Full-field measurements of self-excited oscillations in momentum-dominated helium jets

Abstract

Flow structure of momentum-dominated helium jets discharged vertically into ambient air was investigated using a high-speed rainbow schlieren deflectometry (RSD) apparatus operated at up

Buoyancy effects on flow transition in low-density inertial gas jets

“…Buoyant acceleration of the low-density fluid in localized regions of the jet may trigger the instability causing periodic flow oscillations and eventually, the breakdown to turbulence. This explanation is supported by the recent experiments of Yildirim and Agrawal (2004), who found that the flow oscillation frequency normalized by the buoyancy time scale correlated with the jet Richardson number in inertial low-density jets for Ri<0.1. Furthermore, the transition length normalized by injector inside diameter correlated with the jet Richardson number for a given Re, an observation similar to that of Subbarao and Cantwell (1992) in buoyant jets.…”

“…The flow system comprised of on-board compressed helium gas cylinders, a calibrated mass flow meter, a needle valve to set the flowrate, a solenoid valve to initiate and terminate the flow, and a vertically oriented stainless steel tube to serve as the injector. Yildirim and Agrawal (2004) have provided details of the schlieren apparatus. The color schlieren images are acquired by a high-speed digital camera operated at exposure time of 297-µs and acquisition rate of 1000 images per second, providing spatial resolution of 0.2 mm.…”

“…Furthermore, the transition length normalized by injector inside diameter correlated with the jet Richardson number for a given Re, an observation similar to that of Subbarao and Cantwell (1992) in buoyant jets. Yildirim and Agrawal (2004) utilized different diameter injector tubes to vary the jet Richardson number for a given Re. Besides the limited range of the jet Richardson number achieved, the similarity parameters are not perfectly matched using this approach.…”

Frequency selection in globally unstable round jets

“…1. The experiments of Kyle and Sreenivasan 12 showed only one oscillating state, also axisymmetric, with Strouhal number and density ratio ranges in good agreement with the Stϳ 0.45 mode of Monkewitz et al 1 More recent helium jet experiments 14,15 confirm the results of Kyle and Sreenivasan. 12 The linear spatio-temporal instability analysis of Monkewitz and Sohn 16 revealed that hot axisymmetric jets display a region of absolute instability as the temperature ratio falls below a critical value.…”

Optical Display of Transverse Jet Flow Field Under Supersonic Inflow

“…Color schlieren is one of the schlieren techniques which is paid much attention to. A. K. Agrawal et al [3][4][5][6][7][8] , G. E. Elsinga et al [9] and DLR Aerospace Center [10] are well known of their research on color schlieren technique.…”