Increasing Jet Temperature Research Articles

The near-field aerodynamic characteristics of hot high-speed jets

Abstract

Numerical simulation of the influence of environmental and jet parameters on supercritical injection

The establishment of fuel injection model and the research of supercritical injection characteristics are crucial to supercritical state fuel injection technology. We established a numerical model of supercritical fuel injection based on the analysis of supercritical aviation fuel injection. The model was modified and validated by existing experimental data. Subsequently, the model was used to simulate supercritical fuel injection into the supercritical environment. The effects of environmental conditions and injection temperature on the jet length and the expansion angle were studied. The following observations were made: (1) Changes in the supercritical fuel jet length and expansion angle decreased with increasing environmental pressure. (2) As the environmental temperature increased, the supercritical fuel jet length and expansion angle did not obviously change. (3) With the increasing jet temperature, the supercritical jet length increased with the increasing jet temperature, but the jet expansion angle did not show obvious changes. In summary, supercritical fuel injection is significantly affected by environmental pressure.

The Scaling of Broadband Shock-Associated Noise with Increasing Temperature

A physical explanation for the saturation of broadband shock-associated noise (BBSAN) intensity with increasing jet stagnation temperature has eluded investigators. An explanation is proposed for this phenomenon with the use of an acoustic analogy. To isolate the relevant physics, the scaling of BBSAN peak intensity level at the sideline observer location is examined. The equivalent source within the framework of an acoustic analogy for BBSAN is based on local field quantities at shock wave – shear layer interactions. Propagation of sound through the jet shear layer is predicted with an adjoint vector Green's function solver of the linearized Euler equations. The combination of the equivalent source and adjoint vector Green's function allows for correct predictions of the saturation of BBSAN with increasing stagnation pressure and stagnation temperature. The sources and vector Green's function have arguments involving the steady Reynolds-Averaged Navier-Stokes solution of the jet. It is proposed that saturation of BBSAN with increasing jet temperature occurs due to a balance between the amplification of the sound propagation through the shear layer and the source term scaling.

An experimental study of tone-excited heated jets

The objective of this investigation was to obtain detailed experimental data on the effects of upstream acoustic excitation on the mixing of heated jets with the surrounding air. Based on the information gathered in the literature survey, a technical approach was developed to carry out a systematic set of mean flowfield measurements for a broad range of jet operating and acoustic excitation conditions. Most of the results were obtained at Mach numbers of 0.3 and 0.8 and total temperatures of up to 800 K. Some measurements were made also for the fully expanded supersonic jet of Mj = 1.15. The maximum level of excitation was Le equal to or less than 150 dB and a range of excitation frequencies up to fe = 4 kHz was used. The important results derived from this study can be summarized as follows: (1) the sensitivity of heated jets to upstream acoustic excitation varies strongly with the jet operating conditions, (2) the threshold excitation level increases with increasing jet temperature, and (3) the preferred Strouhal number does not change significantly with a change of the jet operating conditions.

Effects of forward velocity on sound radiation from convecting monopole and dipole sources in jet flow

A theoretical model is presented of the effects of forward velocity of an aircraft at arbitrary subsonic speed on sound radiated from convecting monopole and dipole sources embedded in the jet flow. The model leads to the prediction that a low frequency model point-monopole or point-dipole source convected at Mach number M c by a jet flow of Mach number M j issuing from an aircraft with flight Mach number M f radiates a field for which p 2 monopole= p 2 static[1−( c o c f )(M c−M f) cosθ] −4[1−( c o c f )(M j−M f) cosθ] −2, p 2 dipole= p 2 static[1−( c o c f )(M c−M f) cosθ] −4[1−( c o c f )(M j−M f) cosθ] −4 The analysis shows that with increasing forward velocity, there is a steadily increasing amplification over the static case of the sound which is radiated into the forward arc and a large reduction of the sound which is radiated into the rearward arc. The same trend is also shown to result when there is a reduction in the exhaust velocity with, however, a further rise in amplification in the forward quadrant and a drop in attenuation in the aft quadrant. Moreover, it is found that there is a dynamic transmission effect which tends to enhance the sound radiation at all angles by a density ratio pf/pj which increases with increasing jet temperature; however, the forward velocity effects, inasmuch as the amplification or reduction over the static case is concerned, in the fore and aft quadrants for the hot and cold jets are exactly the same. Finally, the theory shows that the forward velocity effects at θ = 90° to the jet axis are virtually absent.

High temperature effects on the radiation impedance of an unflanged duct exit

The results of a series of measurements, of the radiation impedance of an unflanged duct termination with high temperature airflow at very low velocity, are presented. The principal difference between these results and the impedance in the absence of temperature gradients is a progressive increase in radiation resistance with increasing jet temperature.