We describe the first DNS-based measurement of the complete mean response of a turbulent channel flow to small external disturbances. Space-time impulsive perturbations are applied at one channel wall, and the linear response describes their mean effect on the flow field as a function of spatial and temporal separations. The turbulent response is shown to differ from the response a laminar flow...

Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding ra...

Cystic fibrosis (CF) is a chronic progressive pulmonary disorder caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene. A CF lung is generally characterized by obstructed airflow to an extent that leads to destruction of airway wall support structure. Airway resistance, resulting from both laminar and turbulent flow, is an important mechanical factor contrib...

A controlled ex-vivo study of a simple, sinusoidally oscillating flow in a rigid, constant-area, smooth tube, has produced significant insight into the laminar-turbulent transition phenomenon. The development of turbulence was studied by analyzing the dynamic characteristics of the transition process; i.e., the velocity, growth rate, and intermittency which describe the generation and propagati...

using the highly recommended numerical techniques, a finite element computer code is developed to analyse the steady incompressible, laminar and turbulent flows in 2-d domains with complex geometry. the petrov-galerkin finite element formulation is adopted to avoid numerical oscillations. turbulence is modeled using the two equation k-ω model. the discretized equations are written in the form o...

In the present paper active separation control of a transitional laminar separation bubble is investigated by means of direct numerical simulations. The specific influence of different forcing amplitudes and disturbance modes on the size and shape of the laminar separation bubble are illustrated. These consist of steady and unsteady twoand three-dimensional Tollmien– Schlichting-(TS)-like bound...

The new semi-experimental method for simulation of the turbine flow meters rotation in the transitional flow has been developed. The method is based on the experimentally established exponential low of changing of dimensionless relative turbine gas meter rotation frequency and meter inertia time constant. For experimental evaluation of the meter time constant special facility has been developed...

Lower-branch traveling waves and equilibria computed in pipe flow and other shear flows appear intermediate between turbulent and laminar motions. We take a step towards connecting these lower-branch solutions to transition by deriving a numerical method for finding certain special disturbances of the laminar flow in a short pipe. These special disturbances cause the disturbed velocity field to...

The transition to turbulence in pipe flow does not follow the scenario familiar from RayleighBenard or Taylor-Couette flow since the laminar profile is stable against infinitesimal perturbations for all Reynolds numbers. Moreover, even when the flow speed is high enough and the perturbation sufficiently strong such that turbulent flow is established, it can return to the laminar state without a...