A study of free jet impingement. Part 1. Mean properties of free and impinging jets

Abstract

In this, the first part of a two-part experimental study of the behaviour of impinging jets, the mean properties of the flow field are established. Velocity profiles are given for three types of jet flow issuing from a circular convergent nozzle. Measured distributions of surface pressure are given which result when the jets impinge both normally and obliquely at various distances on several surface shapes. The pressure distributions are used to compute the radial velocity gradient at the impingement stagnation point. It is found that for normal impingement this gradient correlates with the free jet centreline velocity and half-radius at the same axial location. A fall-off in the correlated value is noted as the impingement is made oblique. Measurements of the azimuthal distribution of momentum flux in the resulting wall jet are also given. The general behaviour of all three types of jet is found to be similar at locations downstream of any local effects due to the shock waves present in the under-expanded types. A special study of the close-range impingement of an under-expanded jet containing a normal shock disk reveals a region of separated flow surrounding the stagnation point. This condition results in a negative value of the radial velocity gradient at the centreline.

Measurement and RANS modelling of large-scale under-expanded CO[sub 2] releases for CCS applications

“…The parameters of these releases are given in Table 1. Figure 2 depicts predictions of the normalized centreline axial velocity, plotted against experimental data for a highly under-expanded air jet [5]. As expected, the unmodified k-İ model over-predicts the jet mixing, leading to an over-dissipative solution.…”

Experimental measurement and Reynolds-averaged Navier–Stokes modelling of the near-field structure of multi-phase CO2 jet releases

“…Figure 6 demonstrates the effect of these modifications upon the axial centre-line velocity profile predictions of a highly under-expanded air jet, reported by (Donaldson and Snedeker, 1971). The standard k-ε model is clearly too dissipative, leading to an early decay of the compression/decompression cycle.…”

Computational Study of Hydrogen Direct Injection for Internal Combustion Engines

“…The three major flow categories of a gas flow jet issued from a circular nozzle are subsonic, moderately under-expanded jet, and highly under-expanded; see Figure 4 for under-expanded cases [31]. When the critical pressure ratio is reached, which is 1.889 for hydrogen, a very weak normal shock is expected to form at the exit.…”

“…The authors specifically concluded that the resolution that they employed was not adequate to resolve these details. Under-expanded jets have been studied for air and gaseous fuels (primarily natural gas), experimentally [31][32][33][34][35] and by LES [36][37][38][39]. In a recent publication on under-expanded jets, Scarcelli et al [40] validated RANS predictions of a sonic argon jet, injected at a flow rate corresponding to 100 bar nominal injection pressure into atmospheric environment, against experimental data obtained by means of X-ray radiography.…”