scholarly journals Influence of upstream flow characteristics on the reattachment phenomenon in shallow cavities

2011 ◽  
Vol 15 (3) ◽  
pp. 721-734 ◽  
Author(s):  
Arous Madi ◽  
Amina Mataoui ◽  
Zahia Bouahmed
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Boundary Layer Flow ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Numerical Approach ◽  
Wall Jet ◽  
Shallow Cavity ◽  
Layer Flow ◽  
Upstream Flow

The influence of the upstream flow characteristics on the behavior of the flow over a shallow cavity and on the reattachment phenomenon is examined in this paper. Accordingly, a comparison of the cavity?s flow structure is performed for two different upstream flows: the wall jet flow and the boundary layer flow. The wall jet possesses a particular structure with two regions: an inner layer analogous to that of a boundary layer and an outer layer similar to that of a free jet; this layer is an additional source of turbulence production in addition to that of the inner shear layer. The present study interested to the effect of this external layer on the shallow cavity?s flow. The numerical approach is based on the low Reynolds stress-omega turbulence model. Fluent 6.3 and the pre-processor Gambit 2.3 are used for the computation. The numerical results indicate that the flow structure is very sensitive to the upstream flow?s characteristics. Indeed, for the same Reynolds number and the same boundary layer thickness at the cavity leading edge, the cavity flow structure in a wall jet upstream flow case differs considerably from that of a boundary layer upstream flow. The most important finding is the earlier reattachment process in the wall jet inflow case, where an important reduction of the reattachment length is observed compared to that of a cavity under a boundary layer flow.

Criteria for Boundary Layer Transition

2011 ◽  
Author(s):  
Stefan Becker ◽  
Donald M. McEligot ◽  
Edmond Walsh ◽  
Eckart Laurien
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Layer Flow

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.

Flow Characteristics around Circular Cylinders with a Normal Slit

2017 ◽  
Vol 379 ◽  
pp. 48-57 ◽  
Author(s):  
Cheng Hsiung Kuo ◽  
Hwa Wei Lin ◽  
Chih Tao Chai ◽  
Fred Cheng
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Flow ◽  
Rear Surface ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Phase Lock ◽  
Layer Flow

Alterations of boundary layer separation along the upper-rear surface of a baseline and slit cylinder and the formation of a vortex in the near-wake are investigated by particle image velocimetry (PIV) at Reynolds number 1000. The slit ratio (S/D) is 0.3. The phase-lock flow structures are referred to the time-dependent volume flux at the slit exit and are achieved by the modified phase-averaged technique. The alterations and the evolution of boundary-layer flow along the upper-rear surface are demonstrated by the phase-lock flow structures. It is found that the alternate blowing and suction at the slit exit serves as a perturbation to the boundary layer near the shoulder of the slit cylinder leading to a significant delay of flow separation and the flow reattachment of boundary-layer flow along the upper-rear surface of the cylinder. After perturbation, the vortex street behind a slit cylinder is more organized and stronger than that behind a baseline cylinder at Reynolds number 1000.

scholarly journals Magnetohydrodynamic cross-field boundary layer flow

1982 ◽  
Vol 5 (2) ◽  
pp. 377-384 ◽  
Author(s):  
D. B. Ingham ◽  
L. T. Hildyard
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Asymptotic Solution ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Field Boundary ◽  
Boundary Layer Equations ◽  
Mhd Boundary Layer ◽  
Blasius Boundary Layer ◽  
Layer Flow

The Blasius boundary layer on a flat plate in the presence of a constant ambient magnetic field is examined. A numerical integration of the MHD boundary layer equations from the leading edge is presented showing how the asymptotic solution described by Sears is approached.

Use of Micro Synthetic Jet Actuators for Boundary Layer Flow Control

2009 ◽  
Vol 74 ◽  
pp. 157-160
Author(s):  
Jing Chuen Lin ◽  
An Shik Yang ◽  
Li Yu Tseng
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Turbulent Flows ◽  
Boundary Layer Flow ◽  
Moving Boundary ◽  
Active Flow Control ◽  
Flow Characteristics ◽  
Synthetic Jet ◽  
Layer Flow ◽  
Active Flow

The main purpose of active flow control research is to develop a cost-effective technology that has the potential for inventive advances in aerodynamic performance and maneuvering compared to conventional approaches. It can be essential to thoroughly understand the flow characteristics of the formation and interaction of a synthetic jet with external crossflow before formulating a practicable active flow control strategy. In this study, the theoretical model used the transient three-dimensional conservation equations of mass and momentum for compressible, isothermal, turbulent flows. The motion of a movable membrane plate was also treated as the moving boundary by prescribing the displacement on the plate surface. The predictions by the computational fluid dynamics (CFD) code ACE+® were compared with measured transient phase-averaged velocities of Rumsey et al. for software validation. The CFD software ACE+® was utilized for numerical calculations to probe the time evolution of the development process of the synthetic jet and its interaction within a turbulent boundary layer flow for a complete actuation cycle.

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