Notes on Initial Disturbance Fields for the Transition Problem

The transition process is a 6-stage affair which is initiated by the ambient disturbance environment. These initial disturbance fields, which can be either stream- or body-generated (or a combination thereof) are processed by the body inviscid and viscous flow fields. The resulting disturbances then constitute the initial and bounding values for the subsequent linear and nonlinear growth processes which result, ultimately, in final breakdown to turbulence, e.g., the location of transition per se. The existing state of the art in transition estimation, the e N method (e.g., Reference 1), deals only with the amplification ratio as given by linear theory and hence can only estimate (generally to better than 0(20 percent) currently) transition location when the initial disturbance fields are the equivalent of a “dull hum,” i.e., 0(.05 percent), as they appear to be in quiet, low- disturbance wind tunnels and many atmospheric flight situations. Improved prediction accuracy and/or predictions for non-canonical disturbance fields requires solution of transition as an initial-boundary value problem (via numerical simulations) and specification, for instance in flight, of the amplitude, spectra, orientation, and mode of all initial disturbance fields as a function of latitude, longitude, altitude, and time along the flight path.