Joseph A. Schetz

Comparison of Physical and Aerodynamic Ramps as Fuel Injectors in Supersonic Flow

An experimental investigation was conducted to compare the supersonic mixing performance of a novel e ush-wall aerodynamic ramp injector with that of a physical ramp injector. The aerodynamic ramp injector consists of nine e ush-wall jets arranged to produce fuel‐ vortex interactions for mixing enhancement in a supersonic crosse ow. Test conditions included a Mach 2.0 crosse ow of air with a Reynolds number of 3.63 10 7 per meter and helium injection with jet-to-freestream momentum e ux ratios of 1.0 and 2.0. Conventional probing techniques, including species composition sampling, were employed to interrogate the e owe eld at several downstream locations. Results show that with increasing jet momentum the aeroramp exhibited a signie cant increase in fuel penetration, whereas the physical ramp showed no discernible change. The near-e eld mixing of the aeroramp was superior to that of the physical ramp; however, the physical ramp reaches a fully mixed condition at approximately half the distance of the aeroramp. As the jet momentum was increased, the far-e eld mixing performance of the aeroramp approached that of the physical ramp. In all cases the total pressure loss incurred with the aeroramp was less than that caused by the physical ramp. For both injectors the total pressure loss decreased with increasing jet momentum. It was concluded that, although physical ramps may provide better far-e eld mixing, properly designed e ush-wall injection can provide comparable mixing performance while avoiding the practical problems associated with an intrusive geometry in a scramjet combustor.

Detailed flow physics of the supersonic jet interaction flow field

The jet interaction flow field is the name given to the fluid dynamics phenomenon produced by a jet exhausting in a cross flow. This flow field can be found in several technological applications and, due to the presence of separated flows, vortical motions, turbulence, and, if the flow is supersonic shocks and expansion fans, is a formidable fluid dynamics problem. The AGARD conference proceedings 1 give an ample and detailed review of the range of possible applications. Examples range from the low-speed regimes of a chimney plume in a cross flow to the very high-speed regimes of scramjet combustion and missile control systems, from the low mass flow cases of boundary layer control systems and gas-turbine blade cooling to the high mass flow cases of a landing V/STOL vehicle. The basic problem of a fluid injected into a cross flow has several variables depending on its intended application: injector yaw and pitch angle, jet flow conditions subsonic, sonic, and supersonic, freestream conditions subsonic, supersonic, laminar, and turbulent, not to mention the phase and the chemical composition of the injectant single or multiphase, nonreacting or reacting mixture, etc..

Normal, Sonic Helium Injection Through a Wedge-Shaped Orifice into Supersonic Flow

Helium was injected normally to a Mach 3 airstream to simulate hydrogen fuel injection in a scramjet combustor. Two geometries were evaluated, a wedge-shaped wall orie ce and a circular wall orie ce. Injection was sonic in both geometries, and the expansion ratios and mass e ow rates were matched to isolate the effects of the geometric difference. Surface oil e ow patterns were inspected to determine the extent of boundary-layer separation upstream of each injector, shadowgraphs were used to visualize the e owe elds, and probe measurements were utilized to determine local helium concentrations. The wedgeshaped injection scheme demonstrated more rapid penetration into the freestream and increased mixing when compared to the baseline circular orie ce. In addition, the oil e ow photography showed that the wedge-shaped injector had no upstream separation zone, whereas the circular injector had a large separation zone. The wedge cone guration would therefore be expected to exhibit reduced wall heat transfer in an actual combustor. It is concluded that wedge-shaped, normal, fuel injectors should provide generally better performance than circular normal injectors in supersonic combustors.

Sonic injection from diamond-shaped orifices into a supersonic crossflow

The plume from a diamond-shaped, sonic injector orifice was studied experimentally in a Mach 3 crossflow. The structure of the plume, as well as the near injector flowfield, were examined by flow visualization techniques,and penetration height growth and maximum concentration decay were evaluated from aerothermodynamic probing measurements at two downstream stations. For the transverse injection, the jet-to-freestream dynamic pressure ratio was varied from 0.3 to 2.0. At lower dynamic pressure ratios, the plume from the diamond-shaped injector penetrated farther across the main flow compared to that from an equivalent circular injector, whereas an increase in the dynamic pressure ratio resulted in a deterioration of the plumes sharpness, and penetration of the plume became comparable to that from the circular injector. Angled injections were applied to the diamond-shaped orifice to enhance the penetration at a high dynamic pressure ratio of 2.0. Giving sweepback angle to the orifice was as effective as the case with circular injectors in enhancing the penetration. Adding a moderate yaw angle to the sweptback, diamond-shaped orifice resulted in greatly enhanced penetration, unlike the case with the circular injector. In all cases, the decay rate of the maximum concentration was almost insensitive to the orifice shape.

