scholarly journals On-wall and interior separation in a two-fluid boundary layer

2019 ◽  
Vol 119 (1) ◽  
pp. 1-21
Author(s):  
Sergei N. Timoshin ◽  
Pallu Thapa
Keyword(s):  
Boundary Layer ◽  
Pressure Variation ◽  
Flow Reversal ◽  
Reversed Flow ◽  
Two Fluids ◽  
Transverse Pressure ◽  
Fluid Boundary ◽  
Interior Flow ◽  
High Reynolds ◽  
Two Fluid

Abstract A two-fluid boundary layer is considered in the context of a high Reynolds number Poiseuille–Couette channel flow encountering an elongated shallow obstacle. The flow is laminar, steady and two-dimensional, with the boundary layer shown to have the pressure unknown in advance and a specified displacement (a condensed boundary layer). The focus is on the detail of the flow reversal triggered by the obstacle. The interface between the two fluids passes through the boundary layer which, in conjunction with the effects of gravity and distinct densities in the two fluids, leads to several possible topologies of the reversed flow, including a conventional on-wall separation, interior flow reversal above the interface, and several combinations of the two. The effect of upstream influence due to a transverse pressure variation under gravity is mentioned briefly.

Mode coalescence in a two-fluid boundary-layer stability problem

2000 ◽  
Vol 12 (8) ◽  
pp. 1969-1978 ◽  
Author(s):  
S. N. Timoshin ◽  
A. P. Hooper
Keyword(s):  
Boundary Layer ◽  
Stability Problem ◽  
Boundary Layer Stability ◽  
Fluid Boundary ◽  
Two Fluid

On shear sheltering and the structure of vortical modes in single- and two-fluid boundary layers

2009 ◽  
Vol 626 ◽  
pp. 111-147 ◽  
Author(s):  
TAMER A. ZAKI ◽  
SANDEEP SAHA
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Layer Structure ◽  
Inviscid Limit ◽  
Linear Perturbation ◽  
Perturbation Equation ◽  
Diffusive Regime ◽  
Fluid Boundary ◽  
Two Fluid

Studies of vortical interactions in boundary layers have often invoked the continuous spectrum of the Orr–Sommerfeld (O-S) equation. These vortical eigenmodes provide a link between free-stream disturbances and the boundary-layer shear – a link which is absent in the inviscid limit due to shear sheltering. In the presence of viscosity, however, a shift in the dominant balance in the operator determines the structure of these eigenfunctions inside the mean shear. In order to explain the mechanics of shear sheltering and the structure of the continuous modes, both numerical and asymptotic solutions of the linear perturbation equation are presented in single- and two-fluid boundary layers. The asymptotic analysis identifies three limits: a convective shear-sheltering regime, a convective–diffusive regime and a diffusive regime. In the shear-dominated limit, the vorticity eigenfunction possesses a three-layer structure, the topmost being a region of exponential decay. The role of viscosity is most pronounced in the diffusive regime, where the boundary layer becomes ‘transparent’ to the oscillatory eigenfunctions. Finally, the convective–diffusive regime demonstrates the interplay between the the accumulative effect of the shear and the role of viscosity. The analyses are complemented by a physical interpretation of shear-sheltering mechanism. The influence of a wallfilm, in particular viscosity and density stratification, and surface tension are also evaluated. It is shown that a modified wavenumber emerges across the interface and influences the penetration of vortical disturbances into the two-fluid shear flow.

Two-fluid boundary layer stability

1998 ◽  
Vol 10 (11) ◽  
pp. 2746-2757 ◽  
Author(s):  
S. Özgen ◽  
G. Degrez ◽  
G. S. R. Sarma
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Stability ◽  
Fluid Boundary ◽  
Two Fluid

Two Fluid Modeling of Microbubble Turbulent Drag Reduction

2003 ◽  
Author(s):  
Robert F. Kunz ◽  
Steven Deutsch ◽  
Jules W. Lindau
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Flat Plate ◽  
Skin Friction ◽  
High Reynolds Number ◽  
Fluid Modeling ◽  
Wall Shear ◽  
High Reynolds ◽  
Two Fluid

