An experimental investigation of disturbance amplification in external laminar natural convection flow

Abstract

An experimental investigation has been carried out on the nature of disturbance amplification in the laminar natural convection boundary layer formed on a vertical flat surface with uniform heat flux input. A pair of calibrated hot-wire anemometers were used to obtain amplitude and phase profiles of disturbance velocities and to measure the distance amplification rate as a function of disturbance frequency. An interferometer was used to measure the amplitude and phase profiles of disturbances in the temperature field. The relative amplification of a temperature disturbance was measured as it was convected downstream. For this latter measurement a technique employing interferometric moiré patterns was used. All of these measurements are in good agreement with the theory. The results of this investigation further strengthen the conclusions drawn in an earlier theoretical investigation, that the frequencies which amplify fastest and lead to transition and turbulence occupy a band much higher than the frequencies which begin to amplify first. These results also support stability theory in the very close agreement between calculated and measured distributions of disturbance quantities.