Turbulent structures, integral length scale and turbulent kinetic energy (TKE) dissipation rate in compound channel flow
| Autor: | Luís R. Roja-Solórzano, João Leal, Ricardo Gomes de Azevedo |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
Physics
Turbulence K-epsilon turbulence model 0208 environmental biotechnology 02 engineering and technology Mechanics Dissipation 01 natural sciences 010305 fluids & plasmas 020801 environmental engineering Computer Science Applications Vortex Open-channel flow Physics::Fluid Dynamics Classical mechanics Modeling and Simulation 0103 physical sciences Turbulence kinetic energy Potential flow Electrical and Electronic Engineering Instrumentation Taylor microscale |
| Zdroj: | Flow Measurement and Instrumentation. 57:10-19 |
| ISSN: | 0955-5986 |
| Popis: | In the present study, high data rate measurements were obtained for the streamwise and vertical velocity components using 2D Laser Doppler Velocimeter. The turbulent field in a straight compound-channel flow was characterized for three different uniform flow water depths, corresponding to “deep flows”, “intermediate flows” and “shallow flows” conditions. Several methodologies were studied to process the data and to obtain autocorrelation functions, integral length scale and turbulence kinetic energy (TKE) dissipation rate. The Sample and Hold method was adopted to interpolate the unevenly spaced record and calculate the autocorrelation function; the integral-stop-value 1/ e was used to estimate the integral length scale; and the TKE dissipation rate was estimated through the velocity energy spectrum. A double shear layer composed of two counter-rotating vertical oriented vortices, interacting with the secondary currents, is observed in the interface region for deep flow conditions. By decreasing the water depth, the interface region becomes dominated by a strong mixing layer of vertical oriented vortices with high TKE dissipation rate and large integral length scale, acting as a vertical wall to the weak secondary currents that develop at the main channel. The determination of the integral length scale permits to confirm the existence and the strength of these turbulence structures, unveiling the strong mixing layer as the origin of the largest integral length scales, even larger than the flow depth, and as the most efficient mechanism to redistribute turbulence generated at the bottom towards upper flow regions. Despite the high complexity of turbulence structures present in the flow, for all water depths, a linear dependence is depicted between integral length scale, TKE dissipation rate, and streamwise turbulence intensity. |
| Databáze: | OpenAIRE |
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