Active Control And Heat Transfer Enhancement Mechanism Of Turbulent Coherent Structure

The coherent structure of turbulent boundary is the most discoverable and the most interesting problem of turbulence in the last several decades. Heat transfer, diffusion, friction drag and noise induced by turbulent coherent structure arouse broad attention in industrial and environmental problems. From the view point of saving power and protecting the environment, it is strongly desired to develop efficient turbulence control techniques for drag reduction and heat transfer augmentation.On the basis of the exiting investigation of coherent structure of turbulent boundary, the article applies the method combining numerical simulation and the experiment to investigate the effect of active control on heat transfer and flow resistance.Flow in the rectangle channel is simulated by virtue of large eddy simulation. The pressure field, temperature field, velocity field, vortex field and flow structure are attained. The variational process of turbulence coherent structure recurs.Via the analysis of statistical data, six active control models which may be effective in heat transfer enhancement and drag reduction are gained, namely the direction of control velocity is a slope of -30°,-45°,-90°,-135°,-150°,90°with the direction of streamwise. Then different active control models are simulated and wall friction coefficient and heat transfer coefficient are respectively attained. Through analyzing the results, the relationship between coherent structure of turbulent flow and heat transfer and flow drag is opened out.The computational results show that -45°and -30°can change the velocity field,the temperature field and the vortex field effectively and enhance heat transfer and reduce the flow drag, and -135°,-150°and 90°can change the velocity field, the temperature field and the vortex field ineffectively and reduce the flow drag and do not enhance heat transfer. In conclusion, the general effect (Nu/Nu0)(/f/f0)1/3 of five cases,namely -45°,-30°,-135°,-150°and 90°are biger than one.In order to validate results of numerical simulation, an experiment on the heat transfer and flow drag in the rectangular channel is done. The conclusion of the experiment is uniform with that of numerical simulation.