Showing papers on "Supersonic speed published in 2002"

High-Fidelity Aerostructural Design Optimization of a Supersonic Business Jet

Abstract: This paper focuses on the demonstration of an integrated aerostructural method for the design of aerospace vehicles. Both aerodynamics and structures are represented using high-fidelity models such as the Euler equations for the aerodynamics and a detailed finite element model for the primary structure. The aerodynamic outer-mold line and a structure of fixed topology are parameterized using a large number of design variables. The aerostructural sensitivities of aerodynamic and structural cost functions with respect to both outer-mold line shape and structural variables are computed using an accurate and efficient coupled-adjoint procedure. Kreisselmeier‐ Steinhauser functions are used to reduce the number of structural constraints in the problem. Results of the aerodynamic shape and structural optimization of a natural laminar-flow supersonic business jet are presented together with an assessment of the accuracy of the sensitivity information obtained using the coupled-adjoint procedure.

Laboratory Astrophysics and Collimated Stellar Outflows: The Production of Radiatively Cooled Hypersonic Plasma Jets

Abstract: We present the first results of astrophysically relevant experiments where highly supersonic plasma jets are generated via conically convergent flows. The convergent flows are created by electrodynamic acceleration of plasma in a conical array of fine metallic wires (a modification of the wire array Z-pinch). Stagnation of plasma flow on the axis of symmetry forms a standing conical shock effectively collimating the flow in the axial direction. This scenario is essentially similar to that discussed by Canto and collaborators as a purely hydrodynamic mechanism for jet formation in astrophysical systems. Experiments using different materials (Al, Fe, and W) show that a highly supersonic (M ~ 20), well-collimated jet is generated when the radiative cooling rate of the plasma is significant. We discuss scaling issues for the experiments and their potential use for numerical code verification. The experiments also may allow direct exploration of astrophysically relevant issues such as collimation, stability, and jet-cloud interactions.

Detached-eddy simulation with compressibility corrections applied to a supersonic axisymmetric base flow

Abstract: Detached-eddy simulation is applied to an axisymmetric base flow at supersonic conditions. Detached-eddy simulation is a hybrid approach to modeling turbulence that combines the best features of the Reynolds-averaged Navier-Stokes and large-eddy simulation approaches. In the Reynolds-averaged mode, the model is currently based on either the Spalart-Allmaras turbulence model or Menter’s shear stress transport model; in the largeeddy simulation mode, it is based on the Smagorinski subgrid scale model. The intended application of detached-eddy simulation is the treatment of massively separated, highReynolds number flows over complex configurations (entire aircraft, automobiles, etc.). Because of the intented future application of the methods to complex configurations, Cobalt, an unstructured grid Navier-Stokes solver, is used. The current work incorporates compressible shear layer corrections in both the Spalart-Allmaras and shear stress transport-based detached-eddy simulation models. The effect of these corrections on both detached-eddy simulation and Reynolds-averaged Navier-Stokes models is examined, and comparisons are made to the experiments of Herrin and Dutton. Solutions are obtained on several grids—both structured and unstructured—to test the sensitivity of the models and code to grid refinement and grid type. The results show that predictions of base flows using detached-eddy simulation compare very well with available experimental data, including turbulence quantities in the wake of the axisymmetric body. @DOI: 10.1115/1.1517572#

A Numerical Characterization of Particle Beam Collimation by an Aerodynamic Lens-Nozzle System: Part I. An Individual Lens or Nozzle

Abstract: Particle beams have traditionally been produced by supersonic expansion of a particle-laden gas through a single nozzle to vacuum However, it has been shown that, by passing the particle-laden gas

X-ray Imaging of Shock Waves Generated by High-Pressure Fuel Sprays

Abstract: Synchrotron x-radiography and a fast x-ray detector were used to record the time evolution of the transient fuel sprays from a high-pressure injector. A succession of 5.1-microsecond radiographs captured the propagation of the spray-induced shock waves in a gaseous medium and revealed the complex nature of the spray hydrodynamics. The monochromatic x-radiographs also allow quantitative analysis of the shock waves that has been difficult if not impossible with optical imaging. Under injection conditions similar to those found in operating engines, the fuel jets can exceed supersonic speeds and result in gaseous shock waves.

