The Damping of the Large Wave-Number Disturbances in a Free Boundary Layer Flow

1965 ◽  
Vol 20 (1) ◽  
pp. 164-169 ◽  
Author(s):  
Kanefusa Gotoh
Keyword(s):  
Boundary Layer ◽  
Free Boundary ◽  
Boundary Layer Flow ◽  
Wave Number ◽  
Large Wave ◽  
Layer Flow ◽  
Large Wave Number

Vortex Instability in Buoyancy-Induced Flow over Inclined Heated Surfaces in Porous Media

1979 ◽  
Vol 101 (4) ◽  
pp. 660-665 ◽  
Author(s):  
C. T. Hsu ◽  
Ping Cheng
Keyword(s):  
Boundary Layer ◽  
Inclination Angle ◽  
Boundary Layer Flow ◽  
Heated Surface ◽  
Wave Number ◽  
Heated Plate ◽  
Local Similarity ◽  
Linear Temperature ◽  
Vortex Instability ◽  
Layer Flow

A linear stability analysis is performed for the study of the onset of vortex instability in free convective flow over an inclined heated surface in a porous medium. The undisturbed state is assumed to be the steady two-dimensional buoyancy-induced boundary layer flow which is characterized by a non-linear temperature profile. By a scaling argument, it is shown that the length scales of disturbances are smaller than those for the undisturbed boundary layer flow, thus, confirming the so-called “bottling effects” whereby the disturbances are confined within the boundary layer. By neglecting the lowest order terms in the three-dimensional disturbances equations, the simplified equations are solved based on the local similarity approximations, wherein the disturbances are assumed to have a weak dependence in the streamwise direction. The resulting eigenvalue problem is solved numerically. The critical parameter and the critical wave number of disturbances at the onset of vortex instability are computed for different prescribed wall temperature distribution of the inclined surface. It is found that the larger the inclination angle with respect to the vertical, the more susceptible is the flow for the vortex mode of disturbances; and in the limit of zero inclination angle (i.e., a vertical heated plate) the flow is stable for this form of disturbances.

scholarly journals BOUNDARY LAYER FLOW AND SAND TRANSPORT UNDER FULL SCALE SURFACE WAVES

2011 ◽  
Vol 1 (32) ◽  
pp. 4 ◽  
Author(s):  
Jolanthe J.L.M. Schretlen ◽  
Jan S. Ribberink ◽  
Tom O'Donoghue
Keyword(s):  
Boundary Layer ◽  
Surface Waves ◽  
Boundary Layer Flow ◽  
Oscillatory Flow ◽  
Full Scale ◽  
Sand Transport ◽  
Sheet Flow ◽  
Large Wave ◽  
Layer Flow ◽  
Scale Surface

Existing models for wave-related (cross-shore) sand transport are primarily based on data from oscillatory flow tunnel experiments. However, theory and former experiments indicate that flow differences between full scale surface waves and oscillatory flow tunnels may have a substantial effect on the net sand transport. In this paper, high resolution measurements of boundary layer flow characteristics, sheet-flow layer sediment concentrations and net sand transport rates under full scale surface waves are presented. These experiments were performed in a large wave flume (GWK) for different wave conditions with medium (D50 = 0.25 mm) and fine (D50 = 0.14 mm) sand. It is shown that, especially under sheet-flow conditions, small wave induced net currents are of large importance for the total sand transport rates under these conditions.

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