arXiv subjects

Trinh Khanh Tuoc

Publications and source records attributed to Trinh Khanh Tuoc.

7 recordsLinked to original sources

arXiv2010

Reflections on a Penetration Theory of Turbulent Heat Transfer

This paper discusses a modified penetration theory where the time scale for the momentum wall layer is based on the onset of ejections from the wall but the time scale for the thermal layer is based on the unsteady state diffusion of heat from the wall into the streamwise flow, not the renewal of heat from eddies penetrating the wall layer. A method for the determination of the thickness of the thermal wall layer has been developed. The theory correlates adequately experimental data for both the thickness of the thermal wall layer and the Nusselt number. Key words: Heat transfer, penetration theory, turbulence, time scales.

physics.flu-dyn↗

arXiv2010

A Theoretical Closure for Turbulent Flows Near Walls

This paper proposes a simple new closure principle for turbulent shear flows. The turbulent flow field is divided into an outer and an inner region. The inner region is made up of a log-law region and a wall layer. The wall layer is viewed in terms of the well known inrush-sweep-burst sequence observed since 1967. It is modelled as a transient laminar sub-boundary layer, which obeys the Stokes solution for an impulsively started flat plate. The wall layer may also be modelled with a steady state solution by adding a damping function to the log-law. Closure is achieved by matching the unsteady and steady state solutions at the edge of the wall layer. This procedure in effect feeds information about the transient coherent structures back into the time-averaged solution and determines theoretically the numerical coefficient of the logarithmic law of the wall The method gives a new technique for writing accurate wall functions, valid for all Reynolds numbers, in computer fluid dynamics (CFD) programmes. Keywords: Reynolds equations, modelling, closure technique, wall layer, log-law, CFD.

physics.flu-dyn↗

arXiv2010

On the Non Specific Nature of Classical Turbulence Statistics

The classical statistics of turbulence are shown to be not specific to turbulence and can be derived from a solution for recurring unsteady state viscous flow. Care must be exercised in using them to make deductions about turbulence structures and mechanisms. The conditionally averaged statistics, particularly involving the velocities of the ejections in the burst phase, are more distinctive of turbulence. Key words: Turbulence statistics, classical, conditional average, probability density function, energy spectrum

physics.flu-dyn↗

arXiv2010

The Fourth Partial Derivative In Transport Dynamics

A new fourth partial derivative is introduced for the study of transport dynamics. It is a Lagrangian partial derivative following the path of diffusion, not the path of convection. Use of this derivative decouples the effect of diffusion and convection and simplifies the analysis of transport processes.

math-ph↗

arXiv2010

Additive Layers: An Alternate Classification of Flow Regimes

It is argued that ejections of wall fluid in the bursting process disturb the flow beyond the wall layer and result in the emergence of two new layers in the flow field: the law of the wake and log-law layers. The wall layer represents the extent of penetration of viscous momentum into the main flow and remains constant once it has reached a critical value at the end of the laminar regime. The identification of the three flow regimes: laminar, transition and fully turbulent is conveniently achieved by monitoring the emergence of these three layers

physics.flu-dyn↗

arXiv2010

A Zonal Similarity Analysis of Velocity Profiles in Wall-Bounded Turbulent Shear Flows

It is argued that there are three distinct zones in a wall bounded turbulent flow field dominated by three completely different mechanisms: - An outer region where the velocity profile is determined by the pressure distribution - A highly active wall layer dominated by a sequence of inrush-sweep and ejections, and - An intermediate region well described by the traditional logarithmic law proposed by independently Millikan and Prandtl. The log-law and the wall layer are sometimes referred to as the inner region. Under these conditions, a unique set of normalisation parameters cannot possibly apply to all three zones. The inner region can be more successfully represented by normalising the distance and velocity with the values of these scales at the edge of the wall layer since they are shared by both the wall layer and the log-law region. The application of this similarity analysis has successfully collapsed extensive published data for the inner region covering a range of Reynolds numbers from 3000 to 1,000,000 in a variety of geometries including cylindrical pipes, external boundary layers on flat plates, recirculation regions behind a sudden channel expansion, converging rectangular channels and oscillating pipe flows into a unique curve. The normalisation also collapsed drag reducing flow involving ribblets, power law fluids and viscoelastic fluids onto the standard Newtonian curve.

physics.flu-dyn↗

arXiv2009

A theory of turbulence. Part 1:Towards solutions of the Navier-stokes equations

In this visualisation the instantaneous local velocity is expressed in terms of four components to capture the development of and interactions between coherent structures in turbulent flows. It is then possible to isolate the terms linked with each major type of structure and identify the corresponding subsets of the Navier-Stokes equations that are easier to solve than the full version. Each of these subsets applies to a domain in the flow field not a flow regime. The traditional statistics of turbulence are shown to be not specific to turbulent flow. In particular the Reynolds stresses, the probability density function, the dissipation, the production and the energy spectrum are obtained from one subset associated with unsteady "laminar" flow. The evidence also indicates that the Kolmogorov scale does not represent an eddy size and more importantly that it does not require the assumption of local isotropy. Applications of this visualisation include a proposal for a theoretical closure of the Reynolds equations, the collapse of velocity and skin friction profiles for Newtonian and non-Newtonian fluid flows in all geometries into unique master curves. A new partial derivative is introduced that decouples the effect of diffusion and convection simplifying the mathematical solution of subsets of the NS equations with implications for a more efficient generation of computational fluid dynamics packages. Finally the consequences to turbulent heat and mass transfer are examined.

physics.flu-dyn↗