Investigation of flow separation in a transonic-fan linear cascade using visualization methods
An extensive experimental study into the nature of the separated flows on the blade suction surface of modern transonic fans is described in this paper. The study was a subtask of a larger experimental effort focused on blade flutter excited by flow separation in the blade tip region. The tip sections of airfoils on transonic fan blades are designed for precompression and consequently they differ from sections on the rest of the blade. The blade tip section was modeled by a low aspect ratio blade and therefore most of the blade tested was exposed to the secondary flow effects. The aim of this work was to supply reliable data on flow separation on transonic fan blades for validation of future analytical studies. The experimental study focused on two visualization techniques: surface flow visualization using dye oils and schlieren (and shadowgraph) flow visualization. The following key observations were made during the study. For subsonic inlet flow, the flow on the suction surface of the blade was separated over a large portion of the blade, and the separated area increased with increasing inlet Mach number. For the supersonic inlet flow condition, the flow was attached from the leading edge up to the point where a bow shock from the upper neighboring blade imposed on the blade surface. Downstream, there was a separated flow region in which air flowed in the direction opposite the inlet flow. Finally, past the separated flow region, the flow reattached to the blade surface. For subsonic inlet flow, the low cascade solidity resulted in an increased area of separated flow. For supersonic flow conditions, the low solidity resulted in an improvement in flow over the suction surface.
Refurbishment and Testing Techniques in a Transonic Ludwieg Tunnel
Although cryogenic wind tunnels are typically used in industry for transonic testing, Ludwieg tunnels with high charge tube pressures can also produce unit Reynolds numbers high enough to match inight conditions. A brief timeline of transonic Ludwieg tunnel development is presented that shows how it was nearly selected for full-scale construction to compliment the National Transonic Facility. Having recently been refurbished, an overview of the unique high Reynolds number facility at UT Arlington is presented. Currently, experiments with the facility have been conducted using a combination of porous and solid walls with a half-span NACA 0012 model. Surface ow visualization techniques are discussed for this high Reynolds number, short duration facility. Future development e orts are presented to keep the facility suitable for current transonic testing topics.
Full potential solution of transonic quasi-three-dimensional flow through a cascade using artificial compressibility
A reliable method is presented for calculating the flowfield about a cascade of arbitrary two-dimensional airfoils. The method approximates the three-dimensional flow in a turbomachinery blade row by correcting for streamtube convergence and radius change in the throughflow direction. 12 refs.