Experimental Sdudy Of Adverse Pressure Gradient Turbulent Boundary Layer

The adverse pressure gradient(APG)turbulent boundary layer(TBL)is a common phenomenon in nature and industrial production,for example,on curved surfaces such as wing and impeller.The most common APG effect is to cause the TBL to separate,and then produce various bad situations.Since the underwater vehicle and submarine also have curved surfaces in their tail,so there is naturally an APG effects which will separate the boundary layer.On the one hand,the boundary layer separation is accompanied by vortex detachment,which impacts the tail propeller.On the other hand,the resistance of the vehicle and submarine will also be increased.Therefore,it is very important to study the properties of the APG TBL.According to the above background,this thesis aimed to the study of the APG TBL.First,the experimental set-up was designed and calibrated.The set-up was verified through the distribution of the wall pressure coefficient along the streamwise direction under the zero pressure gradient(ZPG).Optimal angel was found by adjusting flap for different Reynolds numbers,which made the stagnation point located in the tip of leading edge.It was found that the measurement positions in the current work were not under the influence of the flap inclined.Subsequently,the APG environment was manufactured by adjusting the flexible ceiling above the tested part and APG calibration of the set-up was completed.The results of the APG calibration showed that the set-up could adjust the boundary layer dimensionless pressure gradient coefficient?(?=?*/?w·(dp/dx))up to 9.73,which is a strong APG recognized by the universal standard in the academic field.So the device has sufficient APG adjustment capabilities.In order to accurately measure the velocity distribution of the viscous sublayer and calculate the wall shear stress at higher Reynolds number(Re_x>1×10~6),a long-distance micro-PIV system was explored and improved.The final results showed that 37 velocity vectors could be measured by long-distance micro-PIV under the condition of the minimum sublayer thickness(?120?m)involved in allexperiments of this article.The average minimum resolvable spatial scale is about 5?m under all conditions.Finally,the hot-wire signals of TBL were analyzed.The distribution of turbulence statistics and their relationship at four streamwise measurement positions which located in the fully developed section of the APG TBL were studied under three Reynolds numbers.Based on PIV data,the streamwise evolution and distribution of vortex packets and evolution of the relative strength of ejection events and sweep events Q2/Q4 in APG TBL at the same Reynolds number were studied too.It has been found that there were vortex packets structures with rising angle of 29°in the APG TBL,which remains unchanged with the increase of the dimensionless pressure gradient parameter?.This phenomenon is different from the literature.In Q2/Q4 distribution,a third peak was found near the boundary layer edge,which has not been reported.