1. Motivation and objectives In many industrial devices such as heat exchangers, piston engines, or propulsion systems strong temperature gradients arise in the near wall region even if the characteristic Mach number is close to zero. A strong coupling exists between momentum and energy equations caused by variations in the fluid properties, and the classical wall models for incompressible flow...

Direct numerical simulations are performed to contrast turbulent boundary layers over a concave wall without and with free-stream turbulence. Adverse pressure gradient near the onset of curvature leads sharp decrease in skin friction intermittent separation. The presence turbulence reduces probability reverse flow, accelerates recovery layer downstream zero-pressure region, sustained appreciabl...

The Galerkin finite element method is used to solve the three dimensional continuity, momentum and energy equations for laminar Newtonian and power-law model non-Newtonian flow through horizontal circular tube. The governing equations are non-dimensionalized with respect to specific variables and converted into algebraic equations using appropriate elements. To accelerate convergence a combinat...

This paper presents experimental measurements of the approach and rebound of a particle colliding obliquely with a wall in a viscous fluid. Steel and glass particles 12.7mm in diameter were used. The experiments were performed using a thick Zerodur wall (a glass-like material) with various mixtures of glycerol and water. Normal and tangential coefficients of restitution were defined from the ra...

It is shown that a local bend of a nanowire is a source of pinning potential for a transversal head-to-head (tail-to-tail) domain wall. Eigenfrequency of the domain wall free oscillations at the pinning potential and the effective friction are determined as functions of the curvature and domain wall width. The pinning potential originates from the effective curvature-induced Dzyaloshinsky-like ...

Two simple feedback control laws for drag reduction are derived by applying a suboptimal control theory to a turbulent channel flow. These new feedback control laws require pressure or shear-stress information only at the wall, and when applied to a turbulent channel flow at Reτ = 110, they result in 16–22% reduction in the skin-friction drag. More practical control laws requiring only the loca...

A simple expression is derived of the componential contributions that different dynamical effects make to the frictional drag in turbulent channel, pipe and plane boundary layer flows. The local skin friction can be decomposed into four parts, i.e., laminar, turbulent, inhomogeneous and transient components, the second of which is a weighted integral of the Reynolds stress distribution. It is r...

As air is injected into a flowing liquid, the resultant bubble characteristics depend on the properties of the injector, near-wall flow, and flowing liquid. Previous research has shown that near-wall bubbles can significantly reduce skin-friction drag. Air was injected into the turbulent boundary layer on a test section wall of a water tunnel containing various concentrations of salt and surfac...

A semi-empirical model is presented that describes the development of a fully developed turbulent boundary layer in the presence of surface roughness with length scale ks that varies with streamwise distance x. Interest is centred on flows for which all terms of the von Kármán integral relation, including the ratio of outer velocity to friction velocity U+ ∞ ≡ U∞/uτ , are streamwise constant. F...

We show that the classic laws of the mean-velocity profiles (MVPs) of wall-bounded turbulent flows-the 'law of the wall,' the 'defect law' and the 'log law'-can be predicated on a sufficient condition with no manifest ties to the MVPs, namely that viscosity and finite turbulent domains have a depressive effect on the spectrum of turbulent energy. We also show that this sufficient condition is c...