Showing papers in "AIAA Journal in 2001"

Kriging Models for Global Approximation in Simulation-Based Multidisciplinary Design Optimization

Abstract: Response surface methods have been used for a variety of applications in aerospace engineering, particularly in multidisciplinary design optimization. We investigate the use of kriging models as alternatives to traditional second-order polynomial response surfaces for constructing global approximations for use in a real aerospace engineering application, namely, the design of an aerospike nozzle. Our objective is to examine the difeculties in building and using kriging models to create accurate global approximations to facilitate multidisciplinary design optimization. Error analysis of the response surface and kriging models is performed, along with a graphical comparison of the approximations. Four optimization problems are also formulated and solved using both sets of approximation models to gain insight into their use for multidisciplinary design optimization. We end that the kriging models, which use only a constant “global” model and a Gaussian correlation function, yield global approximations that are slightly more accurate than the response surface models.

Fifty Years of Shock-Wave/Boundary-Layer Interaction Research: What Next?

Abstract: Because of their ubiquitous presence in high-speed flight and their impact on vehicle and component performance, shock-wave/boundary-layer interactions have been studied for about 50 years. Despite truly remarkable progress in computational and measurement capabilities, there are still important quantities that cannot be predicted very accurately, that is, peak heating in strong interactions, or cannot be predicted at all, that is, unsteady pressure loads. There remain observations that cannot be satisfactorily explained and physical processes that are not well understood. Much work remains to be done. Based on the author's own views and those of colleagues, some suggestions are made as to where future efforts might be focused. Just as the first workers in the field could not have foreseen the capabilities generated by the computer/instrumentation revolution of the past 20 years, it is probably fair to assume that the extent of our vision and imagination in the year 2000 is equally limited. New simulation and measurement techniques will doubtlessly become available in the next 10 or 20 years, the results from which will render many of the current concerns moot

Aerodynamic Flow Control over an Unconventional Airfoil Using Synthetic Jet Actuators

Abstract: Control of flow separation on an unconventional symmetric airfoil using synthetic (zero net mass flux) jet actuators is investigated in a series of wind tunnel tests. The symmetric airfoil comprises the aft portion of a NACA four-digit series airfoil and a leading edge section that is one-half of a round cylinder. The experiments are conducted over a range of Reynolds numbers between 3.1 × 10 5 and 7.25 × 10 5 . In this range, the flow separates near the leading edge at angles of attack exceeding 5 deg. When synthetic jet control is applied near the leading edge, upstream of the separation point, the separated flow reattaches completely for angles of attack up to 17.5 deg and partially for higher angles of attack. The effect of the actuation frequency, actuator location, and momentum coefficient is investigated for different angles of attack. The momentum coefficient required to reattach the separated flow decreases as the actuators are placed closer to the separation point. In some cases, reattachment is also achieved when the actuators are placed downstream of the stagnation point on the pressure side of the airfoil

Survey of Shape Parameterization Techniques for High-Fidelity Multidisciplinary Shape Optimization

Abstract: A survey is provided of shape parameterization techniques formultidisciplinary optimization, and some emerging ideas are highlighted. The survey focuses on the suitability of available techniques for multidisciplinary applications of complex cone gurations using high-e delity analysis tools such as computational e uid dynamics and computational structural mechanics. The suitability criteria are based on the efe ciency, effectiveness, ease of implementation, and availability of analytical sensitivities for geometry and grids. A section on sensitivity analysis, grid regeneration, and grid deformation techniques is also provided.

Experimental and Theoretical Study on Aeroelastic Response of High-Aspect-Ratio Wings

Abstract: An experimental high-aspect-ratio wing aeroelastic model with a slender body at the tip has been constructed, and the response due to flutter and limit-cycle oscillations (LCO) has been measured in a wind-tunnel test A theoretical model has been developed and calculations made to correlate with the experimental data Structural equations of motion based on nonlinear beam theory are combined with the ONERA aerodynamic stall model to study the effects of geometric structural nonlinearity and steady angle of attack on flutter and LCO of high-aspect-ratio wings Static deformations in the vertical and torsional directions caused by a steady angle of attack and gravity are measured, and results from theory and experiment are compared A dynamic perturbation analysis about a nonlinear static equilibrium is used to determine the small perturbation flutter boundary, which is compared to the experimentally determined flutter velocity and oscillation frequency Time simulation is used to compute the LCO response The results between the theory and experiment are in good agreement for static aeroelastic response, the onset of flutter, and dynamic LCO amplitude and frequency

