Mixing of an underexpanded rectangular jet ejector

Abstract

An experimental investigation was carried out on a rectangular ejector (constant area mixing duct) with an underexpanded rectangular jet as the primary flow. From the wall static pressure measurements, the ejector performance was found to show irregular variations with the primary jet pressure. Hot-wire measurements, together with schlieren photographs, showed that better performance was obtained when the flow was well mixed. The well-mixed flow was found when the screech tone Strouhal number was in the 0.11-0.14 range, which agrees with the most unstable Strouhal number of the free underexpanded rectangular jet. By incorporating a phase-locked technique with shlieren flow visualization, we were able to photograph standing waves excited by the screech tones inside the ejector mixing duct. The interactions between the jet flow and the screech tones were studied using this flow visualization technique. Nomenclature= cross-sectional area of primary nozzle = cross-sectional area of mixing duct = (p-P a )/Pa> pressure coefficient = C p at the entrance of the mixing duct = average of six C^ measured = 5.0 mm, nozzle width (short dimension) = discrete tone frequency = 70.0 mm, height of mixing duct = 50.0 mm, nozzle length (long dimension) = surface static pressure = jet total pressure = ambient pressure =Po / Pa> J et pressure ratio =f*D/U e , Strouhal number = mean velocity = jet exit velocity = mixing duct width = Cartesian coordinates

Effect of primary jet geometry on ejector performance: A cold-flow investigation

“…The velocity of the propagating vortex loop which is circular in nature is considerably less (U T x in Table II If the exit nozzle of the shock tube has an area comparable with the inlet of the ejector, it makes more effective usage of the principle operation of the ejector which is to entrain ambient air. The large spreading of the jet leads to better mixing, a statement in agreement with the findings of Hsia et al 23 The entrained air increases the momentum of the flow and hence the impulse created at the ejector exit. Figure 18 shows a selection of the schlieren photographs which express the main components of the flow created at the exit of the ejector.…”

An Integrated Lumped Parameter-CFD approach for off-design ejector performance evaluation

“…The under expanded flow fields concerns the under-expanded primary flow: at the nozzle's exit plane, the primary flow pressure is higher than that of the secondary flow and the so called 'shock train' (a succession of oblique and/or nor-mal shock waves) occurs. When considering the flow fields in a rectangular shape ejector, the interested reader may also refer to the study of Little et al [1], Hsia et al [47] and Koite et al [48].…”

Performance characteristics of an underexpanded multiple jet ejector

“…For this area ratio and for underexpanded conditions, the C Pf values for the multiple jet ejector are lower, indicating a better performance. The irregular behavior of C P[ for a single jet ejector is a result of acoustic interactions inside the duct, the details of which are described by Hsia et al 2 It was also found that, for subsonic conditions, i.e., for R < 1.9, the difference in the data for single and multiple jet ejectors at corresponding conditions are insignifi-J. PROPULSION VOL.…”