Mixing Characteristic Analysis And Flow Control Of Shear Flow

Shear flow has high value of scientific research for its importance in nature and engineering applications.In the aerospace field,shear flow is a major feature of these flows,whether it is the wing boundary layer,engine jet or aircraft wake.An important research of aircraft aerodynamic design is to improve the overall performance of aircraft by controlling the shear flow.The main research object of this paper is the shear flow formed downstream of a flat plate with different configurations of trailing edges.By comparing the different characteristics of development state and coherent structures of shear flow,changes of the flow parameters in each stage of the formation and development of shear flow is analyzed,and the relationship between the coherent structures and the mixed characteristics of shear flow is studied,which provides some references for the control of shear flow.In this paper,the work is mainly based on wind tunnel test combines with numerical simulation and data analysis methods.The construction of the experimental shear flow model is based on the analysis of the shear flow formed by the multi-element airfoils wake,slot flow and main airfoil boundary layer,and shear flow of the tandem airfoils,This paper focused on the analysis of shear layer mixing characteristics of different models,and studied the method of identifying the spatial structures of shear flow,summarized the correlation between shear flow and coherent structures and provided the method of controlling mixing of shear flow which is verified by experiments.In summary,the main work of this paper is as follows:1.This paper analyzed how the front airfoil wake affected the flow field and the aerodynamic force on the rear airfoil in the case that the distance between two airfoils had various values in the streamwise or the normal direction in the steady flow.While in the unsteady flow,the effect of the front airfoil wake on the flow field and the aerodynamic force on the rear airfoil in the case of different amplitudes and frequencies of the front airfoil’s motion was studied.The influence of above parameters on the aerodynamic performance of the tandem airfoils was summarized,and a flow control method based on the front airfoil wake was proposed.2.Based on the study of complex shear flow around multi-element airfoils,a flow control method was proposed to improve the aerodynamic performance of multi-element airfoils by optimizing the trailing edge(TE in short)of slat,such as changing the shape of the TE of slat or adding jet flows at different flow rates or directions on the TE of slat.This paper summarized the relationship between the development as well as the state of mixing of the shear flow above the main airfoil and the aerodynamic characteristic of multi-element airfoils.3.Based on the studies of shear flows developed after the slat with different TE configurations,this paper designed an incompressible shear flow experiment in which the data were acquired by hot-wire probe.In this experiment,the specific impact of different TE shapes of flat plate on the change of the thickness of the shear flow in the streamwise and the normal direction was studied in detail.Reasonable suggestions for the shear flow control based on the analysis of the development of shear flow on different spatial planes under different TE conditions.4.Energy analysis based on wavelet analysis method was used to identify the large-scale coherent structure in shear flow.This paper analyzed the relationship between the scale of the large-scale coherent structure and the thickness of the shear flow.A method for controlling the thickness of the shear flow and promoting the mixing of two streams was proposed based on the above analysis.