Stabilization of Hypersonic Boundary Layers by Porous Coatings

Abstract: A second-mode stability analysis has been performed for a hypersonic boundary layer on a wall covered by a porous coating with equally spaced cylindrical blind microholes. Massive reduction of the second mode amplification is found to be due to the disturbance energy absorption by the porous layer. This stabilization effect was demonstrated by experiments recently conducted on a sharp cone in the T-5 high-enthalpy wind tunnel of the Graduate Aeronautical Laboratories of the California Institute of Technology. Their experimental confirmation of the theoretical predictions underscores the possibility that ultrasonically absorptive porous coatings may be exploited for passive laminar flow control on hypersonic vehicle surfaces.

Extension to the Messinger Model for Aircraft Icing

Abstract: A one-dimensional mathematical model is developed describing ice growth due to supercooled e uid impacting on a solid substrate. When rime ice forms, the ice thickness is determined by a simple mass balance. The leadingorder temperature proe le through the ice is then obtained as a function of time, the ambient conditions, and the ice thickness. When glaze ice forms, the energy equation and mass balance are combined to provide a single e rst-order nonlinear differential equation for the ice thickness, which is solved numerically. Oncethe icethickness is obtained, the water height and the temperatures in the layers may be calculated. The method for extending the one-dimensional model to two and three dimensions isdescribed. Icegrowth rates and freezing fractions predicted by the current method are compared with the Messinger model. The Messinger model is shown to be a limiting case of the present method.

Sensitivity Analysis for Navier-Stokes Equations on Unstructured Meshes Using Complex Variables

Abstract: The use of complex variables for determining sensitivity derivatives for turbulent flows is examined. Although a step size parameter is required, the numerical derivatives are not subject to subtractive cancellation errors and, therefore, exhibit true second-order accuracy as the step size is reduced. As a result, this technique guarantees two additional digits of accuracy each time the step size is reduced one order of magnitude. This behavior is in contrast to the use of finite differences, which suffer from inaccuracies due to subtractive cancellation errors. In addition, the complex-variable procedure is easily implemented into existing codes

Grid Convergence Error Analysis for Mixed-Order Numerical Schemes

Abstract: New developments are presented in the area of grid convergence error analysis and error estimation for mixed-order numerical schemes. A mixed-order scheme is defined here as a numerical method where the order of the local truncation error varies either spatially (e.g., at a shock wave) or for different terms in the governing equations (e.g., first-order convection with second-order diffusion). The case examined herein is the Mach 8 laminar flow of a perfect gas over a sphere-cone geometry. This flowfield contains a strong bow shock wave where the formally second-order numerical scheme is reduced to first order via a flux limiting procedure. The mixedorder error analysis method allows for non-monotone behavior in the solutions variables as the mesh is refined. Non-monotonicity in the local solution variables is shown to arise from a cancellation of first- and second-order error terms for the present case. The proposed error estimator, which is based on the mixed-order analysis, is shown to provide good estimates of the actual error. Furthermore, this error estimator nearly always provides conservative error estimates, in the sense that the actual error is less than the error estimate, for the case examined.

Simulation of Flow About Flapping Airfoils Using Finite Element Incompressible Flow Solver

Abstract: Ae niteelemente owsolverbasedonunstructuredgridsisemployedforstudyingtheunsteadye owpastoscillating airfoils. The viscous e ow past a NACA0012 airfoil at various pitching frequencies is simulated. The variation of the force coefe cient with reduced frequency is compared to experimental and other numerical studies. The effect of variation of the amplitude of the pitching motion on the force coefe cient shows that the critical parameter for thrust generation is not the reduced frequency but the Strouhal number based on the maximum excursion of the trailing edge. The e ow about theairfoil in a combined pitching and heaving motion, a modefound in many insects, is also simulated. The effects of varying the phase angle between the pitch and the heave motions is studied. The thrust coefe cient was compared with experimental studies and good agreement is obtained. It is found that the maximumthrustcoefe cient isobtained forwhen thepitchmotionleads theheavemotion by 120 deg andmaximum propulsive efe ciency occurs at a phase angle of 90 deg.

