Computation of high speed turbulent boundary-layer flows using thek-ε turbulence model

1985 ◽  
Vol 5 (1) ◽  
pp. 81-97 ◽  
Author(s):  
A. Liakopoulos
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulence Model ◽  
High Speed ◽  
Boundary Layer Flows

An Experimental Investigation on the Characteristics of Turbulent Boundary Layer Flows Over a Dimpled Surface

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Wenwu Zhou ◽  
Yu Rao ◽  
Hui Hu
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Surface Pressure ◽  
High Speed ◽  
Boundary Layer Flows ◽  
Piv Measurement ◽  
Measurement Results ◽  
Flow Features

An experimental investigation was conducted to quantify the characteristics of the turbulent boundary layer flows over a dimpled surface in comparison to those over a conventional flat plate. In addition to measuring surface pressure distributions to determine the friction factors of the test plates and to map the surface pressure inside the dimple cavity, a high-resolution digital particle image velocimetry (PIV) system was used to achieve detailed flow field measurements to quantify the characteristics of the turbulent boundary layer flows over the test plates and the evolution of the unsteady vortex structures inside the dimple cavity at the middle of the dimpled test plate. It was found that the friction factor of the dimpled plate would be about 30–80% higher than that of the flat plate, depending on the Reynolds number of the test cases. In comparison with those over a conventional flat surface, the flow characteristics of the turbulent boundary layer flows over the dimpled surface were found to be much more complicated with much stronger near-wall Reynolds stress and higher turbulence kinetic energy (TKE) levels, especially in the region near the back rims of the dimples. Many interesting flow features over the dimple surface, such as the separation of oncoming boundary layer flow from the dimpled surface when passing over the dimple front rim, the formation and periodic shedding of unsteady Kelvin–Helmholtz vortices in the shear layer over the dimple, the impingement of the high-speed incoming flow onto the back rim of the dimple, and the subsequent generation of strong upwash flow in the boundary flow to promote the turbulent mixing over the dimpled surface, were revealed clearly and quantitatively from the PIV measurement results. The quantitative measurement results are believed to be the first of its nature, which depict a vivid picture about the unique flow features over dimpled surfaces and their correlations with the enhanced heat transfer performance reported in previous studies.

An Improved K-ω Model for High Speed Flows

2012 ◽  
Vol 629 ◽  
pp. 593-600
Author(s):  
Jing Yuan Liu ◽  
Zeng Hui Zhao
Keyword(s):  
Boundary Layer ◽  
Turbulence Model ◽  
High Speed ◽  
Correction Term ◽  
Plate Boundary ◽  
Experimental Results ◽  
Tvd Scheme ◽  
Boundary Layer Flows ◽  
Calculation Results ◽  
Improved Model

An improved K-ω model, which allows for compressible corrections, is proposed in this paper. Numerical scheme was established utilizing the improved Total Variation Diminishing (TVD) scheme and applying implicit scheme to the negative source terms of the turbulence model. Hypersonic flat-plate boundary-layer flows and hypersonic compression ramp flows marked with separation, reattachment and shock/boundary layer interactions are then computed. Comparisons between the computational results, the experimental results and the semi-empirical formulations show that the compressible correction term of the K-ω turbulence model is a pressure-dilatation correlation. In addition, for flow with separation and without separation, calculation results of wall pressures, friction coefficients and wall heat transfer rate distributions using the improved model and established scheme agree better with the experimental results than that using the original K-ω model.

scholarly journals Passive bristling of mako shark scales in reversing flows

2018 ◽  
Vol 15 (147) ◽  
pp. 20180473 ◽  
Author(s):  
Kevin T. Du Clos ◽  
Amy Lang ◽  
Sean Devey ◽  
Philip J. Motta ◽  
Maria Laura Habegger ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
High Speed ◽  
Scale Up ◽  
Control Mechanisms ◽  
Flow Conditions ◽  
Boundary Layer Flows ◽  
Mako Shark ◽  
Shortfin Mako

Shark skin has been shown to reduce drag in turbulent boundary layer flows, but the flow control mechanisms by which it does so are not well understood. Drag reduction has generally been attributed to static effects of scale surface morphology, but possible drag reduction effects of passive or active scale actuation, or ‘bristling’, have been recognized more recently. Here, we provide the first direct documentation of passive scale bristling due to reversing, turbulent boundary layer flows. We recorded and analysed high-speed videos of flow over the skin of a shortfin mako shark, Isurus oxyrinchus . These videos revealed rapid scale bristling events with mean durations of approximately 2 ms. Passive bristling occurred under flow conditions representative of cruise swimming speeds and was associated with two flow features. The first was a downward backflow that pushed a scale-up from below. The second was a vortex just upstream of the scale that created a negative pressure region, which pulled up a scale without requiring backflow. Both flow conditions initiated bristling at lower velocities than those required for a straight backflow. These results provide further support for the role of shark scale bristling in drag reduction.

Three-dimensional instantaneous structure of a shock wave/turbulent boundary layer interaction

2009 ◽  
Vol 622 ◽  
pp. 33-62 ◽  
Author(s):  
R. A. HUMBLE ◽  
G. E. ELSINGA ◽  
F. SCARANO ◽  
B. W. van OUDHEUSDEN
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Turbulent Boundary Layer ◽  
High Speed ◽  
Large Scale ◽  
Three Dimensional ◽  
Reflected Shock Wave ◽  
Layer Interaction ◽  
Reflected Shock ◽  
Boundary Layer Interaction

An experimental study is carried out to investigate the three-dimensional instantaneous structure of an incident shock wave/turbulent boundary layer interaction at Mach 2.1 using tomographic particle image velocimetry. Large-scale coherent motions within the incoming boundary layer are observed, in the form of three-dimensional streamwise-elongated regions of relatively low- and high-speed fluid, similar to what has been reported in other supersonic boundary layers. Three-dimensional vortical structures are found to be associated with the low-speed regions, in a way that can be explained by the hairpin packet model. The instantaneous reflected shock wave pattern is observed to conform to the low- and high-speed regions as they enter the interaction, and its organization may be qualitatively decomposed into streamwise translation and spanwise rippling patterns, in agreement with what has been observed in direct numerical simulations. The results are used to construct a conceptual model of the three-dimensional unsteady flow organization of the interaction.

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