Non-Linear Evolution of Point-Source Disturbances in an Adverse Pressure Gradient Laminar Boundary Layer

Abstract

Localized disturbances evolving in a transitioning boundary layer (BL) represent much more realistically the natural transition process than the periodic, in space and time, disturbances commonly studied. They also present a much more difficult task for prediction and simulation. The harmonic point source (HPS) is simple, since only one continuous spectrum is present (i.e. in the spanwise wave number). A pulsed localized disturbance complicates the analysis by generating also a continuous frequency (or streamwise wave number) spectrum. Even the linear stage of HPS evolution in Blasius flow is not successfully predicted (Mack and Herbert, 1995), while discrepancies are partly attributed to experimental uncertainties, unknown input spectra and non-parallel effects. Indeed, the importance of controlling and documenting the base flow conditions for stability experiments can not be underestimated. The effect of boundary layer growth on the wave pattern prediction is in some dispute. Studying disturbance evolution in an adverse pressure gradient, where the boundary layer growth is significantly faster than in Blasius flow, hopefully will supply the relevant data for comparing parallel and non-parallel calculations at a high discrimination level.KeywordsWave PacketAdverse Pressure GradientLocalize DisturbanceLinear Stability TheoryDisplacement ThicknessThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.