BURSTING AND STRUCTURE OF THE TURBULENCE IN AN INTERNAL FLOW MANIPULATED BY RIBLETS

The buffer layer of an internal flow manipulated by riblets is investi gated. The distributions of the ejection and bursting frequency from t he beginning to the middle part of the buffer layer, together with hig h moments of the fluctuating streamwise velocity, u', and its time der ivative are reported. The profiles of the ejection and bursting freque ncy are determined and compared using three single point detection sch emes. The effect of the riblets on the bursting mechanism is found con fined in a localized region in the buffer layer. The multiple ejection bursts are more affected than the single ejection bursts. The skewnes s and flatness factors of the u' signal are larger in the manipulated layer than in the standard boundary layer. That, also holds true for t he flatness factor of the time derivative, but the Taylor and Liepman scales are not affected. The spectrum of the u' signal is altered at t he beginning part of the viscous sublayer.