Use of heated grooves for reduction in friction resistance

Abstract

An analysis of the use of heated grooves for resistance reduction was carried out. The model problem consisted of two parallel plates in a relative motion. The stationary plate was equipped with grooves characterized by a sinusoidal pattern and exposed to a pattern of sinusoidal heating. The force required to maintain plate movement was used to judge changes in flow resistance. It was shown that isothermal grooves increase resistance, periodic heating of smooth plate reduces resistance, while periodic heating of grooved plate may either increase or decrease this resistance. The net effect depends on the relative position of the groove and heating patterns, which controls the strength and direction of the pattern interaction effect, and correct selection of this position may eliminate a significant portion of resistance. Increasing groove amplitude and heating intensity reduces resistance similarly to reducing the Prandtl number. The formation of separation bubbles is essential to resistance reduction; an increase in the plate velocity washes these bubbles away, thus eliminating the resistance-reducing effect.