Coupled Analytical Sensitivity Analysis and Optimization of Three-Dimensional Nonlinear Aeroelastic Systems

Abstract: We consider the problem of optimizing for steady-state conditions a given nonlinear aeroelastic system, by varying both aerodynamic and structural parameters. We model the structure by e nite elements and predict the aerodynamic loads by a three-dimensional e nite volume approximation of the Euler equations. We present a complete optimization methodology whose key components are a computer aided geometric design method for representing the design, an analytical approach for sensitivity analysis, a gradient-based optimization algorithm and two staggered schemes for evaluating the aeroelastic responses and solving the coupled sensitivity equations. We illustrate our methodology and demonstrate its potential with various aeroelastic optimizations of idealized and builtup wing structures.

Large-Eddy Simulation of a Supersonic Boundary Layer Using an Unstructured Grid

Abstract: A Mach 3 adiabatic flat plate turbulent boundary layer is studied using large-eddy simulation (LES). The filtered compressible Navier-Stokes equations are solved on a three-dimensional unstructured grid of tetrahedral cells. A compressible extension of the rescaling-reintroducing process of Lund et al. is developed to generate the inflow conditions. The effect of the subgrid-scale motion is incorporated using two approaches, namely, monotone integrated LES (MILES) and the Smagorinsky subgrid-scale model. A detailed grid refinement study is performed

Structure, penetration, and mixing of pulsed jets in crossflow

Abstract: Effects of periodic disturbances on the structure and mixing of a transverse jet have been investigated through chemically reactive laser-induced fluorescence experiments in a water model. Flow visualization experiments with a steady, round jet in crossflow revealed a distinct vortex loop merging pattern among the vortices that make up the curved shear layer around the jet. As the vortex loops are stretched and distorted, certain parts of the neighboring loops with the opposite or the same sign of vorticity merge, resulting in cancellation or intensification of the vorticity in the corresponding regions of the jet. When the flow rate of this jet was periodically modulated by a square wave, however, distinct vortex rings were created whose spacing and strength were dictated by the pulsing frequency for a given jet and crossflow combination. At low pulsing rates, these rings penetrated into the crossflow significantly deeper than the steady jet. An optimum pulsing frequency was found at which closely spaced vortex rings were observed, which penetrated as discrete vortices into the crossflow in the near field. Strong interactions among neighboring rings were observed farther downstream

Characteristic Constraint Modes for Component Mode Synthesis

Abstract: A technique is presented for reducing the size of a model generated by the Craig-Bampton method (Craig, R. R., and Bampton, M. C. C., Coupling of Substructures for Dynamic Analyses, AIAA Journal, Vol. 6, No. 7, 1968, pp. 1313-1319) of component mode synthesis (CMS). An eigenanalysis is performed on the partitions of the CMS mass and stiffness matrices that correspond to the so-called constraint modes. The resultant eigenvectors are referred to as characteristic constraint modes because they represent the characteristic motion of the interface between the component structures. When the characteristic constraint modes are truncated, a CMS model with a highly reduced number of degrees of freedom may be obtained. An example of a cantilever plate is considered. It is shown that relatively few characteristic constraint modes are needed to yield accurate approximations of the lower natural frequencies. Furthermore, this method yields physical insight into the mechanisms of vibration transmission in complex structures, and it provides an excellent framework for the efficient calculation of power flow.

Similarity Analysis for Turbulent Boundary Layer with Pressure Gradient: Outer Flow

Abstract: The equilibrium-type similarity analysis of George and Castillo for the outer part of zero pressure gradient boundary layers has been extended to include boundary layers with pressure gradient. The constancy of a single new pressure gradient parameter is all that is necessary to characterize these new equilibrium turbulent boundary layers. Three major results are obtained: First, most pressure gradient boundary experiments appear to be equilibrium flows (by the new definition), and nonequilibrium flows appear to be the exception. Second, there appear to be only three values of the pressure gradient parameter: one for adverse pressure gradients, one for favorable pressure gradients, and one for zero pressure gradients. Third, correspondingly, there appear to be only three normalized velocity deficit profiles, exactly as suggested by the theory

