Atomic Spectra Database

Numerical Investigation of Mixing and Combustion Enhancement in Supersonic Combustors by Strut Induced Streamwise Vorticity

The free-space Green’s function is used to evaluate electromagnetic wave scattering and radiation from currents in free space. This section investigates two examples using the free-space Green’s function, namely, radiation from a sheet current and radiation from a shell current.

Green’s Functions: Applications

Transverse jet in supersonic crossflows

A review on hydrogen industrial aerospace applications

An experimental and computational study of an aerodynamic ramp (aeroramp) injector was conducted at Virginia Polytechnic Institute and State University. The aeroramp consisted of an array of two rows with two columns of flush-wall holes that induce vorticity and enhance mixing. The holes were spaced four diameters apart in the streamwise direction with two diameters transverse spacing between them. For comparison, a single-hole circular injector with the same area angled downstream at 30 deg was also examined. Test conditions involved sonic injection of helium heated to 313 K to safely simulate hydrogen into a Mach 4 air cross stream with average Reynolds number 5.77 e+7 per meter at a jet to freestream momentum flux ratio of 2.1. Sampling probe measurements were utilized to determine the local helium concentration. Pitot and cone-static-pressure probes and a diffuser thermocouple probe were employed to document the flow. This allowed total pressure losses to be determined. The numerical flow solver used was GASP v. 4.2. The inviscid fluxes were computed in three dimensions using third-order AUSM+ with modified essentially nonoscillatory limiting. The AUSM+ algorithm was chosen because of its good resolution of shock discontinuities and its efficiency. The Wilcox k-ω (1998) turbulence model was used. The main results of this work can be summarized as follows: 1) the mixing efficiency value of this aeroramp design, which was optimized at Mach 2.4 for hydrocarbon fuel, was only slightly higher than that of the single-hole injector at these flow conditions; 2) the mass-averaged total pressure loss parameter showed that the aeroramp and single-hole injectors had the same overall losses; 3) the computational fluid dynamics (CFD) was unable to accurately predict the quantitative mixing data produced by the experiment, however, the qualitative comparisons of the injectors using the CFD predictions agreed with the experiment.

Experimental and computational investigation of light-gas injectors in mach 4.0 crossflow

An experimental study of the effects of injectant molecular weight on transverse-jet mixing in a supersonic crossflow is reported. In addition, the effects of an oblique shock impinging near the injection station were investigated. The examined gaseous injector is circular in geometry and angled downstream at 30 deg to the horizontal. Test conditions involved sonic injection of helium, methane, and air at a jet-to-freestream momentum flux ratio of 2.1 into a nominal Mach 4 air cross stream with average Reynolds number 5.77e + 7 per meter to provide a range of injectant molecular weights from 4―29. Sampling probe measurements were used to determine the local helium and methane concentration. A miniature five-hole pressure probe, pitot and cone-static pressure probes, and a diffuser-thermocouple probe were employed to document the flow. The goals of this effort are twofold. The first goal is to broaden and enrich the database for transverse injection in high-speed flows. Second, these data will aid greatly in the development of advanced turbulence models with a wide range of applicability for high-speed mixing flows. The main experimental results showed that an impinging shock reduces penetration and increases mixing for injectants of all molecular weights. Higher molecular weight injectant seems to increase penetration, but the effect is weak. The effects of shock impingement were strongest when this occurred downstream of, and closest to, the injection port.

Molecular Weight and Shock-Wave Effects on Transverse Injection in Supersonic Flow

For air-breathing propulsion systems intended for flight at very high Mach numbers, combustion is carried out at supersonic velocities and the process is mixing limited. Substantial increase in mixing rates can be obtained by fuel injection strategies centered on generating selected modes of supersonic, streamwise vortex interactions. Despite the recognized importance, and potential of the role of streamwise vortices for supersonic mixing enhancement, only few fundamental studies on their dynamics and interactions have been conducted, leaving the field largely unexplored. A reduced order model that allows the dynamics of complex, interacting, supersonic vortical structures to be investigated, is presented in this work. The prediction of the evolution of mutually interacting streamwise vortices represents an enabling element for the initiation of an effective, systematic experimental study of selected cases of interest, and is an important step toward the design of new fuel injection strategies for supersonic combustors. The case presented in this work is centered on a merging process of co-rotating vortices, and the subsequent evolution of a system composed of two counter-rotating vortex pairs. This interaction was studied, initially, with the proposed model, and was chosen for the peculiarity of the resulting morphology of the vorticity field. These results were used to design an experimental investigation with the intent to target the same specific complex flow physics. The experiment revealed the same peculiar features encountered in the simulation.

Vortex dynamics studies in supersonic flow: Merging of co-rotating streamwise vortices

The ignition and combustion characteristics of the hydrogen plume issued from two pylon-type injectors in a Mach 2.4, high-enthalpy airflow are presented. Specifically, the focus of the study is on the effects of the imposed interaction and subsequent dynamics of a system of selected supersonic streamwise vortices on the reacting plume morphology and its evolution. The design phase of the experimental campaign was carried out with a reduced-order model, with the goal of identifying peculiar interactions among streamwise vortical structures introduced in the flow of interest. Two vortex interaction modes have been selected and later implemented using ramp-type vortex generators positioned symmetrically and asymmetrically on the pylon injectors, as prescribed by the results of the simulations reported here. Hydrogen/air combustion experiments, aimed at investigating the selected cases, were conducted in the expansion tube facility of the High-Temperature Gas Dynamics Laboratory at Stanford University. Stagn...

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Supersonic combustion of pylon-injected hydrogen in high-enthalpy flow with imposed vortex dynamics

This paper presents the results of experimental and numerical studies of an array of injectors combining inclined circular and diamond-shaped sonic nozzles for application to high-Mach-number airbreathing vehicles with light-gas fuels. The freestream Mach number was 4, and helium was used as the injectant to safely simulate hydrogen fuel. The diamond injector provided improvements in penetration of more than a factor of 2, compared with the circular injectors. This is a greater increase than had been inferred earlier by comparing test results with isolated diamond and circular injectors. The rate of mixing as indicated by the decay of maximum concentration in the plume was about the same. Computational fluid dynamics with a Reynolds-averaged Navier-Stokes formulation was applied to this flow problem with four different turbulence models. The helium-mixing predictions from the four turbulence models showed that the simulations are heavily impacted by the turbulence model selection. None of the turbulence models were able to accurately simulate the helium mixing shown in the experiment, but some models did much better than others. From the selected models, the Wilcox k-w model had the best correlation with the experimental helium-concentration profiles. The computational fluid dynamic solutions were also probed to elucidate the behavior of the flow in the plumes from the circular and diamond injectors. From a design point of view, these results show that it is useful to combine inclined diamond and circular injectors to achieve good fuel coverage and fuel/air mixing across a combustor.

Luca Maddalena

Papers

Experimental and computational investigation of light-gas injectors in mach 4.0 crossflow

Molecular Weight and Shock-Wave Effects on Transverse Injection in Supersonic Flow

Vortex dynamics studies in supersonic flow: Merging of co-rotating streamwise vortices

Supersonic combustion of pylon-injected hydrogen in high-enthalpy flow with imposed vortex dynamics

Complex Wall Injector Array for High-Speed Combustors