Scaling relations of supersonic turbulence in star-forming molecular clouds

Abstract: We present a direct numerical and analytical study of driven supersonic magnetohydrodynamic turbulence that is believed to govern the dynamics of star-forming molecular clouds. We describe statistical properties of the turbulence by measuring the velocity difference structure functions up to the fifth order. In particular, the velocity power spectrum in the inertial range is found to be close to Ek ~ k-1.74, and the velocity difference scales as |Δu| ~ L0.42. The results agree well with the Kolmogorov-Burgers analytical model suggested for supersonic turbulence.We then generalize the model to more realistic, fractal structure of molecular clouds and show that depending on the fractal dimension of a given molecular cloud, the theoretical value for the velocity spectrum spans the interval [-1.74, -1.89], while the corresponding window for the velocity difference scaling exponent is [0.42, 0.78].

Application of Large-Eddy Simulation to Supersonic Compression Ramps

Abstract: Large-eddy simulations of supersonic compression-ramp flowfields were performed by a high-order numerical method, utilizing the Smagorinsky dynamic subgrid-scale model to account for spatially underresolved stresses. Computations were carried out at a freestream Mach number of 3.0 for ramp angles of 8, 16, 20, and 24 deg. Extensive comparisons are made between the respective solutions and available experimental data that were collected at higher Reynolds numbers. These include surface pressure, skin friction, and both mean and fluctuating velocity profiles. For the 24-deg case, a number of experimentally measured statistical quantities are compared to the simulation

Scaling parameters for underexpanded supersonic jets

Abstract: An analysis and experiments were carried out to study the spreading and centerline property decay rates of underexpanded supersonic jets. The main purpose was to determine a suitable set of normalization parameters that would account for the initial expansion process and allow for a comparison of the asymptotic mixing rates of jets within a large range of exit-to-ambient pressure ratios. A set of expressions were developed for after-expansion equivalent jet exit diameter, velocity, temperature, and density to allow for a better collapse of jet spreading and centerline decay rates. Measurements were made for five different underexpanded sonic jets with jet exit-to-ambient pressure ratios of p e /p a =1, 2.5, 7.5, 15.5, and 20.3, corresponding to (isentropically) fully expanded jet Mach numbers of M j =1, 1.68, 2.38, 2.85, and 3.03, respectively. For each jet, both centerline and profile measurements were made using special probes that simultaneously measured local total pressure, static pressure, total temperature in the jet, as well as ambient conditions. These measurements were made in the subsonic flow regime, in some cases, extending as far as 270 nozzle diameters from the exit plane. The experimental results were analyzed and the asymptotic jet properties were determined using the new renormalization parameters.

Navier-Stokes Optimization of Supersonic Wings with Four Objectives Using Evolutionary Algorithm

Abstract: The design optimization of wings for supersonic transport by means of Multiobjective Evolutionary Algorithms is presented. Three objective functions are first considered to minimize the drag for transonic cruise, the drag for supersonic cruise and the bending moment at the wing root at the supersonic condition. The wing shape is defined by planform, thickness distributions and warp shapes in total of 66 design variables. A Navier-Stokes code is used to evaluate the aerodynamic performance at both cruise conditions. Based on the results, the optimization problem is further revised. The definition of the thickness distributions is given more precisely by adding control points. In total 72 design variables are used. The fourth objective function to minimize the pitching moment is added. The results of the revised optimization are compared with the three-objective optimization results as well as NAL’s design. Two Pareto solutions are found superior to NAL’s design for all four objective functions. The planform shapes of those solutions are “Arrow wing” type.

The connection between sound production and jet structure of the supersonic impinging jet

Abstract: An experimental investigation into the sound-producing characteristics of moderately and highly underexpanded supersonic impinging jets exhausting from a round convergent nozzle is presented The production of large plate tones by impingement on a square plate with a side dimension equal to 12 nozzle exit diameters is studied using random and phase-locked shadowgraph photography Discrete frequency sound is produced in the near-wall region of the jet when a Mach disk occurs upstream of the standoff shock wave Tones cease when the plate distance is approximately 22 free-jet cell lengths and the first and second shock waves are located in the free-jet positions The production of impulsive sound appears to be associated with the collapse of the standoff shock wave during a portion of the oscillation cycle Results from unsteady plate-pressure measurements indicate that plane-wave motion occurs in the impingement region and a secondary pressure maximum is observed on the plate adjacent to the flow region where sound appears to originate

Multimode Approach to Nonlinear Supersonic Flutter of Imperfect Circular Cylindrical Shells

