signature=5cb1209670cd93d97d200f9cc5f1d775,Turbulence Structure and Wall Signature in Hypersonic Bou...

摘要：

To investigate the existence of hairpin structures at the present Reynolds and Mach numbers, a conditional average velocity field based on the presence of vortex core ( u (x , y , z )|E = λci,y * sign(ωy) > 0 ) would be suitable to examine the mean flow structure. The condition for the conditional average is chosen to be positive spanwise swirling strength motion (λci,y * sign(ωy) > 0) since hairpin vortex head is assumed to contain only positive spanwise swirling motions. However, it is computationally challenging to directly compute this conditional average. To simplify this impractical computation, linear stochastic estimation (LSE) could be used to estimate the conditional averages by minimizing the error between the conditional average and the estimate in mean-square sense.36 It has been shown that the linear estimates are surprisingly accurate and simple to form for different types of turbulent flows.36-38 In short, the conditional average of the fluctuating velocity fields ( u (x , y , z )|E(x , y , z ) ) is approximated by a linear function as Equation 1

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