EXPERIMENTAL RESEARCH ON COMPLEX EDDY VISCOSITY MODELING IN TURBULENT BOUNDARY LAYER
湍流边界层复涡黏模式的实验研究

There are different forms of eddy viscosity modeling adopted in the modeling ofcoherent structures in outer field of turbulent boundary layer, which are explained by the theory ofhydrodynamic instability. Likewise, a question whether it should be real or complex number alsooccurs in general modeling theories used to periodical flow in many engineering, such as the flowin turbine. The objective of this experiment is to clarify this question. A self-designed mechanicalvibration device is used to generate periodical disturbance in outer field of turbulent boundary layerin a water channel. At the same time, an X style hot film probe and anemometer are employed tomeasure in the downstream area. According to the eddy viscosity modeling on coherent structure,a phase-average method is applied to the disturbed fiuctuating velocity signal in term of a fiducialfrequency, which is the frequency of the periodical large-scale structure in fluctuating velocitycaptured by power spectrum analysis. Then we have examined the form of eddy viscosity of theperiodic large-scale structure in turbulent boundary layer by comparing the phase value of thelarge scale strain rate and Reynolds stress according to the periodic disturbance. It is found that,in flow direction component, a phase shift exists between the large-scale strain rate and Reynoldsstress according to the periodic disturbance, which is an unconsidered important factor in the mostof turbulence modeling finally induced to eddy viscosity. We have also found that this phase shiftmay decrease with increasing distance to the wall along normal direction.