta
Keyword(s):  
Boundary Layer ◽  
Experimental Evidence ◽  
Flow Separation ◽  
Pressure Coefficient ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Visualization Method ◽  
Viscous Effects ◽  
Cavitation Inception ◽  
Axisymmetric Bodies

Cavitation inception and development on two axisymmetric bodies was studied with the aid of a Schlieren flow visualization method developed for that purpose. Both bodies were found to exhibit a laminar boundary layer separation; cavitation inception was observed to occur within this region of separated flow. The incipient cavitation index was found to be closely correlated with the magnitude of the pressure coefficient at the location of flow separation on one of the bodies. There is also experimental evidence that events at the site of turbulent reattachment of the separated flow may also greatly influence cavitation inception.

Comparison of Inviscid Computations With Theory and Experiment in Vibrating Transonic Compressor Cascades

1990 ◽  
Author(s):  
G. A. Gerolymos ◽  
E. Blin ◽  
H. Quiniou
Keyword(s):  
Boundary Layer ◽  
Plate Theory ◽  
Strong Shock ◽  
Acoustic Resonance ◽  
Boundary Layer Separation ◽  
Computational Method ◽  
Viscous Effects ◽  
Transonic Compressor ◽  
Boundary Layer Interaction ◽  
Interaction Regions

The prediction of unsteady flow in vibrating transonic cascades is essential in assessing the aeroelastic stability of fans and compressors. In the present work an existing computational code, based on the numerical integration of the unsteady Euler equations, in blade-to-blade surface formulation, is validated by comparison with available theoretical and experimental results. Comparison with the flat plate theory of Verdon is, globally, satisfactory. Nevertheless, the computational results do not exhibit any particular behaviour at acoustic resonance. The use of a 1-D nonreflecting boundary condition does not significantly alter the results. Comparison of the computational method with experimental data from started and unstarted supersonic flows, with strong shock waves, reveals that, notwithstanding the globally satisfactory performance of the method, viscous effects are prominent at the shock wave/boundary layer interaction regions, where boundary layer separation introduces a pressure harmonic phase shift, which is not presicted by inviscid methods.

A Model for High-Reynolds-Number Flow Past Rough-Walled Circular Cylinders

1977 ◽  
Vol 99 (3) ◽  
pp. 486-493 ◽  
Author(s):  
O. Gu¨ven ◽  
V. C. Patel ◽  
C. Farell
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Pressure Coefficient ◽  
Empirical Relation ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow

A simple analytical model for two-dimensional mean flow at very large Reynolds numbers around a circular cylinder with distributed roughness is presented and the results of the theory are compared with experiment. The theory uses the wake-source potential-flow model of Parkinson and Jandali together with an extension to the case of rough-walled circular cylinders of the Stratford-Townsend theory for turbulent boundary-layer separation. In addition, a semi-empirical relation between the base-pressure coefficient and the location of separation is used. Calculation of the boundary-layer development, needed as part of the theory, is accomplished using an integral method, taking into account the influence of surface roughness on the laminar boundary layer and transition as well as on the turbulent boundary layer. Good agreement with experiment is shown by the results of the theory. The significant effects of surface roughness on the mean-pressure distribution on a circular cylinder at large Reynolds numbers and the physical mechanisms giving rise to these effects are demonstrated by the model.

Boundary Layer Separation Control With Fluidic Oscillators

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ciro Cerretelli ◽  
Kevin Kirtley
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Maximum Pressure ◽  
Suction Surface ◽  
Stator Vane ◽  
Average Operating ◽  
Fluidic Actuators ◽  
Layer Flow

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to “repair” the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and is therefore more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% rms of the average operating at nondimensional blowing frequencies (F+) in the range of 0.6<F+<6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared with optimal steady blowing. Particle image velocimetry velocity and vorticity measurements have been performed, which show no large-scale unsteadiness in the controlled boundary layer flow.

Hypersonic Flow Separation in Shock Wave Boundary Layer Interactions

1992 ◽  
Author(s):  
A. Hamed ◽  
Ajay Kumar
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Separation ◽  
Characteristic Length ◽  
Separated Flow ◽  
Surface Cooling ◽  
Flat Plates ◽  
Shock Interactions ◽  
Wave Boundary ◽  
Incipient Separation

This work presents an assessment of the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consist of selected configurations where the only characteristic length in the interation is the incoming boundary layer thickness. It consists of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the empirical correlations for incipient separation are reviewed. The effects of Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed.

Flow Separation in Shock Wave Boundary Layer Interactions

1994 ◽  
Vol 116 (1) ◽  
pp. 98-103 ◽  
Author(s):  
A. Hamed ◽  
A. Kumar
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Separation ◽  
Characteristic Length ◽  
Separated Flow ◽  
Surface Cooling ◽  
Flat Plates ◽  
Shock Interactions ◽  
Wave Boundary ◽  
Incipient Separation

This work presents an assessment of the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists of selected configurations where the only characteristic length in the iteration is the incoming boundary layer thickness. It consists of two-dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the empirical correlations for incipient separation are reviewed. The effects of Mach number, Reynolds number, surface cooling, and the methods of detecting separation are discussed.

