The results of an experimental study of the stability of boundary layer free convection from an inclined plane surface are presented. In particular, the relative contributions of hydrodynamic and thermal effects are investigated. It is demonstrated that thermal effects, through surface inclinations, are increasingly significant as the surface departs further from the verticM position and that positive and negative inclinations do not produce equal and opposite effects.
The instability phenomenon was observed with a schlieren apparatus and found to be wave-like. The corresponding characteristics of wavelength, frequency etc., were measured at selected inclinations using thermocouple probes. The effect of inclination on these characteristics is shown to be moderate. The variation in the stability limit of the neutral stability curves is also calculated. ยง 1. Introduction
The stability of a fluid adjacent to a heated surface has been a subject of study for many years, the earliest known work dating back to the later nineteenth century when Thomson Eli and later Bgnard E2~ discovered the onset of cellular convection above a heated horizontal surface. The problem of "a layer of fluid heated from beneath" has since received a great deal of attention, see e.g. references [3, 4, 5, 51. When the heated surface is vertical the problem takes a different form. The transition to turbulence in a moving vertical fluid layer is considered to result from hydrodynamic instability, in distinction *) At present in the Faculty of Engineering,