Experimental Study On The Lateral Velocity Derivative In A Turbulent Boundary Layer

Flow is a common physical phenomenon in the natural world,and boundary layer generated when the fluid move around objects such as aircraft,ships and cars.The skin friction drag mainly exists in the turbulent boundary layer.It's helpful to control the turbulent boundary layer by studying the structures and the mechanism of turbulent boundary layer,which make contribution to reduce the skin friction drag and save lots of energy.The average energy dissipation rate is a very important physical quantity in the turbulent flow.The average energy dissipation rate is also play an essential role in modeling turbulent flow and testing turbulent theory.In the near wall region of turbulent boundary layer,the mean square of the lateral velocity derivative(7)(8)2?u ?y account for 80% of the total average turbulent energy dissipation rate ?.And the mean square of the lateral velocity derivative has been used to estima te the energy dissipation rate in the near wall region of the turbulent boundary layer.A parallel hot wire probes can provide the relatively accurate measurements.However,it will cause electromagnetic noise or low spatial resolution if the separation of parallel hot wire probes is too small or too large.Therefore,the selection of an appropriation separation between parallel hot wires has become a new problem.In this paper,the lateral velocity derivative is measured by using a variable separation parallel hot wires device in flat plate turbulent boundary layer,and the influence of different separation between parallel hot wires on measurement is investigated,and the range of appropriation separation is also found.The measurement is taken place in different positions of turbulent boundary layer and the separation of parallel hot wire probe is changed from 0.2 mm to 3.1 mm.And the range of separation can be obtain for measuring the value of lateral velocity derivative accurately in the wall region.New substitution formulas are provided for approximating average energy dissipation rate by using mean square of streamwise and lateral velocity derivative in near wall region and log law region,respectively.In this paper,a method to measure the vertical distance between hot wires and the wall by using a Total station device is designed,and another method utilizing linear region to estimate the position of hot wires is prove valid.An appropriation separation between parallel hot wire is selected to measu re the open-loop control boundary layer,and the mechanism of drag reduce by wall vibration is studied.