Some observations of the transition process on the windward face of a long yawed cylinder

TLDR

The study investigates how yaw affects transition in the boundary layer on the windward face of a long cylinder. The experiment employed china‑clay‑evaporation, surface‑oil‑flow, hot‑wire anemometry, and surface Pitot tubes to observe stationary and time‑dependent disturbances and to compare transition criteria with Owen & Randall’s model. The boundary layer is susceptible to large‑amplitude time‑dependent disturbances before transition, Owen & Randall’s criteria are inadequate, and the detailed raw data enable future model testing.

Abstract

An experiment has been performed to determine the effect of yaw upon transition in the boundary layer formed on the windward face of a long cylinder. The china-clay-evaporation and surface-oil-flow techniques have been used to study the development of the fixed-wavelength stationary disturbances which are characteristic of cross-flow instability. It has been found that the boundary layer is also susceptible to time-dependent disturbances which grow to very large amplitudes prior to the onset of transition. These disturbances have been studied with a hot-wire anemometer. The conditions necessary for the onset and completion of transition have been determined by the use of surface Pitot tubes. Data from the experiment have been compared with the simple criteria for instability and transition which were proposed by Owen & Randall over thirty years ago. In general it has been found that these criteria are inadequate, and, where possible, improvements have been proposed. The raw data are presented in sufficient detail for them to be used to test, or calibrate, future theoretical models of the transition process in three-dimensional boundary-layer flows.