Time Accurate Simulations of High-Alpha Aerodynamics for Pitching Delta Wings
Abstract
Fighter airplanes are designed to transiently fly at very high angles of attack. The types of maneuvers they do involve high pitch rates and flight at incidences beyond the static stall angle of attack. The performance of fighters in high angle-of-attack maneuvers is often reached thanks to the use of a delta wing. The aerodynamics of these wings at incidence is characterized by the formation of a pair of strong leading-edge vortices on the leeward side of the wing. The vortices create a zone of high flow velocity with low surface pressures on the wing producing an additional lift compared to classical rectangular shapes. At very high incidence, however, the vortex flow breaks down, a zone of recirculation with a turbulent wake appears, and the lift decreases. During maneuvers, the same phenomena occur but the flow has to adapt to the moving planform and thus time-lags are observed in the dynamic response. This study seeks to reproduce the dynamic formation, development, and burst of the vortex that forms on the leeward side of a 70 degree swept delta wing pitching in sinusoidal oscillations around its 40% chord point. Emphasis is placed on the prediction of the hysteresis loops that form in the aerodynamic loads history, but the visualization of the unsteady flow around the wing also is introduced. The freestream Mach number for all the computations (both Euler and Navier-Stokes) is set to 0.2 while the mean angle of attack is changed between 12 degrees, 22 degrees, and 38 degrees for oscillations with a semi-amplitude varying between 3 degrees and 18 degrees. The moving grid approach implemented in the flow solver NSMB is used to reproduce the motion of the wing, and the time-dependent flow equations are integrated with the dual time-stepping method. In addition, a method for co-processing the simulation and visualization of the flow field is presented using flow feature extraction to reduce the amount of data saved. (12 figures, 26 refs.)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2003
- Accession Number
- ADA419103
Entities
People
- A. Rizzi
- Y. Le Moigne
Organizations
- Royal Institute of Technology