Reduced-Order Models for Nonlinear Unsteady Aerodynamics

Abstract: Two reduced-order modeling approaches for the evaluation of nonlinear aerodynamic forces based on CFD computations are presented. These reducedorder models (ROMs) provide a means for rapid calculation of frequency-domain generalized aerodynamic forces, which can be used in traditional flutter analysis scheme, to calculate flutter characteristics about nonlinear steady flows. Two ROMs are presented, one that is based on the Volterra theory for nonlinear systems, and a new ROM that is based on step (indicial) responses. ROM kernels are identified directly from input-output relations, and the study focuses on issues of kernel identification and their effect on the quality of the ROM. First- and second-order ROMs are generated for the response of the AGARD 445.6 wing to forced-harmon ic excitation of its elastic modes. Responses computed from the ROMs are compared to responses obtained directly from a CFD analysis in which the boundary conditions are excited harmonically. Results show that the quality of the Volterra ROM is very sensitive to the amplitudes of the impulse inputs used for identification. The step-response ROM is shown to be more accurate than the Volterra ROM and less sensitive to the amplitude used for its identification.

Large-Eddy Simulation of Supersonic Compression-Ramp Flow by High-Order Method

Abstract: A high-order method is used to perform large-eddy simulations of a supersonic compression-ramp flowfield. The procedure employs an implicit approximately factored finite difference algorithm, which is used in conjunction with a 10th-order nondispersive filter. Spatial derivatives are approximated by a sixth-order compact scheme, and Newton-like subiterations are applied to achieve second-order temporal accuracy. In the region of strong shock waves, the compact differencing of convective fluxes is replaced locally by an upwind-biased scheme. Both the Smagorinsky and dynamic subgrid-scale stress models are incorporated in the simulations. Details of the method are summarized, and a number of computations are carried out. Comparisons are made between the respective solutions as well as with available experimental data and with previous numerical results

Random Packing of Heterogeneous Propellants

Abstract: A random packing algorithm is implemented to construct numerically models of heterogeneous propellants. These models consist of random distributions of spheres in a periodic cube. The spheres can have various sizes, randomly assigned if desired. Packing fractions are calculated for a bimodal model (spheres of two different sizes) and compare well with old experimental data for steel shot. Slices through the cube dee ne surfaces that represent propellant surfaces, and the stoichiometry of these surfaces is a stochastic variable. Several realizations of the propellant cube are constructed and variations in surface stoichiometry are examined using histograms and Fourierseries.Asamplee amecalculation ispresented andsolved using datadee ned by a singlesurfacerealization.

Design Potential Method for Robust System Parameter Design

Abstract: A novel design potential method that integrates the probabilistic constraint evaluation closely into the design optimization process is presented for robust system parameter design. From a broader perspective, it is shown that the probabilistic constraints can be evaluated using either the conventional reliability index approach or the proposed performance measure approach. The performance measure approach is inherently robust and is more effective when the prohahilistic constraint is inactive. The reliability index approach is more effective for the violated probabilistic constraint, but it could yield singularity when the probabilistic constraint is inactive. Moreover, the close coupling of performance probability analysis and design optimization is illustrated in a proposed unified system space. The design potential method, which is developed to take full advantage of the important design information obtained from the previous probabilistic constraint evaluation, can significantly accelerate the convergence of the reliability-based design optimization process.

Chemistry of JP-10 Ignition

Abstract: Ignition of JP-10 is addressed from computational and theoretical viewpoints. A detailed chemical mechanism consisting of 174 elementary steps among 36 chemical species is obtained by adding 27 steps, including JP-10, cyclopentene, and 1,3 butadiene, to an earlier system of 147 steps among 33 species that extend through C 3 hydrocarbons. The new steps and their rate parameters are derived by analogy with earlier studies of decane and heptane. Predictions of ignition times by the new detailed mechanism are found to be in good agreement with data from JP-10 shock-tube experiments. Systematically reduced mechanisms also are discussed on the basis of the detailed mechanism, resulting in a simplified correlation that performs well. The results can be helpful for applications in airbreathing propulsion involving JP-10.

