Paul I. King

In-Stream Hypermixer Fueling Pylons in Supersonic Flow

This paper presents results from both computational fluid dynamic and wind-tunnel experiments of in-stream fueling pylons injecting air, ethylene, and methane gas into Mach number 2.0 cold airflow. Three fuel-injection pylons studied include a basic pylon, a ramp pylon, and an alternating-wedge pylon. The latter two pylons introduce streamwise vorticity into the flow to increase mixing action. The computational fluid dynamic solution was accomplished using the commercial code FLUENT®. Three wind-tunnel experimental techniques were used: aerothermal probing, Raman spectroscopy, and nitric-oxide planar laser-induced fluorescence. Four measures reported include streamwise vorticity, total-pressure-loss, mixing efficiency, and flammable plume extent. The ramp and alternating-wedge pylons show decisive increases in mixing capability compared with the basic pylon for a finite distance downstream of the injector. The alternating-wedge pylon exhibits a measurable increase in total pressure loss compared with the basic pylon, and the ramp pylon exhibits a negligible increase in total pressure loss compared with the basic pylon. For comparison, the downstream mixing effectiveness of the three pylons is compared with the downstream mixing effectiveness of a transverse circular wall injector studied in past research. In addition, a qualitative comparison between the computational fluid dynamic and wind-tunnel experimental results is made.

Reduced order modeling of a two-dimensional flow with moving shocks

Abstract The objective of this paper is to demonstrate the ability of proper orthogonal decomposition, in combination with domain decomposition, to produce accurate reduced order models (ROMs) for two-dimensional high-speed flows with moving shock waves. To demonstrate this ability, a blunt body flow with quasi-steady shock motion is considered. The blunt body flow contains a strong bow shock that is moved via a change in inlet Mach number and angle of attack. Accuracy is quantified by comparing surface pressures obtained from the ROMs with those from the full order simulation under the same free stream conditions. The order reduction, and computational performance of the ROM is also quantified relative to the full order simulation. The robustness of the ROM to varying flow parameters is explored. A non-Galerkin quasi-implicit steady state implementation is considered.

Swept-Leading-Edge Pylon Effects on a Scramjet Pylon-Cavity Flameholder Flowfield

This study explores the effect of adding a pylon to the leading edge of a cavity flameholder in a scramjet combustor. Data were obtained through a combination of wind-tunnel experimentation and steady-state computational fluid dynamics. Wind-tunnel data were collected using surface pressure taps, static and total probe data, shadowgraph flow visualization, and particle image velocimetry. Computational fluid dynamics models were solved using the commercial FLUENT software. The addition of an intrusive device to the otherwise low-drag cavity flamebolder offers a potential means of improving combustor performance by enabling combustion products to propagate into the main combustor flow via the low-pressure region behind the pylon. This study characterized the flowfield effects of adding the pylon as well as the effect of changing Reynolds numbers over the range of approximately 33 x 10 6 to 55 × 10 6 m ―1 at a Mach number of 2. The addition of the pylon resulted in approximately 3 times the mass flow passing through the cavity compared with the cavity with no pylon installed. Reynolds number effects were weak. The addition of the pylon led to the cavity fluid traveling up to the top of the pylon wake and significantly increasing the exposure and exchange of cavity fluid with the main combustor flow.

Applications of multi-POD to a pitching and plunging airfoil

Multi-POD is a new proper orthogonal decomposition (POD) based reduced order modeling (ROM) technique for modeling flows on deforming grids. Presented is the application of multi-POD to flow about a pitching and plunging airfoil. The multi-POD technique expands the parameter space in which POD is applied through selection of the best available ROM for a given set of grid deformations. For application to unconstrained pitching and plunging motion of an airfoil, multi-POD is shown to be effective when trained for forced grid motion, reducing the training requirements significantly. A three-orders of magnitude reduction in the number of degrees of freedom is also shown in the use of POD/ROM for the aeroelastic problem.

Airfoil Pitch-and-Plunge Bifurcation Behavior with Fourier Chaos Expansions

A stochastic projection method is employed to obtain the probability distribution of pitch angle of an airfoil in pitch and plunge subject to probabilistic uncertainty in both the initial pitch angle and the cubic spring coefficient of the restoring pitch force. Historically, the selected basis for the stochastic projection method has been orthogonal polynomials, referred to as the polynomial chaos. Such polynomials, however, result in unacceptable computational expense for applications involving oscillatory motion, and a new basis, the Fourier chaos, is introduced for computing limit-cycle oscillations. Unlike the polynomial chaos expansions, which cannot predict limit-cycle oscillations, the Fourier chaos expansions predict both subcritical and supercritical responses even with low-order expansions and high-order nonlinearities. Bifurcation diagrams generated with this new approximate method compare well to Monte Carlo simulations.

