Accession Number : ADA625675


Title :   Topic 1.1.2, Unsteady Aerodynamics: Time-Varying Compressible Dynamic Stall Mechanisms Due to Freestream Mach Oscillations


Descriptive Note : Final rept. 1 Oct 2011-20 Sep 2014


Corporate Author : OHIO STATE UNIV COLUMBUS


Personal Author(s) : Gregory, James W


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a625675.pdf


Report Date : 31 Dec 2014


Pagination or Media Count : 88


Abstract : The objective of this study is to investigate the effects of time-varying, compressible flow on rotorcraft dynamic stall. The problem was studied in an unsteady transonic wind tunnel and partitioned into three segments to facilitate understanding: pitch oscillations in a steady freestream, investigating unsteady effects (reduced frequency) and compressibility effects (Mach number); fixed pitch in a modulated freestream, studying various pre- and post-stall angles with fluctuating Mach number; and oscillations of both angle of attack and Mach number, studying the coupled effects and the importance of phasing between the two. The impact of compressibility on the traditional dynamic stall process was evaluated, with higher Mach numbers (and corresponding increased compressibility effects) changing the character of dynamic stall on the SSC-A09 from leading-edge to a trailing-edge phenomenon. Mach oscillations on a fixed-angle airfoil were found to have significant hysteresis at pre-stall angles, and substantial unsteadiness (periodic pressure fluctuations) in the post-stall regime. Coupled pitch and Mach oscillations showed that periods of flow acceleration have a stabilizing effect on the dynamic stall event.


Descriptors :   *COMPRESSIBLE FLOW , *OSCILLATION , *ROTARY WING AIRCRAFT , *UNSTEADY AERODYNAMICS , ACCELERATION , AIRFOILS , ANGLES , COUPLING(INTERACTION) , DYNAMICS , FREE STREAM , HYSTERESIS , LEADING EDGES , MACH NUMBER , MODULATION , PITCH(MOTION) , STABILIZATION , STALLING , STEADY STATE , TRAILING EDGES , TRANSONIC WIND TUNNELS , VARIABLE PRESSURE , VARIATIONS , WIND TUNNELS


Subject Categories : Aerodynamics
      Helicopters
      Test Facilities, Equipment and Methods


Distribution Statement : APPROVED FOR PUBLIC RELEASE