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Simulation for the Thermal Effect of Micro Sensor and PIV Experimental Investigation of Intermittency in a Turbulent Flow

Author: XuZheng
Tutor: LiWanPing
School: Huazhong University of Science and Technology
Course: Fluid Mechanics
Keywords: Coherent structure Microelectromechanical systems Wall Shear Stress Micro-sensor Turbulent boundary layer Wavelet coefficients Intermittent PIV
CLC: O357.5
Type: Master's thesis
Year: 2007
Downloads: 83
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Abstract


Is generally believed that the coherent structure is the most important structures in the shear turbulence. Active control of turbulent coherent structure, the need to micro-sensor applications and enhance the understanding of the statistical properties of turbulence. The research work of this paper contains two parts: numerical simulation of of MEMS micro shear stress sensor heat transfer characteristics and turbulent multi-scale coherent structure intermittent PIV experimental study. (1) Numerical Simulation of MEMS micro-shear stress sensor wall shear stress wall turbulence is a very important physical quantities, and the development and maturation of the MEMS turbulent wall shear stress measurement and active control to provide a powerful tool. Especially for the actual processing needs, the thermal effect of the micro shear stress sensor numerical simulation. With CFD commercial software FLUENT, using a three-dimensional model, the thermal sensor in the flow, especially from the point of view of the heat exchange, by calculating the temperature field, the heat transfer efficiency and the rate of heat loss, analysis of the vacuum chamber and the air chamber in the hot-film the role of both the difference between a comparison with the case of no cavity. The calculation results show that the accession to the vacuum chamber or air cavity below the hot film sensor is very necessary. For the flow measured in the calculation results show that the temperature distribution of the vacuum chamber and the air chamber in the region of the entire calculation, and little difference in the efficiency of the heat-transfer fluid, while the cavity may be to significantly reduce the heat loss of the underlying, which improve The shearing stress sensitivity of the sensor is very necessary. Article also through the relationship of the calculated size changes with the heat transfer efficiency of the hot-film sensor size effect on the heat exchange, and provide a basis for the actual processing of thermal design of the micro-sensor. In addition, the article describes the preliminary design of the micro-shear stress sensor for fluid measurement and processing techniques. (2) The the the intermittent turbulent multi-scale coherent structure PIV experimental study of this article PIV measurements of turbulent boundary layer flow to speed plane and turbulent multi-scale coherent structures in statistical properties of experimental research. The continuous wavelet transform, to calculate the different scales, different probability density function to the position of the sub-wave coefficient as a result, the buffer has a stronger intermittent. Meanwhile, the use of wavelet coefficients quantify turbulence intermittent application and promotion of self-similar law (ESS) calculated the scaling exponent of the structure function of the wavelet coefficients. Studies have shown that the multi-scale coherent structures are extracted using the ESS scale wavelet coefficients law on the line with the Kolmogorov linear scaling law, verify that the multi-scale coherent structures turbulent boundary layer singular scaling law reasons. In addition, the use of the data of the PIV measurements gives the energy distribution of expression of flow within the plane of the wavelet coefficients, and this method is conducive to further multi-scale coherent structure identification and study the characteristics of the space plane within.

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CLC: > Mathematical sciences and chemical > Mechanics > Fluid Mechanics > Viscous fluid > Turbulence ( turbulence )
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