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.

Influence of a Magnetic Obstacle on Forced Convection in a Three-Dimensional Duct With a Circular Cylinder

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Xidong Zhang ◽  
Hulin Huang ◽  
Yin Zhang ◽  
Hongyan Wang
Keyword(s):  
Pressure Drop ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Separated Flow ◽  
Optimum Conditions ◽  
Nusselt Numbers ◽  
Maximum Value ◽  
Wide Range ◽  
The Mean

The predictions of flow structure, vortex shedding, and drag force around a circular cylinder are promoted by both academic interest and a wide range of practical situations. To control the flow around a circular cylinder, a magnetic obstacle is set upstream of the circular cylinder in this study for active controlling the separated flow behind bluff obstacle. Moreover, the changing of position, size, and intensity of magnetic obstacle is easy. The governing parameters are the magnetic obstacle width (d/D = 0.0333, 0.1, and 0.333) selected on cylinder diameter, D, and position (L/D) ranging from 2 to 11.667 at fixed Reynolds number Rel (based on the half-height of the duct) of 300 and the relative magnetic effect given by the Hartmann number Ha of 52. Results are presented in terms of instantaneous contours of vorticity, streamlines, drag coefficient, Strouhal number, pressure drop penalty, and local and average Nusselt numbers for various magnetic obstacle widths and positions. The computed results show that there are two flow patterns, one with vortex shedding from the magnetic obstacle and one without vortex shedding. The optimum conditions for drag reduction are L/D = 2 and d/D = 0.0333–0.333, and under these conditions, the pressure drop penalty is acceptable. However, the maximum value of the mean Nusselt number of the downstream cylinder is about 93% of that for a single cylinder.

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.

scholarly journals Investigation of a Dielectric Barrier Discharge Plasma Actuator to Control Turbulent Boundary Layer Separation

2020 ◽  
Vol 10 (6) ◽  
pp. 1911 ◽  
Author(s):  
Mahdi Hasan ◽  
Michael Atkinson
Keyword(s):  
Dielectric Barrier Discharge ◽  
Barrier Discharge ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Plasma Actuator ◽  
Dbd Plasma ◽  
Dielectric Barrier ◽  
Baseline Case

A numerical investigation was carried out to explore the effects of a dielectric barrier discharge (DBD) plasma actuator on a three-dimensional incompressible, separated flow. The test article selected for the simulations was the National Aeronautical and Space Administration (NASA) wall-mounted hump model. The simulations were run at a Reynolds number of 936,000, based on hump chord length, and a freestream Mach number of 0.1. Hybrid partially averaged Navier–Stokes/large-eddy simulations (PANS/LES) were completed using CALC-LES, a well-validated computational fluid dynamics (CFD) code, developed by Chalmers University of Technology. The baseline code was modified to simulate the effects of the actuator, which were modeled as source terms in the momentum equation and were assumed to be steady and constant in the span-wise direction. The numerical simulations were carried out for a baseline (no control) case and five plasma control cases. To optimize the performance of the actuator, the variation of actuator location and voltage frequency was investigated. For the baseline case, a comparison of time-averaged skin friction, the coefficient of pressure, and velocity profiles was made of the available experimental results. The results of the baseline case showed good agreement for a hybrid turbulence model, thus strengthening the solver’s ability to predict a three-dimensional separated flow with reasonable accuracy. The results with the plasma actuator turned on showed improved flow characteristics compared to the baseline simulations by reducing the region of separated flow. The actuator placed just downstream of the separation point at an operational frequency of 5kHz completely eliminated the separated flow for our test conditions.

A Three-Dimensional Integral Method for Calculating Incompressible Turbulent Skin Friction

1975 ◽  
Vol 97 (4) ◽  
pp. 550-555 ◽  
Author(s):  
F. M. White ◽  
R. C. Lessmann ◽  
G. H. Christoph
Keyword(s):  
Skin Friction ◽  
Integral Method ◽  
Three Dimensional ◽  
Separated Flow ◽  
Turbulent Boundary Layers ◽  
Shape Factors ◽  
Coupled Partial Differential Equations ◽  
Separation Line ◽  
Curved Duct ◽  
Dimensional Integral

A new integral method is proposed for the analysis of three-dimensional incompressible turbulent boundary layers. The method utilizes velocity profile expressions in wall-law form to derive two coupled partial differential equations for the two components of surface skin friction. No shape factors or empirical shear stress correlations are needed in the method. The only requirements are a knowledge of the external velocity and streamline distribution and initial values of skin friction along a starting crossflow line of the flow. The method is insensitive to sidewall conditions and may be continued downstream until the complete three-dimensional separation line of the flow has been computed. Two comparisons with experiment are shown: a curved-duct unseparated flow and a T-shaped-box separated flow. The calculations are very straightforward and agree reasonably well with the data for friction, crossflow angle, and separation line.

scholarly journals Influence of separation structure on the dynamics of shock/turbulent-boundary-layer interactions

2021 ◽  
Author(s):  
Michael C. Adler ◽  
Datta V. Gaitonde
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Separation ◽  
High Speed ◽  
Scaling Laws ◽  
Three Dimensional ◽  
Separated Flow ◽  
Shear Layers ◽  
Underlying Structure ◽  
Mean Flow

