High-speed rainbow schlieren visualization of an oscillating helium jet undergoing gravitational change

Abstract

Rainbow schlieren deflectometry combined with high-speed digital imaging was used to study buoyancy effects on flow structure of a helium jet discharged vertically into air. The experimental data were taken using the 2.2-sec drop tower facility at the NASA John H. Glenn Research Center in Cleveland, Ohio. The test conditions pertained to jet Reynolds number of 490 and jet Richardson number of 0.11, for which buoyancy is often considered unimportant. Experimental results show global oscillations at a frequency of 27 Hz in Earth gravity. In microgravity, the jet oscillations vanished and the jet width increased. Results provide a direct physical evidence of the importance of buoyancy on the flow structure of lowdensity gas jets at a Richardson number considered too small to account for gravity.

Influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium plasma jets

“…As analyzed earlier, the plasma propagation is determined by the helium distribution which strongly depends on the helium jet flow pattern at a constant of applied voltage pulse. From earlier investigation on helium jet [30][31][32] , the helium jet flow pattern can be determined by relevant dimensionless numbers, which are the jet Reynolds number (Re) and Richardson number (Ri), defined as follows:…”

“…However, when the momentum is dominated in the helium jet at Ri of the order of 10 -3 , the buoyancy is considered negligible [31][32][33] The Re-l curve is in good approximation independent on the jet diameters. Therefore, the relationship between V and L can be calculated for other jet diameters from one L-V curve at a given discharge pulse.…”

Oscillation and collective behavior in convective flows

“…Since the flow of Helium in air does not emit visible light, the experimental methods used for candle flames [9] had to be modified. The Schlieren technique [12,13] proved to be a simple and efficient method to visualize the flow in rising Helium columns.…”

Computational fluid dynamics approach for understanding oscillating and interacting convective flows

“…For validating the numerical results, the present work considers as reference the experiments realized using a controlled flow of Helium into air 1 . In these experiments the Schlieren technique 12,13 was used to visualize the flow, allowing also a digital processing of the oscillations.…”