Aerodynamic characteristics of lambda wings

The results of wind tunnel tests carried out on a semi-span `lambda' planform model with leading and trailing edges swept at 40° are presented. The planform investigated has been specified as having features likely to be encountered on future `ow observable' aircraft. Balance data has been acquired to angles of attack beyond stall for both forward and reverse flow orientations. Dynamic calibration of surface pressure tappings has allowed both time-averaged and unsteady pressures to be measured over the entire upper surface of the wing. Unsteady pressure time histories have been analyzed in the frequency domain to identify their spatial resolution, dominant frequencies and associated magnitudes. In forward flow conditions, maximum buffet is observed between the primary attachment of the leading edge vortex system and the vortex core. The dominant buffet frequency is shown to be dependant on the chordwise location, incidence and free stream velocity as expected. A second coherent buffet frequency has been identified in the region of high buffet over a wide range of operating conditions. Inboard of this region a third dominant frequency has been observed. This is of an intermediate frequency and varies in a similar manner. A simple mechanism has been proposed to explain both the spanwise RMS distribution and the presence of a number of coherent buffet frequencies.