POD-Based reduced-order models with deforming grids

Proper orthogonal decomposition based reduced order modeling (POD/ROM) is examined with deforming grids. POD/ROM is a technique that operates in an index-space for computations, not typically accounting for grid dynamics. Two model problems are presented to demonstrate the method of accounting for the effects of grid deformation on POD/ROM. The analytical solution of flow about an oscillating cylinder and potential flow over an oscillating panel. The accuracy and robustness of POD/ROM on deforming grids are compared to that of rigid grid POD/ROM. Deforming grid POD/ROMs are found to require more modes than rigid grid POD/ROMs for similar accuracy levels. In addition, for deforming grids, POD/ROMs are less accurate when the grid deformation is significantly altered from the deformations seen in the POD/ROM development. To address these issues, a new technique is developed that compares the relative grid motion between the POD/ROM creation and execution. The technique determines the current relative grid deformation and selects the best POD/ROM from those available.

Experimental Studies of Pylon-Aided Fuel Injection into a Supersonic Crossflow

Abstract : An investigation of the nonreacting flow associated with pylon-aided gaseous fuel injection into a Mach 2 crossflow is described. In this study, a small pylon was positioned just upstream of a circular flush-wall fuel injector. Three pylon geometries were studied, along with a no-pylon reference case. In all cases, a typical cavity-based flameholder was positioned downstream of the fuel injector. The injectant plume characteristics were interrogated using a variety of laser-based and probe-based measurement techniques. Planar laser-induced fluorescence of nitric oxide was used to study the instantaneous plume structure. Spontaneous vibrational Raman scattering provided time-averaged plume characteristics and mixing information. Probe-based instrumentation was used in conjunction with the mixing data to estimate the total pressure losses associated with each configuration. Each pylon had a unique influence on the fuel-injection plume. In all cases, the presence of the pylon resulted in improved fuel penetration into the supersonic crossflow without significantly changing the total pressure-loss characteristics. Mixing efficiencies of the pylon-aided injection cases were not substantially different from the reference case.

Experimental Investigation of Stepped Tip Gap Effects on the Performance of a Transonic Axial-Flow Compressor Rotor

The effects of stepped-tip gaps and clearance levels on the performance of transonic axial-flow compressor rotor were experimentally determined. A two-stage compressor with no inlet guide vanes was tested in a modern transonic compressor research facility. The first-stage rotor was unswept and was tested for an optimum tip clearance with variations in stepped gaps machined into the casing near the aft tip region of the rotor. Nine casing geometries were investigated consisting of three step profiles at each of three clearance levels. For small and intermediate clearances, stepped tip gaps were found to improve pressure ratio, efficiency, and flow range for most operating conditions. At 100 percent design rotor speed, stepped tip gaps produced a doubling of mass flow range with as much as a 2.0 percent increase in mass flow and a 1.5 percent improvement in efficiency. This study provides guidelines for engineers to improve compressor performance for an existing design by applying an optimum casing profile.

Reduced-order modeling of an elastic panel in transonic flow

Reduced-order modeling is applied to a transonic aeroelastic panel that experiences oscillatory motions of a normal shock. Two-dimensional, transonic inviscid flow over an elastic panel produces transonic limit-cycle oscillations over a range of panel parameters. Proper orthogonal decomposition, in concert with domain decomposition, is shown to produce an accurate reduced-order model for the coupled aeroelastic system. Panel flutter in the transonic regime results in a large streamwise movement of a transonic normal shock across the panel surface. The accuracy and order reduction of the reduced-order model is quantified. In addition, the computational savings for this implementation is documented, and the robustness of the reduced-order model to changes in a panel parameter is explored.

Propagation of Detonation Waves in Tubes Split from a PDE Thrust Tube

Abstract : A Pulse Detonation Engine (PDE) combusts a fuel air mixture through detonation. Existing designs require spark plugs in each separate thrust tube to ignite premixed reactants. A single thrust tube could require the spark plug to fire hundreds of times per second for long durations. This paper reports on the use of a continuously propagating detonation wave as both a thrust producer and a single ignition source for a multi-tube system. The goal was to minimize ignition complexity and increase reliability by limiting the number of ignition sources. The work includes a systematic investigation of single tube geometric effects on detonations. These results were subsequently used to further examine conditions for splitting detonations i.e. the division of a detonation wave into two separate detonation waves. Einally a dual thrust tube system was built and tested that successfully employed a single spark to initiate detonation in separate thrust tubes.