posted on 2021-04-13, 13:12authored byJim McGuirk, T Feng
Motivated by design challenges related to aerospace propulsive jets, an experimental
investigation has been conducted of the high Mach number jet plume flow field from
a round convergent nozzle at under-expanded shock-containing conditions. Hot jets up
to a total temperature ratio of 3 were considered. Laser doppler anemometry (LDA)
measurements in the jet near field (first 15 nozzle exit diameters) captured the turbulent
mixing process in detail, enabling the separate effects of compressibility and static
temperature ratio (t) on the development of the velocity and turbulence profiles to be
identified. Compressibility dominated in the initial shear layer region, whereas temperature
effects controlled the downstream jet merging zone. Analysis of shear layer development
demonstrated that, at all temperature ratios, a similar, but significantly stronger, damping
effect was observed as in planar shear layers (correlated well by convective Mach number
Mc). Consideration of the interaction of compressibility and temperature ratio – which
reduce/enhance turbulent mixing respectively – provided for the first time a rational
explanation of the observation that increasing jet temperature influenced flow development
only up to a static temperature ratio t ∼ 1.5, after which further increase has little effect.
Measurements of the potential core length (Lp) were analysed to produce an empirical
correlation that also illustrated the diminishing effects of heat addition at all jet Mach
numbers. The data provide the improved understanding and empirical design techniques
essential for developing technologies for jet noise and infra red (IR) signature reduction
and represent an important validation test case for computational fluid dynamics (CFD)
modelling.
Funding
EPSRC (Grant No GR/S27467/01)
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
This is an Open Access Article. It is published by CUP under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/