Near-Wall Turbulence in a Localized Puff in a Pipe
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We have performed direct numerical simulations of a transitional flow in a pipe for \(Re_m=2250\) when turbulence manifests in the form of fleshes (puffs). From experiments and simulations, \(Re_m \approx 2250\) has been estimated as a threshold when the average speeds of upstream and downstream fronts of a puff are identical (Song et al. in J Fluid Mech 813:283–304, 2017, ). The flow regime upstream of its trailing edge and downstream of its leading edge is almost laminar. To collect the velocity data, at each time instance, we followed a turbulent puff by a three-dimensional moving window centered at the location of the maximum energy of the transverse (turbulent) motion. In the near-wall region, despite the low Reynolds number, the turbulence statistics, in particular, the distribution of turbulence intensities and Reynolds shear stress becomes similar to a fully-developed turbulent pipe flow.