Abstract: The aeroelastic stability of simply supported, circular cylindrical shells in supersonic flow is investigated by using both linear aerodynamics (first-order piston theory) and nonlinear aerodynamics (third-order piston theory). Geometric nonlinearities, due to finite amplitude shell deformations, are considered by using the Donnell's nonlinear shallow-shell theory, and the effect of viscous structural damping is taken into account. The system is discretized by Galerkin method and is investigated by using a model involving up to 22 degrees-of-freedom, allowing for travelling-wave flutter around the shell and axisymmetric contraction of the shell. Asymmetric and axisymmetric geometric imperfections of circular cylindrical shells are taken into account. Numerical calculations are carried out for a very thin circular shell at fixed Mach number 3 tested at the NASA Ames Research Center. Results show that the system loses stability by travelling-wave flutter around the shell through supercritical bifurcation. Nonsimple harmonic motion is observed for sufficiently high post-critical dynamic pressure. A very good agreement between theoretical and existing experimental data has been found for the onset of flutter, flutter amplitude, and frequency. Results show that onset of flutter is very sensible to small initial imperfections of the shells. The influence of pressure differential across the shell skin has also been deeply investigated. The present study gives, for the first time, results in agreement with experimental data obtained at the NASA Ames Research Center more than three decades ago. ©2002 ASME

Experimental and Computational Investigation of Supersonic Impinging Jets

Abstract: The results of an experimental and computational study of a moderately underexpanded axisymmetric supersonicjetissuingfroma convergingnozzleand impingingonagroundplanearepresented.Thegoalofthisworkisto develop a better understanding oftheimpinging jet e owe eld, which is of signie cantpracticalinterestbecause of its presence in short takeoff and vertical landing (STOVL)aircraft during hover as well as in other aerospace-related and industrial applications. Theexperimental measurementsinclude e ow visualization, surface-pressuredistributions,and velocitye elddataobtained using particleimagevelocimetry (PIV).Theexperimentaldata,especially the velocity e eld measurements, were used to verify theaccuracy of computational predictions. Computational results obtained using two differentturbulencemodels produced almost identical results. Comparisons with experimental results reveal that both models capture the signie cant features of this complex e ow and were in remarkably good agreement with the experimental data for the primary test case. The experiments and computations both revealed the presence of the impingement zone stagnation bubble, which contains low velocity recirculating e ow. Other features, including the complex shock structure and the high-speed radial wall jet, were also found to be very similar. The ability to measure and predictaccurately theimpinging jetbehavior, especially neartheground plane, is critical because these are regions with very high mean shear, thermal loads, and unsteady pressure forces, which contribute directly to the problem of ground erosion in STOVL applications.

Numerical and experimental study of a plasma cutting torch

Abstract: A low current intensity study of a cutting plasma torch is presented. The operating gas is oxygen discharging in an air environment. A two-dimensional turbulent plasma model is developed with the commercial code Fluent 4.5. An experimental and a theoretical study are presented. Two configurations were used: one where the arc is transferred to a rotating anode 19 mm away and the other in a real cutting configuration (distance nozzle exit-workpiece around a few millimetres). In the first configuration, spectroscopic measurements are made and compared with the model. The supersonic plasma behaviour is shown with a Mach number of 1.5 at the nozzle exit. The turbulent effect on the mass fraction field is presented. It concerns the effects of turbulence on the presence of oxygen near the plate, and by a comparison of theoretical and experimental temperatures we conclude that the arc presents turbulent behaviour. In the second configuration, a power balance of the cutting process is presented above and in the thickness of the plate. The model shows that the most important contribution to the fusion process is due to convection, conduction and radiation terms.

Design of a Low-Boom Supersonic Business Jet Using Cokriging Approximation Models