AbstractShock/turbulent-boundary-layer interactions (STBLIs) are ubiquitous in high-speed flight and propulsion applications. Experimental and computational investigations of swept, three-dimensional (3-D) interactions, which exhibit quasi-conical mean-flow symmetry in the limit of infinite span, have demonstrated key differences in unsteadiness from their analogous, two-dimensional (2-D), spanwise-homogeneous counterparts. For swept interactions, represented by the swept–fin-on-plate and swept–compression–ramp-on-plate configurations, differences associated with the separated shear layers may be traced to the intermixing of 2-D (spanwise independent) and 3-D (spanwise dependent) scaling laws for the separated mean flow. This results in a broader spectrum of unsteadiness that includes relatively lower frequencies associated with the separated shear layers in 3-D interactions. However, lower frequency ranges associated with the global “breathing” of strongly separated 2-D interactions are significantly less prominent in these simple, swept 3-D interactions. A logical extension of 3-D interaction complexity is the compound interaction formed by the merging of two simple interactions. The first objective of this work is therefore to analyze the more complex picture of the dynamics of such interactions, by considering as an exemplar, wall-resolved simulations of the double-fin-on-plate configuration. We show that in the region of interaction merging, new flow scales, changes in separation topology, and the emergence of lower-frequency phenomena are observed, whereas the dynamics of the interaction near the fin leading edges are similar to those of the simple, swept interactions. The second objective is to evolve a unified understanding of the dynamics of STBLIs associated with complex configurations relevant to actual propulsion systems, which involve the coupling between multiple shock systems and multiple flow separation and attachment events. For this, we revisit the salient aspects of scaling phenomena in a manner that aids in assimilating the double-fin flow with simpler swept interactions. The emphasis is on the influence of the underlying structure of the separated flow on the dynamics. The distinct features of the compound interactions manifest in a centerline symmetry pattern that replaces the quasi-conical symmetry of simple interactions. The primary separation displays topological closure to reveal new length scales, associated unsteadiness bands, and secondary flow separation.

Flow separation in a rotating annulus with bottom topography

1982 ◽  
Vol 123 ◽  
pp. 303-313 ◽  
Author(s):  
M. A. Page
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Bottom Topography ◽  
Axial Rotation ◽  
Finite Depth ◽  
Boundary Layer Separation ◽  
Bottom Surface ◽  
Rotating Fluid ◽  
Interior Flow ◽  
Layer Flow

The flow in a rotating annular cylinder, of finite depth, is examined when the Rossby number Ro is O(E½), where E is the Ekman number, and when there is a topography of height O(E½) on the base of the container. The flow, relative to the rigid axial rotation, is forced by differential rotation of the lid and as it moves over the topography the streamlines are deflected parallel to the bottom surface. This induces O(1) velocity variations near the axial walls of the annulus to which the boundary layers there, of thickness O(E¼), respond. For sufficiently large values of a parameter γ ∝Ro/E½ the skin friction can vanish within these layers, with some similaritits to boundary-layer separation in a non-rotating fluid. In this study the interior flow, with horizontal viscous diffusion neglected, is calculated and used to provide a boundary condition for the, E¼ layer flow. Once λ exceeds a finite critical value a singularity is encountered in the boundary layer corresponding to flow separation from the wall. This demonstrates that E¼ layers in a rotating fluid, which for Ro = 0 have little direct influence on the interior flow, can modify the gross properties of the flow for non-zero Rossby numbers, a conclusion also reached by Walker & Stewartson (1972) in a different context.

Evaluation of the SST-SAS Model for Prediction of Separated Flow Inside Turbine Internal Cooling Passages

2016 ◽  
Author(s):  
Piotr Zacharzewski ◽  
Kathy Simmons ◽  
Richard Jefferson-Loveday ◽  
Luigi Capone
Keyword(s):  
Heat Transfer ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Separated Flow ◽  
Streamwise Velocity ◽  
Stream Velocity ◽  
Internal Cooling ◽  
Sas Model ◽  
The Hill

The flow and heat transfer over a three-dimensional axisymmetric hill and rectangular ribbed duct is computed in order to evaluate the Shear Stress Transport - Scale Adaptive Simulation (SST-SAS) turbulence model. The study presented here is relevant to turbine blade internal cooling passages and the aim is to establish whether SAS-SST is a viable alternative to other turbulence models for computations of such flows. The model investigated is based on Menter’s modification to Rotta’s k-kL model and comparison is made against experimental data as well as other models including some with scale resolving capability, such as LES, DES & hybrid LES-RANS. For the hill case the SAS model dramatically overpredicts the size of the separation bubble. The LES on the other hand proved to be more accurate even though the mesh is courser by LES standards. There is little improvement of SST-SAS compared with RANS. Broadly speaking all models predict streamwise velocity profiles for the ribbed channel with reasonable accuracy. The cross-stream velocity is underpredicted by all models. Heat transfer prediction is more accurately predicted by LES than RANS, DES & SST-SAS on a mesh that is slightly coarser than required by LES standard, however it still exhibits significant error. It is concluded that more investigation of the SST-SAS model is required to more broadly assess its viability for industrial computation.

Experiments on Supersonic Boundary-Layer Separation in Three Dimensions

1975 ◽  
Vol 42 (2) ◽  
pp. 289-294 ◽  
Author(s):  
W. D. Bachalo
Keyword(s):  
Three Dimensional ◽  
Cross Flow ◽  
Separated Flow ◽  
Flow Region ◽  
Boundary Layer Separation ◽  
Supersonic Boundary Layer ◽  
Three Dimensions ◽  
Pressure Gradients ◽  
Flat Plates ◽  
Relationship Of

A detailed experimental study of three-dimensional separation in supersonic flow is described. Three-dimensional wedges affixed to flat plates were used to generate the flow fields that were used to examine the relationship of cross flow to the extent of separation. Models with strong transverse pressure gradients resulted in a diminished extent of separation about the model plane of symmetry but demonstrated expansive growth of separation to a limit with distance from the plane of symmetry. A secondary flow region was found embedded in the separated flow.

Sign in / Sign up

Export Citation Format

Share Document