Organized Oscillations of Initially-Turbulent Flow Past a Cavity

Abstract: Flow past an open cavity is known to give rise to self-sustained oscillations in a wide variety of configurations, including slotted-wall, wind and water tunnels, slotted flumes, bellows-type pipe geometries, high-head gates and gate slots, aircraft components and internal piping systems. These cavity-type oscillations are the origin of coherent and broadband sources of noise and, if the structure is sufficiently flexible, flow-induced vibration as well. Moreover, depending upon the state of the cavity oscillation, substantial alterations of the mean drag may be induced. In the following, the state of knowledge of flow past cavities, based primarily on laminar inflow conditions, is described within a framework based on the flow physics. Then, the major unresolved issues for this class of flows will be delineated. Self-excited cavity oscillations have generic features, which are assessed in detail in the reviews of Rockwell and Naudascher, Rockwell, Howe and Rockwell. These features, which are illustrated in the schematic of Figure 1, are: (i) interaction of a vorticity concentration(s) with the downstream corner, (ii) upstream influence from this corner interaction to the sensitive region of the shear layer formed from the upstream corner of the cavity; (iii) conversion of the upstream influence arriving at this locationmore » to a fluctuation in the separating shear layer; and (iv) amplification of this fluctuation in the shear layer as it develops in the streamwise direction. In view of the fact that inflow shear-layer in the present investigation is fully turbulent, item (iv) is of particular interest. It is generally recognized, at least for laminar conditions at separation from the leading-corner of the cavity, that the disturbance growth in the shear layer can be described using concepts of linearized, inviscid stability theory, as shown by Rockwell, Sarohia, and Knisely and Rockwell. As demonstrated by Knisely and Rockwell, on the basis of experiments interpreted with the aid of linearized theory, not only the fundamental component of the shear layer instability may be present, but a number of additional, primarily lower frequency components can exist as well. In fact, the magnitude of these components can be of the same order as the fundamental component. These issues have not been addressed for the case of a fully-turbulent in-flow and its separation from the leading corner of the cavity.« less

Time Response of Anodized Aluminum Pressure-Sensitive Paint

Abstract: The response time of anodized aluminum pressure-sensitive paint (AA-PSP) was studied to develop the capability of making global pressure measurements in unsteady flow conditions. This pressure-sensitive paint (PSP) uses anodized aluminum as a porous supporting matrix, which improves the response time by increasing the oxygen diffusion process in the PSP layer. A response time of 34.8 μs was obtained from AA-PSP with 4.3-μm matrix thickness. Response times of PSPs were measured from a step change of pressure created by a normal shock wave in a shock tube. The response time of AA-PSP is dependent on the matrix thickness, with a thin supporting matrix giving a fast response time. The increase in surface temperature of the paint caused by shock waves was also measured using a temperature-sensitive paint (rhodamine-B on anodized aluminum) to understand the temperature effect of AA-PSP

Unsteady Flow Evolution in Porous Chamber with Surface Mass Injection, Part 1: Free Oscillation

Abstract: Unsteadye owevolutioninaporouschamberwithsurfacemassinjectionsimulatinganozzlelessrocketmotorhas been investigated numerically. The analysis is based on a large-eddy-simulation technique in which the spatially e ltered and Favre averaged conservation equations for large, energy-carrying turbulent structures are solved explicitly. The effect of the unresolved scales is modeled semi-empirically by considering adequate dissipation rates for the energy present in the resolved scale motions. The e owe eld is basically governed by the balance between the inertia force and pressure gradient, as opposed to viscouseffects and pressuregradient corresponding to channel e ows without transpiration. It accelerates from zero at the head end and becomes supersonic in the divergent section of the nozzle. Three successive regimes of development, laminar, transitional, and fully turbulent e ow, are observed. Transition to turbulence occurs away from the porous wall in the midsection of the motor, and the peak in the turbulence intensity moves closer to the wall farther downstream as the local Reynolds number increases. Increase in pseudoturbulence level at the injection surface causes early transition to turbulence. As the e ow develops farther downstream, the velocity proe le transits into the shape of a fully developed turbulent pipe e ow with surface transpiration. The compressibility effect also plays an important role, causing transition of the mean velocity proe les from their incompressible e ow counterparts as the local Mach number increases. The e ow evolution is characterized primarily by three nondimensional numbers: injection Reynolds number, centerline Reynolds number, and momentum e ux coefe cient.

