The paper presents the results of a detailed experimental examination of fully developed asymmetric flow between parallel planes. The asymmetry was introduced by roughening one of the planes while the other was left smooth; the ratio of the shear stresses at the two surfaces was typically about 4:1.The main emphasis of the research has been on establishing the turbulence structure, particularly in the central region of the channel where the two dissimilar wall flows (generated by the smooth and rough surfaces) interact. Measurements have included profiles of all non-zero double and triple velocity correlations; spectra of the same correlations at several positions in the channel; skewness and flatness factors; and lateral two-point space correlations of the streamwise velocity fluctuation.The region of greatest interaction is characterized by strong diffusional transport of turbulent shear stress and kinetic energy from the rough towards the smooth wall region, giving rise, inter alia, to an appreciable separation between the planes of zero shear stress and maximum mean velocity. The profiles of length scales of the larger-scale motion are, in contrast to the turbulent velocity field, nearly symmetric. Moreover, it appears that at high Reynolds numbers the small-scale motion may in many respects be treated as isotropic.

Fully developed asymmetric flow in a plane channel

Heat and fluid flow in rectangular solar air heater ducts having transverse rib roughness on absorber plates

Turbulent convective heat transfer from rough surfaces with two-dimensional rectangular ribs

The work presents the design relations and recommendations on the use of a number of efficient methods of heat transfer enhancement in differnt-geometry channels

Heat Transfer Enhancement in Heat Exchangers

The local time-averaged velocity, the mixed-mean velocity, and the friction factor for fully turbulent flow between parallel plates and in round tubes and concentric circular annuli can be expressed in terms of integrals of the turbulent shear stress, The pressure distribution across a channel can similarly be expressed in terms of an integral of normal stresses. These formulations, which are simple and exact, can be integrated numerically using experimental data, compyted values, or correlating equations for turbulent stresses. Their greatest merit, however, may arise from the insight they provide with respect to the contributions of the fluctuating components of the velocity. For example, for concentric circular annuli such a formulation identifies a difference between the locations of the maximum in the velocity and the zero in the total shear stress. This difference, which has been overlooked in most experimental and semitheoretical investigations, introduces an error of unknown but possibly significant magnitude into all of the results. It also precludes the application of the mixing-length, eddy viscosity and k - ϵ models.

Turbulent flow in channels in terms of turbulent shear and normal stresses

Friction factor measurements in a rectangular channel with walls of identical and non-identical roughness

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Friction factor measurements in a rectangular channel with walls of identical and non-identical roughness