When a laminar boundary layer separates because of an adverse streamwise pressure gradient, the flow is subject to increased instability with respect to smallamplitude disturbances. Laminar–turbulent transition occurs under a rapid three-dimensional (3D) development within the separated shear layer. When the following turbulent boundary layer reattaches, a laminar separation bubble is formed. T...

long-throated flumes are measurement structures often used in water and wastewater systems to determine the flow discharge. the head-discharge relationship of long-throated flumes is traditionally determined following the critical flow theory and the boundary layer concept. after a review of the traditional approach and an analysis of the approximate assumptions of the boundary layer approach, ...

A laminar boundary layer separates in a region of adverse pressure gradient, undergoes transition, and finally the turbulent boundary layer reattaches, forming a laminar separation bubble (LSB). Laminar-turbulent transition within such a LSB is investigated by means of Laser-Doppler-Anemometry (LDA), Particle Image Velocimetry (mono PIV and stereoscopic PIV (SPIV)) and direct numerical simulati...

Occurrence of laminar separation bubbles on solid walls of an elliptic cylinder has been simulated using a recently developed transitional model for boundary layer flows. Computational method is based on the solution of the Reynolds averaged Navier-Stokes (RANS) equations and the eddy-viscosity concept. Transitional model tries to simulate streamwise fluctuations, induced by freestream turbulen...

We define turbulent-turbulent spot as a local concentration of vortices with high level of swirling strength originating from hairpin packet in a turbulent boundary layer. We also define bypass transition in the narrow sense as the breakdown of the Blasius boundary layer beneath freestream homogeneous isotropic turbulence with an initial amplitude of 1 to 4 percent. We present evidence for the ...

This communication presents the results and conclusions of an experimental study of the near-separation region of a single-stream shear layer. The momentum thickness at separation (x=0) was θ0 = 9.6mm, with Reynolds number Reθ =4650. Boundary layer separation was caused by a sharp 90◦ edge. Detailed singleand multipoint measurements of the velocity field were acquired at the streamwise location...

In turbomachinery flows, the boundary-layer can remain laminar up to 70% of the chord length, due to a relatively low local Reynolds number on the blade. The high free-stream turbulence intensity penetrates into the laminar boundary-layer by the combined action of turbulence diffusion and pressure fluctuations, and triggers the transition process to a turbulent state. This transition process is...

The boundary layer on a circular cylinder undergoes a transition to turbulence at, approximately, Re=2 x 105. This is accompanied with a significant reduction in drag. Using a stabilized finite element formulation, we have conducted two-dimensional computations for flow past a cylinder using a very fine mesh close to it. It has been shown by researchers earlier that the genesis and formation of...

Direct numerical simulation (DNS) is used to study laminar to turbulent transition induced by a discrete hemispherical roughness element in a high-speed laminar boundary layer. The simulations are performed under conditions matching the experiments of Danehy et al. (AIAA Paper 2009–394, 2009) for free-stream Mach numbers of 3.37, 5.26 and 8.23. It is observed that the Mach 8.23 flow remains lam...