Russell R. Boyce

The HyShot Scramjet Flight Experiment - Flight Data and CFD Calculations Compared

An analysis has been made using CFD of selected points on the HyShot scramjet flight experiment trajectory. Two-dimensional intake calculations have been done to assess the influence of angle of attack on the performance of the intake and cowl shock/boundary layer bleed duct, and have shown that at low angles of attack the configuration is well behaved, but at high angles of attack the cowl shock separates the boundary layer on the main intake ramp. This sends a separation shock into the combustion chamber. For selected altitudes during the flight for which the maximum angle of attack is a local minimum and for which there is zero yaw, intake and combustor calculations have been made. The calculations consistently predict that supersonic combustion has been obtained. At higher altituudes, reasonable agreement between the measured and predicted pressures is found, although the fuel-off pressures are underpredicted by approximately 15%. At lower altitude, further into the experiment, the flight data is well underpredicted. Further investigations of the flight data are required to assess this, including the possibility of leading edge ablation and/or intake distortion due to the high flight heat loads.

Radical farm ignition processes in two-dimensional supersonic combustion

A two-dimensional numerical study was performed of the ignition processes associated with the concept of radical farming for supersonic combustion. In a preliminary parametric study, a range of freestream conditions attainable in a hypersonic shock tunnel was investigated and mapped according to whether or not the behavior known as radical farming is present: a combustion-induced pressure rise in second or subsequent hot pockets rather than the first Two such cases were analyzed in detail, both having mean conditions across the combustion-chamber entrance that would result in extremely long ignition lengths. The initiation, branching cycle, and heat release reactions in the combustion process become active in the radical farm, and H and OH radicals are produced. Their rate of production slows in the regions of flow expansion, but does not approach chemical freezing until toward the end of the localized expansion zones. Simultaneously, heat release elevates the local temperature. When the mixture flows through the shock at the second hot pocket, the elevated temperature and the presence of radicals enable the branching cycle and three-body recombination heat release reactions to accelerate, and significant pressure rise due to heat release is then able to occur. The extent to which this is completed in the second hot pocket depends on the inflow conditions.

Numerical investigation of transverse jets through multiport injector arrays in supersonic crossflow

A three-dimensional numerical study has been performed of the effects of sonic gaseous hydrogen injection through multiple transverse injectors subjected to a supersonic crossflow. Solutions were obtained for a series of injection configurations in a Mach 4.0 crossflow, with a global equivalence ratio of o = 0:5. Results indicate a different flow structure than for a typical single jet, with the development of two clearly defined wake vortices, including a stagnation point and reversed flow region immediately behind each downstream jet. While the overall penetration was reduced under the investigated conditions, significant improvements were observed when nondimensionalizing against the equivalent jet diameter for each modeled injector row. This was found to be the result of increased jet-to-freestream momentum ratio due to the subsonic flow regions between each injector. Further enhancements were also observed in terms of mixing performance for the multijet cases. Improvements of up to 5% in the overall mixing efficiency were experienced by using multiple jets due to increased mixant interface area and intermediate stirring through wake vortices between each injector. No improvement in far-field mixing was observed. Overall, it has been demonstrated that there are benefits to be gained through the injection of gaseous hydrogen from many small injectors rather than fewer large injectors. Copyright

Comparison of Supersonic Combustion Between Impulse and Vitiation-Heated Facilities

A comparison has been made between supersonic combustion in two commonly used, but fundamentally different, facilities for scramjet research, a vitiation-heated blowdown tunnel and a free-piston shock tunnel. By passing the shock-tunnel freestream flow through a normal shock and then expanding it to Mach 2.5, combustor inlet conditions and geometries were nominally replicated between the two facilities. A constant-area rectangular duct and a diverging duct, both employing central-strut hydrogen injection, were used. Boundary-layer separation and choking in the constant-area duct limited supersonic combustion comparisons up to a fuel equivalence ratio of the order of 0.3. The experimental results also show that the onset of boundary-layer separation occurs at the same combustor pressure loads and that it behaves similarly in the different facilities. With the diverging duct, comparisons were made up to an equivalence ratio of 1.05. Agreement between the results obtained in the two facilities is within experimental error when the different freestream and boundary layers are accounted for.