An unstructured 3D multiphase CFD method has been adapted and applied for the modeling of high Reynolds number external flows with microbubble drag reduction (MDR). An ensemble averaged multi-field two-fluid baseline differential model is employed. Interfacial dynamics models are incorporated to account for drag, lift, virtual mass and dispersion. Wall kinematic constraints, porous-wall shear apportionment, coalescence, breakup and attendant turbulence attenuation are also accounted for. The results of several high Reynolds number applications are presented, including quasi-1D analysis of an equilibrium bubbly boundary layer, 2D analysis of flat plate flow across a range of gas injection flow rates, and 3D analysis of a notional high lift hydrofoil with MDR. For the flat plate analyses, quantitative comparisons are made with available experimental skin friction measurements, and qualitative comparisons are made with available volume fraction profile measurements. Though some accuracy shortcomings remain, the generally good agreement observed serves to validate the appropriateness of two-fluid modeling in these flows, while elucidating areas where modeling improvements can be made. It is observed that the extraction of turbulent kinetic energy from the liquid phase by the action of bubble breakup can be a significant source of skin friction reduction. Also, the role of mixture density in the boundary layer on wall shear stress is discussed in the context of the homogenous mixture and two-fluid simulations presented.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

Flow Reversal in Opposing Mixed Convection Flow in Inclined Pipes

1989 ◽  
Vol 111 (1) ◽  
pp. 114-120 ◽  
Author(s):  
A. S. Lavine ◽  
M. Y. Kim ◽  
C. N. Shores
Keyword(s):  
Mixed Convection ◽  
Tilt Angle ◽  
Maximum Flow ◽  
Flow Reversal ◽  
Transition To Turbulence ◽  
Convection Flow ◽  
Periodic Behavior ◽  
Tube Cross Section ◽  
High Reynolds ◽  
Inclined Pipe

An experimental investigation of opposing mixed convection in an inclined pipe has been conducted. Dye injection reveals the existence of flow reversal regions. There is an optimal tilt angle that yields maximum flow reversal length. Flow reversals are seen to cause early transition to turbulence. Temperature profiles are measured across the tube cross section near the entrance to the heated section, and show the effect of tube inclination. Temperature measurements exhibit periodic behavior in the flow reversal region under some conditions, generally characterized by low tilt angle and moderate to high Reynolds and Grashof numbers. Flow visualization indicates that this periodic behavior is due to the intermittent breakdown of the flow reversal region.

Free-stream coherent structures in parallel boundary-layer flows

2014 ◽  
Vol 752 ◽  
pp. 602-625 ◽  
Author(s):  
Kengo Deguchi ◽  
Philip Hall
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Coherent Structures ◽  
Free Stream ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Homotopy Continuation ◽  
Boundary Layer Flows ◽  
Navier Stokes Equations ◽  
High Reynolds

AbstractOur concern in this paper is with high-Reynolds-number nonlinear equilibrium solutions of the Navier–Stokes equations for boundary-layer flows. Here we consider the asymptotic suction boundary layer (ASBL) which we take as a prototype parallel boundary layer. Solutions of the equations of motion are obtained using a homotopy continuation from two known types of solutions for plane Couette flow. At high Reynolds numbers, it is shown that the first type of solution takes the form of a vortex–wave interaction (VWI) state, see Hall & Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666), and is located in the main part of the boundary layer. On the other hand, here the second type is found to support an equilibrium solution of the unit-Reynolds-number Navier–Stokes equations in a layer located a distance of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}O(\ln \mathit{Re})$ from the wall. Here $\mathit{Re}$ is the Reynolds number based on the free-stream speed and the unperturbed boundary-layer thickness. The streaky field produced by the interaction grows exponentially below the layer and takes its maximum size within the unperturbed boundary layer. The results suggest the possibility of two distinct types of streaky coherent structures existing, possibly simultaneously, in disturbed boundary layers.

Characterization of the Custom-Designed, High Reynolds Number Water Tunnel

2016 ◽  
Author(s):  
Yasaman Farsiani ◽  
Brian R. Elbing
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Test Section ◽  
High Reynolds Number ◽  
Layer Growth ◽  
Water Tunnel ◽  
Freestream Velocity ◽  
Section Design ◽  
High Reynolds

This paper reports on the characterization of the custom-designed high-Reynolds number recirculating water tunnel located at Oklahoma State University. The characterization includes the verification of the test section design, pump calibration and the velocity distribution within the test section. This includes an assessment of the boundary layer growth within the test section. The tunnel was designed to achieve a downstream distance based Reynolds number of 10 million, provide optical access for flow visualization and minimize inlet flow non-uniformity. The test section is 1 m long with 15.2 cm (6-inch) square cross section and acrylic walls to allow direct line of sight at the tunnel walls. The verification of the test section design was accomplished by comparing the flow quality at different location downstream of the flow inlet. The pump was calibrated with the freestream velocity with three pump frequencies and velocity profiles were measured at defined locations for three pump speeds. Boundary layer thicknesses were measured from velocity profile results and compared with analytical calculations. These measurements were also compared against the facility design calculations.

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