Shear-modified Sub-grid Model With Applications To The Study Of Turbulence

Sub-grid model is the critical problem of large eddy simulation (LES). A shear-modified sub-grid model is presented and test with and without blow-suction is held. The result shows that the model presented here is fit for turbulent flow field with and without blow-suction.Then, turbulent channel flow with different Reynolds number is simulated using the method of LES with this model. And statistic characteristic of near-wall turbulence is researched. Furthermore, the blow-suction near the wall is considered. The phase relationship of Reynolds stress and Mean Rate-of-Strain is studied in spatial periodic turbulent flow field.The conclusion of statistic characteristic about near-wall turbulence is as follows.(1) The pressure difference given, the mean velocity profile is lower and lower along with full shape and longer log region of profile when the Reynolds number becomes bigger, and the profile is more and more consistent with log law or power law when the Reynolds number becomes bigger.(2) The energy of velocity fluctuations, Reynolds stress and rms velocity with different Reynolds number are of resemblance to some extent. The curves tend to superposition both near the wall in wall coordinates and in channel center with global coordinates. The energy of velocity fluctuations and rms velocity come to be a constant in channel center.(3) The relation between the peak values and the position of the peak of Reynolds stress and energy of velocity fluctuations and Reynolds number is provided along with formula. The distribution of Reynolds stress and energy of velocity fluctuations is offered in parameter style with use of subsection and full function according to the distribution in lower Reynolds number. When the distributions of Reynolds stress and energy of velocity fluctuations with lower Reynolds number is known, those items with higher Reynolds number can be gained based on parameters. The conclusion of relationship between the phase of Reynolds stress and the phase of Mean Rate-of-Strain is as follows.(4) There is phase difference between the Reynolds stress and Mean Rate-of-Strain. And phase difference should be considered in eddy viscosities in model theory(5) The variation of phase difference can be divided into four region, wall control region, wall main control region, main control region of out flow, control region of out flow. In wall control region, the phase difference is rapidly increased. In wall main control region, the increase of phase difference is slow down, and the maximum value is gotten. In main control region of out flow, the effect of out flow strengthens, and the phase difference slowly descends. In control region of out flow, the variation of phase difference is slow.(6) When the wave number becomes bigger, the width of wall control region remains invariable, the width of wall main control region and main control region of out flow become narrowed, the width of control region of out flow increases evidently.(7) In the range of Reynolds numbers investigated, the variation of phase difference between Reynolds stress and Mean Rate-of-Strain becomes similar along normal direction of channel. The phase difference changes with Reynolds numbers observably. The cures move towards wall in global coordinates with bigger Reynolds numbers. However, there is no move near the wall in wall coordinates. The area near peak of phase difference becomes broad with Reynolds number increasing.(8) The variation of phase difference between Reynolds stress and Mean Rate-of-Strain obeys the rules when the amplitude of blow-suction is small. When the amplitude of blow-suction is greater then a threshold, nonlinear disturbance occurs. So the reaction of the phase of Reynolds stress and the phase of Mean Rate-of-Strain is different, and the phase difference between Reynolds stress and Mean Rate-of-Strain will also change.