Flow characteristics in low-speed wind tunnel contractions: Simulation and testing

A numerical and experimental study was conducted to characterize flow through low-speed wind tunnel contractions. The simulations were carried out using an incompressible, two-dimensional flow solver based on finite volume scheme, predicting flow along the core, and at immediate vicinity of the wall of three pre-selected wall-shape contractions. The numerical results have been validated against experimental data obtained, utilizing laser-Doppler anemometer (LDA). Particular attentions have been given to the bulk flow velocity, the centerline mean velocity, the centerline velocity fluctuations, the uniformity of the mean velocity distribution at contraction’s exit, and to the mean pressure coefficient. The experimentally determined mean-pressure coefficient values along the centerline and at contraction exit were found to be similar to those predicted numerically. The fifth-order polynomial contraction showed, however, good flow characteristics at the exit plane with small non-uniformity when compared to both the two-cubic arcs and the Witoszynski second-order polynomial contractions. It was therefore adopted for the Cottbus Large pipe (CoLaPipe) facility at the Department of Aerodynamics and Fluid Mechanics (LAS), BTU-Cottbus-Sefftenberg. Keywords: Wind tunnel, Contraction, Numerical simulations, Experimental flow

Experimental evaluation of the mean momentum and kinetic energy balance equations in turbulent pipe flows at high Reynolds number

In light of recent data from hot-wire anemometry and laser Doppler velocimetry, this article explores experimentally the momentum balance and kinetic energy production in fully developed turbulent pipe flow for shear Reynolds numbers in the range from two pipe facilities. It has become common practice to indirectly deduce the Reynolds shear stress via the mean flow data and the mean-momentum balance whenever the simultaneous measurements of the streamwise and wall-normal velocity fluctuations can not be performed precisely. The current assessment underlines, however, the importance of measuring the Reynolds shear stress directly, and the friction velocity independently from the mean-velocity profile to ascertain the quality of the data when utilising the momentum balance. The present analysis also reinforces the universality of the viscous stress gradient to the Reynolds shear stress gradient in the wall vicinity up to the inner limit of the logarithmic layer. The new set of the experimental data shows that Panton's stress function reproduces the measured Reynolds shear stress and kinetic energy production in turbulent pipe flows over a wide Reynolds number range to a high degree

Wavenumber dependence of very large-scale motions in ciclope at 4800 \ue2\u89\ua4 Re\ucf\u84 \ue2\u89\ua4 37,000

The present work aims at investigating the very large-scale structures of turbulent pipe flow in CICLoPE at high Reynolds numbers. According to recent studies, some open questions remain to be answered to identify accurate sizes of these turbulent structures in pipe flow. The CICLoPE facility has been therefore utilized, providing an opportunity to approach high Reynolds number flows with high enough resolution in terms of the viscous length scale, allowing us to investigate the behavior of such turbulent structures. Meandering structures, usually referred as VLSM (very large-scale motions), have been identified with claimed extension up to 20R, where R is the pipe radius