This is an experimental and theoretical study of a laminar separation bubble the associated linear stability mechanisms. Experiments were performed over flat plate kept in wind tunnel, with imposed pressure gradient typical aerofoil that would involve bubble. The was characterized by measurement surface-pressure distribution streamwise velocity using hot-wire anemometry. Single component anemometry also used for detailed transition dynamics. It found so-called dead-air region front portion...

The SARS-CoV-2 is transmitted not only through coughing, but also breathing, speaking or singing. We perform direct numerical simulations of the turbulent transport potentially infectious aerosols in short conversations, involving repetitive phrases separated by quiescent intervals. estimate that buoyancy effects due to droplet evaporation are small, and neglect them. A two-way conversation shown significantly reduce aerosol exposure compared with a relative monologue one person silence...

Clouds are the largest source of uncertainty in climate science, and remain a weak link modeling tropical circulation. A major challenge is to establish connections between particulate microphysics macroscale turbulent dynamics cumulus clouds. Here we address issue from latter standpoint. First show how create bench-scale flows that reproduce variety cumulus-cloud forms (including two genera three species), track complete cloud life cycles--e.g., "cauliflower" congestus dissipating fractus....

Cumulus clouds, which are among the largest sources of uncertainty in climate change science and tropical circulation, have to-date resisted numerous attempts made during last six decades to unravel their cloud-scale dynamics. One major reason has been lack a convincing fluid-dynamical model difficulty making repeatable measurements an inherently transient flow. This article summarizes recent work showing that cumulus-type f lows can be generated laboratory by releasing volumetric heat into...

Abstract Laminar separation bubbles are thought to be highly non-parallel, and hence global stability studies start from this premise. However, experimentalists have always realized that the flow is more parallel than commonly believed, for pressure-gradient-induced bubbles, why linear theory has been successful in describing their early stages of transition. The present experimental/numerical study re-examines important issue finds base such a bubble becomes nearly due strong-interaction...

Direct numerical simulation has been carried out on one attached and two separated boundary layer flows (involving small large separation) under the influence of an adverse pressure gradient. A unified picture pre-transitional for three cases provided that reveals a “mixed-mode” instability, involving contribution from instability waves streamwise streaks. time-frequency analysis transitional velocity signals performed which shows as Reynolds number decreases, character time traces evolves...

Here, we present some interesting new results on the linear modal stability of Couette–Poiseuille flow (CPF), by numerically solving Orr–Sommerfeld equation within temporal framework. We provide a mechanistic explanation to well-known result that upper plate movement causes progressive stabilization CPF. The energy budget reveals appearance region negative production with movement, which is located near has higher relative velocity in direction bulk flow. This contribution integral term,...

The aim of the present work is to investigate spectral structure a rapidly distorted boundary layer that develops on flat plate in presence localised patch roughness or/and grid-generated freestream turbulence. We observe that, at certain distance downstream exhibits bimodal shape energy spectrum streamwise velocity fluctuations, similar found fully-turbulent relatively high Reynolds numbers. physical mechanism gives rise low-wavenumber peak spectrum, which represents long motions or...

Abstract

Rayleigh’s inflection point theorem and Fjortoft’s provide necessary conditions for inviscid temporal instability of a plane parallel flow. Although these theorems have been assumed to hold in the spatial framework also, rigorous theoretical basis such an application is not available literature. In this paper, we by carrying out formal analysis Rayleigh equation. We prove that, under certain satisfied wide class flows, Fjortoft are applicable stability problem also. This work thus fills...

(2021). Direct Numerical Simulation of a Moist Cough Flow using Eulerian Approximation for Liquid Droplets. International Journal Computational Fluid Dynamics: Vol. 35, CFD and COVID-19. Guest Editor: Tony Saad, pp. 778-797.

Entrainment in cumulus clouds has been a subject of investigation for the last sixty years, and continues to be central issue current research. The development laboratory facility that can simulate cloud evolution enables us shed light on problem. apparatus purpose is based physical model flow as plume with off-source diabatic heating dynamically similar effect latent-heat release natural clouds. We present critical review experimental data so far obtained such facilities variation...

Anomalous entrainment in cumulus clouds has been a topic of investigation over many decades the past. Its importance stems from fact that rate is one major inputs to several cumulus-parameterization schemes. Recently Narasimha et al. (PNAS; 2011) have successfully simulated large-scale dynamics cumulus-cloud flows laboratory and provided mechanistic explanation for observed cumulus-entrainment anomalies. They showed favourable comparison dilution-related quantity (called 'purity') between...

Abstract In this work, we characterize the early stages of transition in a flat-plate boundary layer caused by two types surface roughness: distributed roughness (a strip 24-grit emery) and isolated cylindrical element). Towards this, carry out extensive particle image velocimetry (PIV) measurements. The consists range grit heights introduces broad disturbances downstream it. pre-transitional region, both cause steady streaks, which for latter case show lack spanwise symmetry. This is...

Pathogens like the SARS-CoV-2 are transmitted not only through violent expiratory events coughing, but also routine activities breathing/speaking/singing. We perform direct numerical simulations of turbulent transport potentially infectious aerosols in short conversations. It is shown that a two-way conversation significantly reduces aerosol exposure compared to relative monologue by one person and silence other. This because interaction jets ejected from mouth each speaker produce...