Improved Aerodynamic-Ramp Injector in Supersonic Flow

An experimental study was performed in the Virginia Polytechnic Institute and State University supersonic wind tunnel on a simplified and revised multiport aerodynamic-ramp injector array in a supersonic flow. The new aerodynamic-ramp injector consisted of four flush-walled holes, in contrast to the original nine-hole versions. For comparison, a single, low downstream-angled circular injector hole was examined. Test conditions included sonic air injection into a Mach 2.4 air cross stream with an average Reynolds number of 4.2 x 10 7 /m at jet-to-freestream momentum flux ratios from 1.1 to 3.3. Shadowgraphs and surface oil-flow visualization pictures were taken in the vicinity of the injectors to gain a qualitative assessment of the injector flowfields. Quantitative measurements of the pressure field on the surface near injectors and in a cross-stream plane downstream were conducted using pressure-sensitive paint and pitot/cone-static probes, respectively. The mixing characteristics of the injectors at three downstream stations were quantified using total temperature probes and a combination of heated and unheated injected air profiles to generate a mixing analog to concentration. Results showed that the aerodynamic-ramp mixed faster and had a larger plume area than the single-hole injector, while sustaining somewhat higher pressure losses due to increased blockage and a higher downstream-angled injector arrangement.

Mixing of Transverse Jets and Wall Jets in Supersonic Flow

A critical review of the available high speed mixing experimental database is presented. Experiments of concern involve measurements of species concentration downstream of sonic or supersonic injection of a light gas into a supersonic air stream. Several classes of injection are considered including transverse jets, wall slots, and some hybrid cases. The review is made difficult by the sparseness of the current database. Mixing data is summarized primarily in the form of the downstream decay of the maximum concentration. Most of the data in the far field can be fitted to a. power law curve with the exponent giving an indication of the rate of mixing. The resulting plot of the experiments presented provides a basis for preliminary comparison of high speed injection concepts. Spacing of jets below a critical value can reduce the rate of mixing by a factor ot two. Initial mixing for transverse jets is strongly dependent on the dynamic pressure ratio. The farfield mixing rate for wall slot injectors is found to be comparable to that for arrays of transverse jets, not slow as has been believed. As a crude estimate, it is shown that all the data for all the configurations falls into a band with a decay rate of about.T0,8. The need for more high quality experiments for high speed mixing in support of such difficult problems as supersonic combustion is apparent. The need for careful sampling probe design is emphasized. Finally, the state of analyses for these flows is discussed. A new analysis for arrays of transverse jets is presented.

Conceptual Design Studies of a Strut-Braced Wing Transonic Transport

Recent transonic airliner designs have generally converged upon a common cantilever low-wing configuration. It is unlikely that further large strides in performance are possible without a significant departure from the present design paradigm. One such alternative configuration is the strut-braced wing (SBW), which uses a strut for wing-bending load alleviation, allowing increased aspect ratio and reduced wing thickness to increase the lift to drag ratio. The thinner wing has less transonic wave drag, permitting the wing to unsweep for increased areas of natural laminar flow and further structural weight savings. High aerodynamic efficiency translates into smaller, quieter, less expensive engines and less pollution. A multidisciplinary design optimization (MDO) approach is essential to realize the full potential of this synergistic configuration caused by the strong interdependence of structures, aerodynamics, and propulsion. NASA defined a need for a 325-passenger transport capable of flying 7500 n miles at Mach 0.85 for a 2010 service entry date

Full Configuration Drag Estimation

Accurate drag estimation is critical in making computational design studies. Drag may be estimated thousands of times during a multidisciplinary design optimization, and computational fluid dynamics is not yet possible in these studies. The current model has been developed as part of an air-vehicle conceptual-design multidisciplinary design optimization framework. Its use for subsonic and transonic aircraft configurations is presented and validated. We present our parametric geometry definition, followed by the drag model description. The drag model includes induced, friction, wave, and interference drag. The model is compared with subsonic and transonic isolated wings, and a wing/body configuration used previously in drag prediction workshops. The agreement between the predictions of the drag model and test data is good, but lessens at high lift coefficients and high transonic Mach numbers. In some cases the accuracy of this drag estimation method exceeds much more elaborate analyses.

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

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.

Design Optimization of a Truss-Braced-Wing Transonic Transport Aircraft

the conventional cantilever configuration. One comparison produces a reduction of 45% in the fuel consumption while decreasing the minimum takeoff gross weight by 15%. For a second comparison, the fuel weight is reduced by 33% with a decreased minimum takeoff gross weight of 19%. Very attractive vehicle performance can be achieved without the necessity of decreasing cruise Mach number. The results also indicate that a truss-braced wing has a greater potential for improved aerodynamic performance than other innovative aircraft configurations. Further studieswillconsidertheinclusionofmorecomplextrusstopologiesandotherinnovativetechnologiesthatarejudged to be synergistic with truss-braced-wing configurations.