Parametric Time-Dependent Navier-Stokes Computations for a YAV-8B Harrier in Ground Effect

Extended Abstract for the 40 'hAerospace Sciences Meeting & ExhibitTo be held in Reno, NV, January 14-17, 2002Parametric Time-Dependent Navier-Stokes Computationsfor a YAV-8B Harrier in Ground EffectNeal M. Chaderjian* and Shishir Pandya, tNASA Ames Research Center, Moffett Field, California 94035andJasim Ahmad _ and Scott Murman °ELORET, Moffett Field, California 94035IntroductionThe Harrier Jump Jet has the distinction of being the only powered-lift aircraft in the freeworld to achieve operational status and to have flown in combat.I This V/STOL aircraft cantake-off and land vertically or utilize very short runways by directing its four exhaust nozzlestowards the ground. Transition to forward flight is achieved by rotating these nozzles into ahorizontal position. Powered-lift vehicles have certain advantages over conventional strikefighters. Their V/STOL capabilities allow for safer carrier operations, smaller carrier size, andquick reaction time for troop support. Moreover, they are not dependent on vulnerable land-based runways. The AV-8A Harrier first entered service in the British Royal Air Force (RAF)during 1969, and the U.S; Marine Corps (USMC) in 1971. The AV-8B was a redesign toachieve improved payload capacity, range, and accuracy. This modified design first enteredservice with the USMC and RAF in 1985. The success and unique capabilities of the Harder hasprompted the design of a powered-lift version of the Joint Strike Fighter (JSF).The flowfield for the Harrier near the ground during low-speed or hover flight operations isvery complex and time-dependent. A sketch of this flowfield is shown in Fig. 1. Warm air fromthe fan is exhausted from the front nozzles, while a hot air/fuel mixture from the engine isexhausted from the rear nozzles. These jets strike the ground and move out radially forming aground jet-flow. The ambient freestream, due to low-speed forward flight or a headwind duringhover, opposes the jet-flow. This interaction causes the flow to separate and form a groundvortex. The multiple jets also interact with each other near the ground and form an upwash or jetfountain, which strikes the underside of the fuselage. If the aircraft is sufficiently close to theground, the inlet can ingest ground debris and hot gasses from the fountain and ground vortex.This Hot Gas Ingestion (HGI) can cause a sudden loss of thrust (powered lift), and the vehiclemay crash. The high-speed jet flow along the ground can also entrain the ambient flow, resultingin a low pressure region underneath the vehicle. The accompanied loss of lift is referred to as thesuckdown effect. The ground vortex may also be highly unsteady, dramatically changing its sizeand position with time at low frequencies, e.g., 1 Hz. 2"Research Scientist, Associate Fellow AIAA.t Research Scientist, Member AIAA.* Senior Research Scientist.0 Senior Research Scientist, Member AIAA.