Browsing by Author "Schaeffler, Norman W."

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    All The King's Horses: The Delta Wing Leading-Edge Vortex System Undergoing Vortex Breakdown: A Contribution to its characterization and Control under Dynamic Conditions
    Schaeffler, Norman W. (Virginia Tech, 1998-04-20)
    The quality of the flow over a 75 degree-sweep delta wing was documented for steady angles of attack and during dynamic maneuvers with and without the use of two control surfaces. The three-dimensional velocity field over a delta wing at a steady angle of attack of 38 degrees and Reynolds number of 72,000 was mapped out using laser-Doppler velocimetry over one side of the wing. The three-dimensional streamline and vortex line distributions were visualized. Isosurfaces of vorticity, planar distributions of helicity and all three vorticity components, and the indicator of the stability of the core were studied and compared to see which indicated breakdown first. Visualization of the streamlines and vortex lines near the core of the vortex indicate that the core has a strong inviscid character, and hence Reynolds number independence, upstream of breakdown, with viscous effects becoming more important downstream of the breakdown location. The effect of cavity flaps on the flow over a delta wing was documented for steady angles of attack in the range 28 degrees to 42 degrees by flow visualization and surface pressure measurements at a Reynolds number of 470,000 and 1,000,000, respectfully. It was found that the cavity flaps postpone the occurrence of vortex breakdown to higher angles of attack than can be realized by the basic delta wing. The effect of continuously deployed cavity flaps during a dynamic pitch-up maneuver of a delta wing on the surface pressure distribution were recorded for a reduced frequency of 0.0089 and a Reynolds number of 1,300,000. The effect of deploying a set of cavity flaps during a dynamic pitch-up maneuver on the surface pressure distribution was recorded for a reduced frequency of 0.0089 and a Reynolds number of 1,300,000 and 187,000. The active deployment of the cavity flaps was shown to have a short-lived beneficial effect on the surface pressure distribution. The effect on the surface pressure distribution of the varying the reduced frequency at constant Reynolds number for a plain delta wing was documented in the reduced frequency range of 0.0089 to 0.0267. The effect of the active deployment of an apex flap during a pitch-up maneuver on the surface pressure distribution at Reynolds numbers of 532,000, 1,000,000, and 1,390,000 were documented with reduced frequencies of 0.0053 to 0.0114 with flap deployment locations in the range of 21° to 36° . The apex flap deployment was found to have a beneficial effect on the surface pressure distribution during the maneuver and in the post-stall regime after the maneuver is completed.
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    Heat transfer from a spherical surface by jet impingement: an experimental study
    Schaeffler, Norman W. (Virginia Polytechnic Institute and State University, 1988)
    Methods for the removal of heat from a sphere, via jet impingement by single and multiple jets was documented experimentally. Average heat transfer rates from a sphere maintained at constant temperature, by means of an internal electronic heater, and subjected to single or multiple jet impingements were obtained and related to the exit conditions of the impinging air jet(s) and to geometric parameters. The heat transfer rate was found to be insensitive to small changes in geometry. The heat transfer rate was found to increase with an increase in mass flow rate. The impingement of two jets was found not to be as efficient as a single jet using the same mass flow rate. Compressibility was found to decrease the heat transfer rate at high values of the Mach number. Attempts to increase the heat transfer rate by increasing the entrainment of the jet by acoustic or mechanical excitation or by the use of an elliptic orifice meet with no success. The decrease in velocity due to the increase in entrainment cancelled any benefit that was gained by increasing the entrainment of the jet.