High-temperature Supersonic Jet Research Articles

A standardized approach to identify nonlinearity in fighter jet noise during ground run-ups

High-intensity military sources (explosions, gunfire, fighter jet noise. . . ) fall out of the scope of linearity-based commercial software and international standards. On top of its intrinsic complexity (high temperature supersonic jet, shocks, turbulent eddies, etc), fighter jet engine noise bears additional challenges: turbulent surrounding flow, airframe interference, directionality and tonal components typical of rotating equipment. The absence of a suitable metric to determine the boundary of the nonlinear propagation region can lead to costly mispredictions in the exposure levels for noise abatement procedures and the personnel's safety. The derivative skewness of the time domain signal used as an indicator of spectral reshaping proved effective in setting a threshold to the generation of acoustic nonlinearity for seven firearms. Its application to aircraft noise is here discussed, in order to verify the claim of persistence of nonlinear behaviour at large distances and set the foundations for a common framework contemplating the peculiarities of each military noise source. The experimental data was collected during a series of static ground run-ups of an F-16 military jet aircraft. The results from five engine regimes and two propagation paths are compared with the findings from firearms, existing literature and the solution of a nonlinear acoustic propagation solver.

Proračun sile trenja i toplotnog uticaja mlaza mlaznog motora na unutrašnju površinu lansirne cevi

Introduction/purpose: To study the dynamics of launchers with sources of high-energy gas jets, it is relevant to calculate shear forces from the action of a high-temperature supersonic jet on the inner surface of a cylindrical channel and the temperature of the channel walls. The aim of this work is to develop a comprehensive method for calculating aerodynamic friction and heating on the inner surface of a tubular guide of a rocket. Methods/results: The research method is based on the theory of supersonic gas flows in cylindrical channels and the theory of the boundary layer. The gas jet is considered continuous, stationary and axisymmetric. The system of differential equations of motion of the projectile in the guide integrates numerically over time. The flow parameters in the pipe sections are found according to the dependences of the theory of supersonic gas flows, taking into account friction losses. To calculate shear stress on the guide wall, we use the relations of the asymptotic theory of the turbulent boundary layer, the theory of turbulent spots of Emmons of the transition boundary layer, and data on the Reynolds numbers of the beginning of the laminar-turbulent transition in wind tunnels. At the same time, the differential equation for heating the thin wall of the guide in the range of contact between the surface of the guide and the jet is numerically integrated. The calculations of the distribution of flow parameters, friction force and the temperature of the wall of the tubular guide during the movement of the projectile inside the jet from the moment the engine is started to the moment the shell exits completely from the guide are performed and graphically presented. Conclusions: This method of calculating aerodynamic friction and heating on the inner surface of a tubular guide of a rocket due to a high temperature supersonic gas jet - taking into account the effects of nonisothermality, compressibility and laminar-turbulent transition in the boundary layer - can be used to study the dynamics of the launch of rockets from launchers equipped with tubular guides.

Cooling Effect of Water Injection on a High-Temperature Supersonic Jet

The high temperature and high pressure supersonic jet is one of the key problems in the design of solid rocket motors. To reduce the jet temperature and noise, cooling water is typically injected into the exhaust plume. Numerical simulations for the gas-liquid multiphase flow field with mixture multiphase model were developed and a series of experiments were carried out. By introducing the energy source terms caused by the vaporization of liquid water into the energy equation, a coupling solution was developed to calculate the multiphase flow field. The temperature data predictions agreed well with the experimental results. When water was injected into the plume, the high temperature core region area was reduced, and the temperature on the head face was much lower than that without water. The relationship between the reduction of temperature on the bottom plate and the momentum ratio is developed, which can be used to predict the cooling effect of water injection in many cases.

On the Scaling Laws and Similarity Spectra for Jet Noise in Subsonic and Supersonic Flow

The scaling laws for the simulation of noise from subsonic and ideally expanded supersonic jets are reviewed with regard to their applicability to deduce full-scale conditions from small-scale model testing. Important parameters of scale model testing for the simulation of jet noise are identified, and the methods of estimating full- scale noise levels from simulated scale model data are addressed. The limitations of cold-jet data in estimating high-temperature supersonic jet noise levels are discussed. New results are presented showing the dependence of overall sound power level on the jet temperature ratio at various jet Mach numbers. A generalized similarity spectrum is also proposed, which accounts for convective Mach number and angle to the jet axis.

Molecular Resonances Observed in the Predissociation of Cs2

Very cold molecular beam of Cs2 is generated by a high temperature supersonic jet source. State-specific photofragment yield spectrum is obtained in the orange band of Cs2. Asymmetric line shapes are observed. The Fano line shape parameter, q, shows a gradual sign change, which is called “q-reversal”. A very broad absorption band which has about 50 cm-1 width is observed and explained to occur through the perturbation by the D1∑u+ state. The complex resonance line shapes are attributed to the interfering resonances.

Mach wave emission from a high-temperature supersonic jet

The paper considers the compressible Rayleigh equation as a model for the Mach wave emission mechanism associated with high temperature supersonic jets. Solutions to the compressible Rayleigh equation reveal the existence of several families of supersonically convecting instability waves. These waves directly radiate noise to the jet far field. The predicted noise characteristics are compared to previously acquired experimental data for an axisymmetric Mach 2 fully pressure balanced jet operating over a range of jet operating total temperatures from ambient to 1370 K. The results of this comparison show that the first order supersonic instability wave and the Kelvin-Helmholtz first, second, and third order modes have directional radiation characteristics that are in agreement with observed data. The assumption of equal initial amplitudes for all of the waves leads to the conclusion that the flapping mode of instability dominates the noise radiation process of supersonic jets. At a jet temperature of 1370 K, supersonic instability waves are predicted to dominate the noise radiated at high frequency at narrow angles to the jet axis.

Some Results of Experiments Relating to the Generation of Noise in Jets

Some sample experimental results relating to the nature and sources of noise in jets are presented. Previous work is extended to include more detailed information about the jet structure. In this regard noise data are compared for jets having somewhat different turbulence profiles. High temperature jets are noted to have different radiation patterns and to be more efficient noise radiators than low temperature jets. Noise data for the high temperature supersonic jet of a rocket engine are included for comparison with those of subsonic jets. Some experiments have shown the noise levels at the low frequencies can be markedly reduced by the use of grids in the jet stream.