Abstract: In this paper we study the ability of the Cokriging method to represent functions with multiple local minima and sharp discontinuities for use in the multidimensional design of a low-boom supersonic business jet wing-body-canard configuration. Cokriging approximation models are an extension of the original Kriging method which incorporate secondary information such as the values of the gradients of the function being approximated. Provided that gradient information is available through inexpensive algorithms such as the adjoint method, this approach greatly improves on the accuracy and efficiency of the original Kriging method for high-dimensional design problems. In order to construct Cokriging approximation models, an automated Euler and Navier-Stokes based method, QSP107, has been developed to provide accurate performance and boom data with very rapid turnaround. The resulting approximations are used with a simple gradient-based optimizer to improve a multi-objective cost function with large variations in the design space. Results of sample two-dimensional test problems, together with a 15-dimensional test case are presented and discussed. The Cokriging method is a viable alternative to quadratic response surface methods for preliminary design using a moderate number of design variables, particularly when the cost function being optimized is very nonlinear. Nomenclature β constant underlying global portion of Kriging model CD drag coefficient f constant vector used in Kriging model f c constant vector used in Cokriging model k number of design variables n s number of sample points r vector of correlation values for Kriging model rc vector of correlation values for Cokriging model R(.) correlation function for Kriging model R correlation matrix for Kriging model Rc correlation matrix for Cokriging model x scalar component of x x p vector denoting the p th location in the design space y(.) unknown function ˆ y(.) estimated model of y(.) vector of correlation parameters for Kriging model ˆ σ 2 estimated sample variance

Integrated and/or modular high-speed aircraft

Abstract: An integrated and modular high-speed aircraft (200) and method of design and manufacture. The aircraft (200) can have a supersonic or near-sonic cruise Mach number. In one embodiment, the aircraft (200) can include an aft body integrated with a delta wing (204) and a rearwardly-tapering fuselage (202) to define a smooth forward-to-rear area distribution. A propulsion system (206), including an engine (216), inlet (220), and exhaust nozzle (222) can be integrated into the aft body to be at least partially hidden behind the wing (204). In one embodiment, the entrance of the inlet can be positioned beneath the wing (204), and the exit of the nozzle (222) can be positioned at or above the wing (204). An S-shaped inlet duct (221) can deliver air to the aft-mounted integrated engine.

Advanced Algorithms for Design and Optimization of Quiet Supersonic Platforms

Abstract: This paper describes the work carried out within the Stanford University group as part of the DARPA-funded Quiet Supersonic Platform (QSP) project. The objective of our work was to develop advanced numerical methods to facilitate the analysis and design of low sonic boom aircraft. The focus of the boom reduction activities was placed on two main ideas: the shaping of the configuration and a multidisciplinary design approach to minimize its total empty weight. Accurate and efficient tools are needed to achieve these tasks. Our approach was meant to enhance the existing state-of-the-art which was developed in the 1970s and during the early stages of the High Speed Research (HSR) program. For that purpose, we designed tools that would ultimately become fully non-linear (in contrast with current design efforts based on linear theories of the 1970s). These tools are also able to account for important tradeoffs between boom reduction and aerodynamic perormance, as well as other disciplines. Because of the difficulty of the problem, the tools were designed to support a combination of gradient and non-gradient automatic optimization techniques. As a result of our efforts, rapid turnaround boom analysis and design methods were developed. These methods permit the investigation of radical configuration changes and their effect on the ground boom signature and the L/D ratio of the aircraft. We have also created an environment for the automatic nonlinear analysis of QSP configurations based on the multiblock flow solver FLO107-MB. In addition , we have extended the adjoint-based design method to treat remote sensitivities to near-field pressure signatures, allowing for a very large number of parameters to be used in modifications of the aircraft geometry. All tools were carefully validated against existing experimental data, other boom prediction programs, and with systematic mesh refinement studies.

Measures of intermittency in driven supersonic flows.

Abstract: Scaling exponents for structure functions of the velocity, density, and entropy are computed for driven supersonic flows for rms Mach numbers of order unity, with numerical simulations using the piecewise parabolic method algorithm on grids of up to 512(3) points. The driving is made up of either one or three orthogonal shear waves. In all cases studied, the compressible component of the velocity in the statistically steady regime is weaker than its solenoidal counterpart by roughly a factor of 6. Exponents for the longitudinal component of the velocity are comparable to what is found in the incompressible case and appear insensitive to the presence of numerous shocks. Scaling exponents of the transverse components of the velocity are comparable to those for the longitudinal component. Density and entropy structure functions display strong departures from linear scaling. Finally, the scaling of structure functions of the energy transfer is also given and compared with the Kolmogorov refined similarity hypothesis.

