Numerical Study on Extent of Hazardous Area for Sonic Jet Release Using Equivalent Leak Diameter

In this study, three-dimensional K - E turbulence numerical simulations were conducted to analyze the extent of hazardous area for the sonic jet leakage of flammable gas. Incompressible fluid flows were simulated based on an inlet boundary condition estimated using the theory of “equivalent leak diameter” to prevent the direct simulation of sonic flows near the leakage hole. Numerical simulations of 20 methane leakage scenarios providing the lower explosive limit contour showed shapes of the hazardous area with a maximum height of approximately 12-14 times larger than the maximum width, owing to convection. The extents of hazardous area determined using computational fluid dynamics (CFD) were approximately 5%-10% lower than the results obtained with 1 m over based on IEC 60079-10-1. For scenarios in which quantitative data were not calculated using IEC 60079-10-1 due to low release rates, CFD provided quantitative data for the extent of hazardous area, showing nonlinear relationships with the pressure and diameter of leak holes.

Effectiveness of multiple jets for a finned large slenderness ratio missile in supersonic crossflows

The reaction control system with multiple lateral jets shows great advantages in agility and maneuverability for supersonic air vehicles. Interactions among sonic jet plumes, X-shape fins, and supersonic crossflow at Mach 4.5 and Reynolds number 3.8 × 107 are numerically studied considering different number of jets for a large slenderness ratio missile with 7 jet exits. Three-dimensional Reynolds-averaged Navier–Stokes equations closed by Spalart–Allmaras turbulence model for the structured grid are validated and solved. The overall force and moment amplification factors of configurations with and without fins are analyzed and compared. Moreover, the force and moment amplification factors on fins and ratio of force and moment on fins are proposed and discussed to measure the jet effectiveness contributed from fins. The number of jet plumes is under consideration for all cases. Results show that the increment of effectiveness decreases as the number of jets increases for the finned configuration. Fins can significantly improve the jet effectiveness with more than 70% force and 50% moment increment, which shows great advantages to the jet effectiveness as well as the overall aerodynamic performance.

Study of Correctly Expanded Sonic Jet with Air Tabs

The present numerical study is to understand the effect of air tabs located at the exit of a convergent nozzle on the spreading and mixing characteristics of correctly expanded sonic primary jet. Air tabs used in this study are two secondary jets issuing from constant diameter tubes located diametrically opposite at the periphery of the primary nozzle exit, normal to the primary jet. Two air tabs of Mach numbers 1.0 to 1.4, in steps of 0.1 are considered in this study. The mixing modification caused by air tabs are analysed by considering the mixing of uncontrolled (free) primary jet as a reference. Substantial enhancement in jet mixing is achieved with Mach 1.4 air tabs, which results in 80 % potential core length reduction. The total pressure profiles taken on the plane (YZ) normal to the primary jet axis, at various locations along the primary jet centreline revealed the modification of the jet cross sectional shape by air tabs. The stream-wise vortices and bifurcation of the primary jet caused by air tabs are found to be the mechanism behind the enhanced jet mixing.

Self-oscillatory flow in the Hartmann resonator – Numerical simulation

Self-oscillatory flow in the Hartmann resonator is numerically calculated within the framework of ideal (inviscid and non-heat-conducting) gasdynamics. The calculations are performed for the case of a sonic jet impinging on a tube varying from that with a sealed inlet (rod) to a fairly deep cavity. The spacing between the tube and the nozzle and the nozzle pressure ratio are also varied in the calculations. On the basis of the calculated results the oscillation process is described in detail and its mechanism is revealed for both shallow and deep tubes. For shallow tubes and a rod it is due to an imbalance in the flow rate and momentum between two regions in the jet that impinges on the obstacle. For deep tubes the oscillations are due to the tube filling and evacuation somewhat reminiscent of the process occurring in a one-quarter-wave resonator. In any case no signature of a feedback loop in the external acoustic field of the jet was detected. The results of the calculations are in good agreement with experimental data. The effects of mounting a lip on the tube (transition from a low- to high-frequency operation mode) and heating in the Hartmann tube are also discussed.