Inlet Starting of High-Contraction Axisymmetric Scramjets

Reliable in-flight starting of the inlet is of critical importance for the successful operation of scramjet engines, particularly axisymmetric configurations with high-contraction inlets. The present research is undertaken to examine the capability of various inlet starting methods based on two principles: unsteady flow effects and variable geometries. Time-accurate viscous computations have been performed to investigate the transitional flowfields introduced by a variety of methods that are applicable to axisymmetric geometries. Parametric studies have been conducted for instantaneous rupture of conical diaphragms and addition of bleed slots, which induce highly unsteady flow phenomena. Several methods employing variable inlet geometries have been tested for the latter principle, including opening doors and sliding doors (or diaphragm erosion). Successful inlet starting has been achieved as a result of unsteady transition induced by diaphragm rupture and quasi-steady transition, due to the sliding-door opening process. In particular, a bleed addition to the diaphragm rupture method has been found to be highly effective and pronounced flow stability has been observed in the sliding-door process.

OH PLIF Imaging of Supersonic Combustion using Cavity Injection

Planar laser-induced fluorescence of the hydroxyl radical is used to investigate a cavitybased fuel injection system for scramjet operation at a flight Mach number of 11.5. Hydrogen and ethylene fuels are compared over a range of fuel-lean global equivalence ratios. Both fuels show evidence of combustion at each fuel injection pressure. Hydrogen burns diffusively in the shear layer and further downstream, with penetration distance increasing linearly with injection pressure. The combustion in the cavity shear layer sheds regular vortices. Ethylene behaves similarly to hydrogen at the lower equivalence ratios but shows evidence of intense, localized combustion at the highest equivalence ratio. In all cases combustion occurs in the shear layer above the cavity rather than in the recirculating cavity flow.

Scramspace: Scramjet-based access-to-space systems

Scramjet-based launch systems offer considerable promise for safe, reliable and economical access to space. Through both flight and ground tests, leveraging Australias world leadership in scramjet R and D, the SCRAMSPACE project will answer key scientific and technological questions and build an industry-ready talent pool for a future Australian scramjet-based access-to-space industry.

Physical insight into scramjet inlet behavior via multi-objective design optimization

Scramjet propulsion is a promising technology for reliable and economical access to space and high-speed atmospheric transport. The inlet plays a key role in determining the performance of scramjets, in particular for the axisymmetric class of scramjet engines that are currently explored due to their advantages in numerous aspects. In the present study a multi-objective design optimisation (MDO) has been conducted with respect to four major inlet design criteria: compression efficiency, drag, adverse pressure gradient, and exit temperature. The former three criteria are used as the objective functions and the last as the constraint function to evaluate the inlet flowfields in the state-of-the-art coupled CFD / MDO approach. The influential parameters and key physics have been identified by scrutinising the flowfields that have been obtained as an outcome of the optimisation.

Simulations of mixing in an inlet-fueled axisymmetric scramjet

An unsteady simulation of a simple axisymmetric inlet-fueled scramjet engine concept is performed using a hybrid Reynolds-averaged Navier–Stokes and large-eddy simulation approach. The freestream has a Mach number of 7.5 with Mach 8 flight enthalpy. The simulation is of a nonreacting case in which hydrogen is injected into nitrogen. The simulation is used to provide a detailed description of the structure of the flow. The simulation shows that a large-scale pair of counter-rotating vortices forms within the scramjet combustor, with rotation opposite to the rotation of the pair that forms further upstream due to the interaction of the fuel plume with the crossflow. This vortex pair is found to significantly alter the shape of the hydrogen fuel plume and increase the rate at which the hydrogen is mixing by more than a factor of 2 compared to before the vortex pair is formed. The distribution of hydrogen is examined in detail. The time-averaged and fluctuating wall pressures, the mean velocity field, and res...

Nozzle Design Optimization for Axisymmetric Scramjets by Using Surrogate-Assisted Evolutionary Algorithms

Scramjet propulsion is a promising hypersonic airbreathing technology that offers the potential for efficient and flexible access to space and high-speed atmospheric transport. Robust nozzle design over a range of operating conditions is of critical importance for successful scramjet operation. In this paper, shape optimization has been performed with surrogate-assisted evolutionary algorithms to maximize the thrust generated by an axisymmetric scramjet nozzle configuration, including the base flow and external surface for cruise conditions at Mach 8 at two altitudes with and without fuel. The optimization results have been examined in a coupled numerical/analytical approach in order to identify the key design factors and investigate the effects of design parameters. It has been found that the optimum nozzle geometries are characterized by bell-type shapes for the fuel-on conditions, whereas the optima for the fuel-off case feature nearly conical shapes. Their robustness in thrust production has been demonstrated by cross- referencing the optimum geometries at off-design altitudes. The nozzle length and radius have been found to be the most influential parameters in all considered conditions, with their optimum values determined based on the balance between inviscid and viscous force components, whereas the other parameters have minor impact on the total axial force. Copyright