Closed-loop Control Of A Turbulent Boundary Layer Based On Wall Pressure Fluctuations

Drag reduction of turbulent boundary layers can contribute great economical value in engeering area.There is skin fiction generated in the surface of a transport during high velocity movement for example airplanes,vehicles,and so on.The existence of these surface friction result in the generation of heat,and damage to the surface of the transport.Due to these reasons,it is an important direction in experital dynamic flow field to reduce the drag by active control method.Turbulent boundary layers near wall is the main source of these surface friction.This work aims to research the correlation between wall pressure fluctuations and bursting events.Also,a closed-loop drag reduction control system based on wall pressure measurements is constructed.Drag reduction of turbulent boundary layers can contribute great economical value in engeering area.In turbulent boundary layer reserchments,the relationship between the variation of flow velocity and turbulent structures has received a lot of concerns.This work measures the wall pressure signals by microphone,and analyzes the correlation between busrting events in turbulent boundary layer and the variation of wall pressure signals by measuring the streamwise velocity at different location just abouve the micophone.And by experiments,it is obvious that the variation of the wall pressure signal can refelect the development of the near wall flow structures.Thus,wall pressure fluctuation is also an important parameter in turbulent boundary layers.Due to the limitless of passive control,active control has become the mainstream in turbulent boundary layer drag reduction.Active control can be divided into open-loop control and closed-loop control.Closed loop control is based on the knowlede of the generation of the surface friction.So closed-loop control can be more effective than open-loop control.What's more,there are no cases in which closed-loop drag reduction control system is based on the wall pressure fluctuations.Thus,it is meaningful to construct a closed-loop control system based on wall pressure measurements.The open loop performance of 250 mm DBD plasma actuator is measured.The results shows that in PD feedforward control system,by setting reasonable control coefficients,a proper drag reduction ratio and a 20% control efficiency improvement can be get.Thus,closed-loop drag reduction control system based on wall pressure measurements is more efficeiency than the open loop control system.