Optimized Nonuniform Rational B-Spline Geometrical Representation for Aerodynamic Design of Wings

Abstract: The geometric representation and parameterization used in an aerodynamic wing design process determines the number of design variables and influences the smoothness of the wing representation. In an attempt to reduce the number of design variables while preserving good smoothness properties, the present research investigates the performance of an optimized nonuniform rational B-spline (NURBS) geometrical representation for the aerodynamic design of wings. As a first step, an approach is described whereby optimal spatial positions and weights of a fixed number of NURBS control points is determined using a quasi-Newton optimization algorithm to approximate a general airfoil section. The resulting optimized NURBS representation significantly reduces the number of design variables needed to define accurately a wing section while ensuring good smoothness properties. In a second step, the NURBS control point positions and weights are used as design variables in an aerodynamic optimization problem. This methodology results in a rapid and robust design process, as illustrated by examples of aerodynamic optimization for two- and three-dimensional cases

Accuracy of Pressure-Sensitive Paint

Abstract: Uncertainty in pressure sensitive paint (PSP) measurement is investigated from a standpoint of system modeling. A functional relation between the imaging system output and luminescent emission from PSP is obtained based on studies of radiative energy transports in PSP and photodetector response to luminescence. This relation provides insights into physical origins of various elemental error sources and allows estimate of the total PSP measurement uncertainty contributed by the elemental errors. The elemental errors and their sensitivity coefficients in the error propagation equation are evaluated. Useful formulas are given for the minimum pressure uncertainty that PSP can possibly achieve and the upper bounds of the elemental errors to meet required pressure accuracy. An instructive example of a Joukowsky airfoil in subsonic flows is given to illustrate uncertainty estimates in PSP measurements.

Directional Suppression of Noise from a High-Speed Jet

Abstract: Experiments demonstrate directional suppression of noise from a high-speed jet using an asymmetric parallel secondary stream. The secondary stream attenuates Mach wave radiation in the lower hemisphere of the acoustic far eeld, leaving unaltered the upward-propagated Mach waves. An eccentric nozzle arrangement with a Mach 1.5, 700-m/s inner stream and a Mach 1.0, 360-m/s outer stream produces noise reduction superior to that from concentric arrangements or from the fully mixed equivalent jet. The angle of peak perceived noise shifts from the aft quadrant to the lateral direction. The beneet of the eccentric arrangement is attributed to its shorter potential core relative to a concentric jet. The experiments also reveal emission of strong crackle from the untreated jet, a noise component arising from the nonlinearity of Mach waves. The secondary eow suppresses crackle.

Active-Control System for Breakup of Airplane Trailing Vortices

Abstract: Wing control surfaces are used to trigger the breakup of trailing vortices behind aircraft in a flaps-down configuration. In the near field of the aircraft there are multiple pairs of vortices, which admit new instability mechanisms that do not exist on a single pair of vortices. A periodic motion of the control surfaces is used to introduce a unique form of perturbation that is amplified in the multiple vortex-pair system but conserves total circulation, lift, and rolling moment. Growth of the perturbations leads to the periodic pinching of the starboard and port vortices into a series of vortex rings. The concept is demonstrated using numerical simulations and towing-tank experiments. Results show that the system breaks up the trailing vortices more rapidly than a comparable excitation of the Crow instability on a single pair of vortices. The overall effectiveness of the system depends on the airplane configuration, namely, details of the flap system and the horizontal tail

Aerodynamic Optimization of Supersonic Transport Wing Using Unstructured Adjoint Method

Abstract: In the application of gradient-based methods to practical aerodynamic design problems, one of the major concerns is an accurate and efficient calculation of sensitivity derivatives of an aerodynamic objective function. Sensitivity derivatives can be evaluated robustly and efficiently by using a sensitivity analysis code based either on a direct method or on an adjoint method. An adjoint method is preferable in aerodynamic designs because it is more economical when the number of design variables is larger than the total number of an objective function and constraints.

Electron-Beam-Generated Plasmas in Hypersonic Magnetohydrodynamic Channels

Abstract: A novel concept is analyzed of hypersonic cold-air magnetohydrodynamic (MHD) power generators and accelerators with ionization by electron beams. Ionization processes are considered in detail. Strong coupling between hypersonic boundary layers and electrode sheaths is demonstrated, and anode voltage fall in hypersonic MHD channels is shown to be very high. A potential anode sheath instability and ways to suppress it are discussed. Electron beams are shown to be capable of generating an adequate conductivity in cold air, while allowing full control and stable operation of MHD channels. Example calculations of hypersonic accelerator and power generator performance appear to be promising.