A study of the Blasius wall jet

Abstract

A plane wall-jet flow is numerically investigated and compared to experiments. The measured base flow is matched to a boundary-layer solution developing from a coupled Blasius boundary layer and Blasius shear layer. Linear stability analysis is performed, revealing high instability of two-dimensional eigenmodes and non-modal streaks. The nonlinear stage of laminar-flow breakdown is studied with threedimensional direct numerical simulations and experimentally visualized. In the direct numerical simulation, an investigation of the nonlinear interaction between twodimensional waves and streaks is made. The role of subharmonic waves and pairing of vortex rollers is also investigated. It is demonstrated that the streaks play an important role in the breakdown process, where their growth is transformed from algebraic to exponential as they become part of the secondary instability of the twodimensional waves. In the presence of streaks, pairing is suppressed and breakdown to turbulence is enhanced.

Breaking bore: Physical observations of roller characteristics

“…The data sets exhibited a quasi-normal distribution, yielding (X − X median ) /d 1 = 0.145 on average at a given time. The pseudo-periodic shape of the roller toe perimeter implied the existence of non-linear structures, streamwise vortices and streaks, somehow similar to those observed in plane mixing layers and wall jets [13,14]. The existence of streamwise structures was complementary to the occurrence of organised structures in the shear layer seen in Fig.…”

Direct numerical simulation of a plane turbulent wall-jet including scalar mixing

“…Streamwise vortices are added in the upper shear layer. This disturbance type was found by Levin et al 19 to play an important role in plane-jet transition. The amplitude of the added vortices is 0.01U in .…”

“…Wernz and Fasel 16,17 employed DNS to investigate instability mechanisms in a transitional wall-jet. The breakdown of a finite-aspect-ratio wall-jet was studied by Visbal et al 18 Recently, Levin et al 19 studied the laminar breakdown of a wall-jet using linear analysis and DNS. In an extension to that work, Levin 20 used a larger computational box to obtain averaged turbulence statistics.…”

Non-modal stability of round viscous jets

“…The optimal-to-single mode energy ratio has not exceeded 2.5. The algebraic instability of a wall jet was investigated by Levin et al (2005). It has been found that the energy of stationary optimal disturbances (with zero frequency) is three orders of magnitude larger than that of the first mode with the same initial energy.…”