Preliminary Rotor Wake Measurements with a Laser Velocimeter.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER
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An experimental investigation using a laser velocimeter LV was conducted in the Langley 4- by 7-Meter Tunnel to determine rotor wake characteristics. The purpose of the project was to define the effect of various fuselage widths and rotor-fuselage spacings on time-averaged and detailed time-dependent rotor wake velocity characteristics. Definition of time-dependent velocity characteristics was attempted with the LV by associating a rotor azimuth position with each velocity measurement. The results were discouraging in that no apparent time-dependent velocity characteristics could be discerned from the LV measurements. Since the LV is a relatively new instrument in the rotor wake measurement field, the cause of this lack of periodicity is as important a result as the basic research objectives. An attempt was made to identify the problem by simulated acquisition of LV-type data for a predicted rotor wake velocity time history. Power spectral density and autocorrelation function estimation techniques were used to further substantiate the conclusion that the primary cause of the lack of time-dependent velocity characteristics was the nonstationary flow condition generated by the periodic turbulence level that currently exists in the open-throat configuration of the wind tunnel.
- Lasers and Masers
- Test Facilities, Equipment and Methods