Transition Over C4 Leading Edge and Measurement of Intermittency Factor Using PDF of Hot-Wire Signal

Abstract

The variation of intermittency factors in the transition region of a C4 leading edge flat plate is measured at three incidence angles in a low-turbulence free stream. During the determination of intermittency factor, the threshold value of the detector function and the validity of conditional averaging are verified by a method based on the direct application of PDF of the hot-wire output. As the angle of incidence is increased, the transition progressively moves through all the three modes on the suction surface: at zero incidence the bypass transition, at 2 deg incidence the natural transition, and at 4 deg incidence the separated-flow transition occur, respectively. All three modes of transition exhibited the chordwise intermittency factor variation in accordance with Narasimha’s universal intermittency distribution; thus, the method based on spot production rate is applicable to all the three modes of transition. In the transition zone of the attached boundary layers, the conditionally averaged interturbulent profiles are fuller than the Blasius profile, while the conditionally averaged turbulent profiles follow a logarithmic profile with a variable additive parameter.