Fluorescence Imaging of Underexpanded Jets and Comparison with CFD

Abstract

An experimental study of underexpanded and highly underexpanded axisymmetric nitrogen free jets seeded with 0.5% nitric oxide (NO) and issuing from a sonic orifice was conducted at NASA Langley Research Center. Reynolds numbers based on nozzle exit conditions ranged from 770 to 35,700, and nozzle exit-to-ambient jet pressure ratios ranged from 2 to 35. These flows were non-intrusively visualized with a spatial resolution of approximately 0.14 mm x 0.14 mm x 1 mm thick and a temporal resolution of 1µs using planar laser-induced fluorescence (

Visualization of Flowfield Modification by RCS Jets on a Capsule Entry Vehicle

“…For the case of the tunnel-off flow, Fig. 2(a) exhibits a classic underexpanded jet structure 14 with an axisymmetric barrel shock and a Mach disk at the top right of the image (barely visible in this single-shot image). The flow is observed to be transitioning to turbulent far from the nozzle exit, along both top and bottom shear layers just outside the barrel shock.…”

The Effect of Impingement on Transitional Behavior in Underexpanded Jets

“…Earlier papers reported on the transition to turbulence in free (non-impinging) underexpanded sonic jets 9 ; compared three free, steady laminar, sonic nozzle cases with computational fluid dynamics (CFD) results 15 ; explored the relation between flow structures and impingement surface pressure measurements for steady laminar, impinging, supersonic nozzle cases 16 ; and identified instability modes of transition and the importance of flow structures in contributing to flow unsteadiness for free, supersonic nozzle cases. 10 This paper will concentrate on unsteady, impinging jets for both sonic and supersonic nozzle cases.…”

Identification of Instability Modes of Transition in Underexpanded Jets

“…Re exit was affected by nozzle plenum temperature and was varied by changing the mass flow rates. JPR was defined as the ratio of the calculated static pressure at the nozzle exit, p e , to the ambient pressure in the test section, p a , according to (2), and was varied by changing the test section pressure for a given Reynolds number (and therefore, a fixed p e ). …”

“…1 Three steady, laminar cases were compared with computational fluid dynamics (CFD) in another paper. 2 A third paper focused on steady, laminar, impinging jet flows. 3 A future paper will present results for unsteady jets impinging on a flat plate, in regards to the effect of jet impingement upon the process of transition to turbulence.…”