| An active drag reduction control method is implemented in this work by streamwise slits periodic blowing in turbulent boundary layers.By comparing the control performance of different actuators,the optimal control parameters are obtained.Under the engineering feasibility,based on former research and improved by increasing the length to 35mm and 50mm of the slits,self-designed actuators are used.Hot-wire anemometry is used in the experiment.The maximum local drag reduction is measured at x+=33.3.With the optimal control parameters,the effecting control area downstream then can be measured.The experiment results show that under the same flow rate,the higher the control frequency is,the better local control performance can be obtained.When the control frequency increases to 300Hz,the drag reduction ratio of three actuators are all 70%.With the optimal control parameters,drag recovery is measured downstream the actuator.There are 11 spanwise slits in each actuator in early stage of the research.The effective control area of the 35mm-length-slit actuator is x+=350,and for 50mm-slit length actuator,it is x+=467,which is the same as the original 20mm-length actuator with 9 spanwise slits.Then the number of the slits was increased to 31.The drag recovery was measured under the same output velocity with same control frequency 300Hz.The results show that the number of the slits has no influence on the effective control area of 20mm-length-slit actuator.The local drag reduction rate of the 35mm actuator increased obviously.And its control area is expanded to x+=600 downstream.This indicates that increasing the number of 35mm slits can improve drag reduction rate and control area.But it is not the same as the 50mm-length-slit actuator.The recovery of the actuator the length of whose slits is 20mm is also measured at different flow rate.The results shows that the decreasing of flow results in the decreasing of the local drag reduction rate but not control area. |
PDF Full Text Request