Boundary-layer separation of rotating flows past surface-mounted obstacles

1992 ◽  
Vol 237 ◽  
pp. 343-371 ◽  
Author(s):  
K. J. Richards ◽  
D. A. Smeed ◽  
E. J. Hopfinger ◽  
G. Chabert D'Hières
Keyword(s):  
Flow Separation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Critical Value ◽  
Complex Stress ◽  
Rotating Fluid ◽  
Separation Line ◽  
Maximum Value ◽  
The Hill

This paper describes laboratory experiments on the flow over a three-dimensional hill in a rotating fluid. The experiments were carried out in towing tanks, placed on rotating tables. Rotation is found to have a strong influence on the separation behind the hill. The topology of the separation is found to be the same for all the flows examined. The Rossby number R in the experiments is of order 1, the maximum value being 6. The separated flow is dominated by a single trailing vortex. In the majority of cases the surface stress field has a single separation line and there are no singular points. In a few experiments at the highest Rossby numbers the observations suggest more complex stress fields but the results are inconclusive.A criterion for flow separation is sought. For values of D/L > 1, where D is the depth of the flow and L the lengthscale of the hill, separation is found to be primarily dependent on R. At sufficiently small values of R separation is suppressed and the flow remains fully attached.Linear theory is found to give a good estimate for the critical value of R for flow separation. For hills with a moderate slope (slope ≤ 1) this critical value is around 1, decreasing with increasing slope. It is postulated that the existence of a single dominant trailing vortex is due to the uplifting and subsequent turning of transverse vorticity generated by surface pressure forces upstream of the separation line.

Experimental Investigation of Free Stream Turbulence Effects on Flow Separation

2003 ◽  
Author(s):  
Mahmoud Ardebili ◽  
Yiannis Andreopoulos
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Flow Separation ◽  
Large Scale ◽  
Free Stream ◽  
Pressure Coefficient ◽  
Free Stream Turbulence ◽  
Vorticity Flux

An experimental investigation of a separated boundary layer flow has been attempted which has been created by perturbing a flat plate flow with a favorable pressure gradient immediately followed by an adverse pressure gradient. The aim of the research program is possible control of flow separation by means of free stream turbulence. The flow is configured in a large-scale low speed wind tunnel where measurements of turbulence can be obtained with high spatial and temporal resolution. A model has been designed by using CFD analysis. Mean wall pressure and vorticity flux measurements are reported in this paper. Twelve experiments with three different mesh size grids at three different Reynolds numbers have been carried out. Three bulk flow parameters seem to characterize the flow: The Reynolds number of the boundary layer, Re+, the Reynolds number of the flow through the grid, ReM, and the solidity of the grid. It was found that the pressure coefficient depends weakly on the solidity of the grids. Vorticity flux also depends on the grid used to generate free stream turbulence. The location of maximum or minimum vorticity flux moves upstream at higher ReM.

Boundary Layer Separation Control With Fluidic Oscillators

2006 ◽  
Author(s):  
Ciro Cerretelli ◽  
Kevin Kirtley
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Maximum Pressure ◽  
Suction Surface ◽  
Stator Vane ◽  
Average Operating ◽  
Fluidic Actuators ◽  
Layer Flow

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to repair the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and therefore is more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% RMS of the average operating at non-dimensional blowing frequencies (F+) in the range 0.6 < F+ < 6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared to optimal steady blowing. PIV velocity and vorticity measurements have been performed that show no large-scale unsteadiness in the controlled boundary layer flow.

Cavitation Inception Observations on Axisymmetric Bodies at Supercritical Reynolds Numbers

1976 ◽  
Vol 20 (01) ◽  
pp. 40-50
Author(s):  
V. H. Arakeri ◽  
A. J. Acosta
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
The Body ◽  
Laminar Separation ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Pressure Point ◽  
A Site ◽  
Axisymmetric Bodies

A laminar separation on a body provides a site for the inception of cavitation. The separated region disappears when the boundary layer upstream becomes turbulent; this may occur naturally or by stimulation. The consequences of this disappearance on the values of the cavitation inception index and the type and appearance of the cavitation at inception are investigated on three different axisymmetric bodies. On one of these bodies, a hemisphere-cylinder, a trip near the nose so energized the boundary layer that it was impossible for any form of cavitation to remain attached to the body even when a tension of about one half atm. existed at the minimum pressure point on the body.

Analysis of Laminar Boundary-Layer Separation in Retarded Flow over Bodies of Revolution

2021 ◽  
Author(s):  
Ahmer Mehmood ◽  
Babar Hussain Shah ◽  
Muhammad Usman ◽  
Iqrar Raza
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Separation ◽  
Boundary Layer Separation ◽  
The Body ◽  
Bodies Of Revolution ◽  
Layer Separation ◽  
Transverse Curvature ◽  
Favorable Pressure Gradient ◽  
Curvature Parameter

Laminar boundary-layer separation phenomenon is one of the interesting and important aspects of boundary-layer flows. It occurs in various physical situations because of decreasing wall shear stress. Retarded flow velocities are one of the reasons to happen this event. Flow separation can be prevented or delayed by utilizing bodies of revolution as surface transverse curvature produces the effects of the nature of favorable pressure-gradient which in turn increases wall shear stress that keeps the flow attached to the surface. Bodies of revolution whose body contour follows power-law form also play a vital role to delay flow separation. Bodies of revolution of varying cross-sections and involving surface transverse curvature (TVC) are utilized to examine their effects on flow separation. Particularly, a convex transverse curvature has been considered due to its effects of the nature of favorable pressure-gradient which causes to delay the flow separation. A retarded flow velocity of Görtler’s type is considered in this study to investigate flow separation process. A detailed analysis is provided to understand the flow separation by calculating separation points under various assumptions. It has been observed that the body contours exponent n and the convex transverse curvature parameter k play an assistive role in the delaying of boundary-layer separation even under the influence of strong retardation. Results are presented through various Tables and graphs in order to highlight the role of the power-law exponent of external velocity m, the convex transverse curvature parameter k, and the body contours exponent n on separation points.

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