Abstract
We demonstrated the evolution of grid turbulence under the action of a stable, linear, temperature gradient with smoke-wire method. The experiment was carried out in a large, open circuit, low speed wind tunnel 0.91×0.91 m2 and 9.14 m in length specially designed for the study of stratified turbulence. The smoke was generated by heating a thin nichrome wire coated with heavy-weight oil and the facility to take the pictures was controlled by a computer for the consistant shots. The temperature gradient, formed at the entrance to the plenum chamber of the tunnel by means of an array of 72 horizontal, differentially heated elements was 0°C/m for the unstratified case and 55°C/m for the stratified case where a Brunt-Väisälä frequencyN was 1. 3s −1. The grid mesh sizeM was 2.54 cm and the mean velocityU was fixed at 2.8 m/s for both cases. Thus the mesh Froude numberFr M =U/(NM) was ∞ and 84.8 for the unstratified and stratified case respectively. We show that there are distinct differences in the evolution of the flow for the stable case, especially, the vertical motion decays much more rapidly than for the neutral (unstratified) case. No evidence of internal wave motion is found from the flow visualization pictures.
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Yoon, K. Flow visualization of grid generated turbulence under stable thermal stratification. KSME Journal 8, 414–421 (1994). https://doi.org/10.1007/BF02944713
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DOI: https://doi.org/10.1007/BF02944713