Turbulent characteristics and rotation correction of wall function in rotating channel with high local rotation parameter

The turbulent fluctuation and the rotation correction of wall function law are investigated in the entrance section of a rotating channel. The one-dimensional hot wire probe and the X-type probe are utilized to measure the boundary layer at four streamwise stations. Through the analysis on the boundary layer near the leading side and trailing side, it is found that the turbulent fluctuation is promoted in the trailing side whereas suppressed in the leading side. This difference is attributed to the Coriolis instability near the trailing side. In addition, considering the local rotation parameter Rc, whose maximum absolute value is 0.014, is larger than that in previous research, whose maximum value is 0.007, the whole process of the relaminarization is captured. To understand this phenomenon better, the effects of the generation term and the Coriolis term in the transport equation of the Reynolds stress are discussed. In addition, the rotation correction of the viscous-Coriolis region and the Coriolis region are discussed, a new revising method for the wall function is proposed.

Variable slip window technology in transition detection on pitching airfoil

In the pitching motion,the unsteady transition and relaminarization position plays an important role in the dynamic characteristics of the airfoil.In order to facilitate the computer to automatically and accurately calculate the position of the transition and relaminarization,a Variable Slip Window Technology(VSWT)suitable for airfoil dynamic data processing was developed using the S809 airfoil experimental data in this paper and two calculation strategies,i.e.,global strategy and single point strategy,were proposed:global strategy and single point strategy.The core of the VSWT is the selection of the window function h and the parameters setting in the h function.The effect of the VSWT was evaluated using the dimensionless pulse strength value(INB),which can be used to evaluate the signal characteristics,of the root mean square(RMS)value of the fluctuating pressure.It is found that:the h function characteristics have a significant influence on the VSWT.The suitable functions are Hn function constructed in this paper and step function.For the left boundary of the magnified area,the step function can obtain the largest INB value,but the robustness is not good.The H1 function(Gaussian-like function,n=1)can show higher robustness while ensuring a large INB value.The two computing strategies,which are single point strategy and global strategy,have their own advantages and disadvantages.The former strategy,that is the single point strategy,can achieve a higher INB value,but the RMS magnification at the feature position needs to be known in advance.Although the INB value obtained by the latter strategy,that is the global strategy,is slightly smaller than the calculation results of the former strategy,it is not necessary to know the RMS magnification at the feature position in advance.So the global strategy has better robustness.The experimental data of NACA0012 airfoil was used to further validate the developed VSWT in this paper,and the results show that the VSWT developed in this paper can still double the INB value of the transition/relaminarization position.The VSWT developed in this paper has certain practicability,which is convenient for the computer to automatically determine the transition/relaminarization characteristics.

Study of riblet drag reduction for an infinite span wing with different sweep angles

This paper studies the riblet drag reduction effect for an infinite swept wing under a low Reynolds number using a large-eddy simulation.The results show that the drag reduction ratio is not linear under different sweep angles.The maximum drag reduction ratio in this study is 9.5%for a wing with a 45°sweep angle.The local surface streamline angle and turbulence quantities are calculated to analyze the drag reduction mechanism.The results demonstrate that the riblets considerably suppress the Reynolds stresses above the wing upper surface,while the turbulence kinetic energy in the near wake is increased.A possible relaminarization phenomenon is observed at the middle part of the wing.Quasi-two-dimensional flow structures are observed near the wall,and a peak frequency is considered as the dominant frequency of the region.

吹气比对外凸曲壁湍流再层流化现象的影响

再层流化是一种边界层加速时湍流向层流或类层流反向转捩的流动现象,它能降低边界层抵抗逆压梯度的能力.为了揭示主动射流方法调控湍流再层流化现象的机理,本文采用大涡模拟方法,研究了不同吹气比对马赫3超声速湍流绕外凸曲壁膨胀加速时再层流化现象的影响.结果表明,无控制时,膨胀加速显著降低了大尺度拟序结构和湍动能等湍流特征.施加主动射流控制后,再层流化现象被有效抑制.同时,研究还发现,吹气比在湍流再层流化流动控制中起到重要作用.在相同的射流动量比和静压比条件下,吹气比越大,主动射流抑制再层流化现象的效果越明显.