Kemal Hanjalic

Elliptic blending model: A new near-wall Reynolds-stress turbulence closure

A new approach to modeling the effects of a solid wall in one-point second-moment (Reynolds-stress) turbulence closures is presented. The model is based on the relaxation of an inhomogeneous (near-wall) formulation of the pressure–strain tensor towards the chosen conventional homogeneous (far-from-a-wall) form using the blending function ?, for which an elliptic equation is solved. The approach preserves the main features of Durbin’s Reynolds-stress model, but instead of six elliptic equations (for each stress component), it involves only one, scalar elliptic equation. The model, called “the elliptic blending model,” offers significant simplification, while still complying with the basic physical rationale for the elliptic relaxation concept. In addition to model validation against direct numerical simulation in a plane channel for Re? = 590, the model was applied in the computation of the channel flow at a “real-life” Reynolds number of 106, showing a good prediction of the logarithmic profile of the mean velocity.

Wall imprint of turbulent structures and heat transfer in multiple impinging jet arrays

Thermal imprint and heat transfer on the target surface in multiple impinging jet arrays have been investigated in conjunction with flow pattern and large-scale eddy structure. Surface temperature was measured with liquid crystal thermography (LCT) in a range of jet configurations with hexagonal and in-line orifice arrangements for different combinations of distances between the orifices

A new form of the elliptic relaxation equation to account for wall effects in RANS modeling

s/D_m\,{=}\,2\hbox{--}6

A direct-numerical-simulation-based second-moment closure for turbulent magnetohydrodynamic flows

and between the orifice plate and the impingement surface

Modeling the response of turbulence subjected to cyclic irrotational strain

H/D_m\,{=}\,3\hbox{--}10

Reorganization of turbulence structure in magnetic Rayleigh-Benard convection: a T-RANS study

(where

Tackling complex turbulent flows with transient RANS

D_m

Prediction of Cascade Flows With Innovative Second-Moment Closures

is the orifice diameter). The hexagonal arrangement was considered with two different orifice shapes: sharp-edged and contoured. For selected configurations, the distribution of Nusselt number and its peculiarities were analysed in relation with the underlying eddy structure educed by proper orthogonal decomposition (POD) of the snapshots of fluid velocity measured with particle image velocimetry (PIV). Owing to the breakdown of the jets, heat transfer deteriorates with increasing orifice-to-plate distance. The jet interaction and breakdown become more severe as the jets are placed closer to each other. The large-scale eddies originating from the jet-edge shear layers grow as they are convected towards the impingement plate. Eddies of sizes between 0.2 and 0.3 orifice diameters are shown to break up the jets and cause mixing of fresh and spent fluid, lowering the beneficial temperature gradient. In some configurations, an asymmetric flow pattern is generated with embedded weak eddies on only one side of the diagonal symmetry line, which is reflected in an asymmetrical heat transfer distribution on the impingement plate. For

Numerical insights into magnetic dynamo action in a turbulent regime

H/D_m\,{>}\,4

Impinging Jet Cooling of Wall Mounted Cubes

, the Nusselt number shows peak values in and around the jet impingement centres, but relatively uniform distribution of turbulence kinetic energy with local negative energy production close to the impingement surface.