Based on an experimental investigation carried out in a low-speed test facility at the Berlin University of Technology, this paper describes the formation of separation bubbles under steady and periodic-unsteady main flow conditions. The aim of the investigation was to understand the mechanism of separation, transition, and reattachment, and the effect of main flow unsteadiness on it. Separation bubbles for various main flow conditions were generated over a large flat plate, which experienced a similar pressure distribution to that on the suction surface of blades in turbomachines. The pressure distribution was generated by a contoured wall opposite the plate. Aimed at separating the effect of the velocity and the turbulence wake, this paper considers only the influence of the velocity wake. To this effect, a rotating flap was mounted downstream of the test section to produce periodic oscillations of the main flow. The overall flow field under steady main flow conditions was obtained by hot-wire measurements. Pressure taps were used to measure the pressure distribution over the plate. The Reynolds number effects were determined and compared to the measurement results in the literature. Results for periodic-unsteady separation bubbles are shown using different Strouhal numbers, oscillation amplitudes, and Reynolds numbers. Ensemble-averaged mean velocity profiles and the ensemble-averaged rms velocity profiles are used to demonstrate the development of the periodic boundary layer. Time–space diagrams are plotted to show the development of the periodic-unsteady boundary layers. The characteristic instability frequencies in the free shear layer are identified. The impact of the major parameters, Strouhal number and amplitude, on the bubble formation are discussed. [S0889-504X(00)01204-6]
Based on an experimental investigation carried out in a low speed test facility at the Berlin University of Technology, this paper describes the formation of separation bubbles under steady and periodic-unsteady main flow conditions. The aim of the investigation was to understand the mechanism of separation, transition and reattachment and the effect of main flow unsteadiness on it. Separation bubbles for various main flow conditions were generated over a large flat plate, which experienced a similar pressure distribution to that on the suction surface of blades in turbomachines. The pressure distribution was generated by a contoured wall opposite the plate. Aimed at separating the effect of the velocity and the turbulence wake, this paper considers only the influence of the velocity wake. To this effect, a rotating flap was mounted downstream of the test section to produce periodic oscillations of the main flow. The overall flow field under steady main flow conditions was obtained by hot-wire measurements. Pressure taps were used to measure the pressure distribution over the plate. The Reynolds number effects were determined and compared to the measurement results in the literature. Results for periodic-unsteady separation bubbles are shown using different Strouhal numbers, oscillation amplitudes and Reynolds numbers. Ensemble averaged mean velocity profiles and the Ensemble averaged rms velocity profiles are used to demonstrate the development of the periodic boundary layer. Time-space diagrams are plotted to show the development of the periodic-unsteady boundary layers. The characteristic instability frequencies in the free shear layer are identified. The impact of the major parameters, Strouhal number and amplitude, on the bubble formation are discussed.
The effects of unsteadiness both on high-response dynamic measurements and on time-averaged measurements with slow-response probes are analytically investigated separately from the response characteristics of the measuring system. The approach is based on physical similarity and dimensional analysis. The potential errors from flow unsteadiness and the major parameters which influence the measurement results are discussed. In the case of five sensor spherical probes a quantitative investigation for inviscid, incompressible, irrotational flow is carried out with the help of potential theory.
Laminar-turbulent transition flow phenomena on a flat plate in a low-speed wind tunnel at different Reynolds numbers were studied numerically. The flow calculation is based on an inviscid/boundary layer interaction method with modified Abu-Ghannam/Shaw(AGS) transition criterion. The test section has non-symmetrical contoured walls, and the plate is located biased the bottom side with a height ratio of 26:14. In test case of steady flow, a laminar-turbulent transition takes place and a small separation bubble occurs on the upper side of the plate, when the inlet Reynolds number is as small as 0.631x10 -6. The predicted transition location agrees well with that of the test results, but the separation bubble is hardly to see from the calculated velocity profiles though the printed data of velocity in this region do show the negative values. The further numerical predictions with different Reynolds numbers corresponding to the incoming flow velocities show that when the Reynolds number is greater than 1.379x10 6, the separation bubble does not occur, which is coincident with the experimental results. The influence of the side wall geometry on the transition on the plate is also studied.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.