Microwave energy release regimes for drag reduction in supersonic flows

Abstract: Results of numeric simulation and experimental investigation of gas dynamic processes in non-stationary interaction of gas dynamic discontinuity created by MW discharge in front of a blunt body in supersonic flow are presented. Two types of energy deposition — quasi-static and explosive — are modeled. Interaction mechanism via vortex formation in a shock layer is very efficient. For this mechanism calculations found out the scaling laws of interaction intensity and efficiency of quasi-static discontinuity (density well) over it length, width, "depth" and Mach number. The movie with time step of several microseconds of discharge domain drift and interaction with the shock layer in a weak chemilummescent emission is obtained. The efficiency of EM energy concentration, it's coupling with gas and plasma and air heating is analyzed. Attaining of the discharge phase when thin channel is formed is beneficial both for deliberating of energy stored in vibrational degrees of freedom and for launching of flow structuring in shock layer followed by the efficient drag reduction.

Global Shock Waves¶for the Supersonic Flow Past a Perturbed Cone

Abstract: We prove the global existence of a shock wave for the stationary supersonic gas flow past an infinite curved and symmetric cone. The flow is governed by the potential equation, as well as the boundary conditions on the shock and the surface of the body. It is shown that the solution to this problem exists globally in the whole space with a pointed shock attached at the tip of the cone and tends to a self-similar solution under some suitable conditions. Our analysis is based on a global uniform weighted energy estimate for the linearized problem. Combining this with the local existence result of Chen–Li [1] we establish the global existence and decay rate of the solution to the nonlinear problem.

Numerical Simulation of Real-Gas Flow in a Supersonic Turbine Nozzle Ring

Abstract: In small Rankine cycle power plants, it is advantageous to use organic media as the working fluid. A low-cost single-stage turbine design together with the high molecular weight of the fluid leads to high Mach numbers in the turbine. Turbine efficiency can be improved significantly by using an iterative design procedure based on an accurate CFD simulation of the flow. For this purpose, an existing Navier-Stokes solver is tailored for real gas, because the expansion of an organic fluid cannot be described with ideal gas equations. The proposed simulation method is applied for the calculation of supersonic flow in a turbine stator. The main contribution of the paper is to demonstrate how a typical ideal-gas CFD code can be adapted for real gases in a very general, fast, and robust manner.

Highly Expanded Flashing Liquid Jets

Abstract: Results arepresented of experiments with highly expanded e ashing liquid jets along with a one-dimensional numericalmodel.Theexperimentswerecarriedoutwithliquidiso-octanejetsissuing from asmallconical convergent nozzle into a low-pressure chamber. Images of the expanding jet off the nozzle exit section were obtained from a schlieren setup using a charge-coupled device camera. Analyses of these images enabled a qualitative visualization of the e ashing jet structure and geometry. At very low backpressures, it has been observed that the emerging jet wasformedbya central liquid core,and thephasechangeprocessoccurred onthesurfaceofthatliquidcore,giving rise to a sonic two-phase e ow. In addition, it is also inferred that the freshly formed two-phase e ow proceeded further to higher velocities and Mach numbers to terminate eventually with a complex shock wave structure to adjust pressures, as usual. A one-dimensional numerical analysis is carried out. The sudden phase change in the metastable liquid jet surface is modeled as an evaporation wave, for which the jump equations are solved. Next, the supersonic expansion of the two-phase mixture downstream of the evaporation wave is analyzed in a radial direction. Theone-dimensional calculation yielded theradial position of the shock wavelocation. It has been found that the numerical results are consistent with the experimental data.

Supersonic/Hypersonic Flutter and Postflutter of Geometrically Imperfect Circular Cylindrical Panels

Abstract: A theoretical investigation of the flutter and postflutter of infinitely long thin-walled circular cylindrical panels in a supersonic/hypersonic flowfield is presented. In this context, third-order piston theory and shockwave aerodynamics are used in conjunction with the geometrically nonlinear shell theory to obtain the pertinent aeroelastic governing equations. The effects of in-plane edge restraints and small initial geometric imperfections are also considered in the model. The objective is twofold: 1) to analyze the implications of nonlinear unsteady aerodynamics and structural nonlinearities on the character of the flutter instability boundary and 2) to outline the effects played, in the same respect, by a number of important geometrical, physical, and aerodynamic parameters characterizing the aeroelastic system. As a by-product of this analysis, the implications of these parameters on the linearized flutter instability behavior of the system are captured and emphasized. The behavior of the aeroelastic system in the vicinity of the flutter boundary is studied via the use of an encompassing methodology based on the Lyapunov first quantity. Numerical illustrations, supplying pertinent information on the implications of geometric and aerodynamic nonlinearities, as well as of other effects, such as curvature and thickness ratios, on the flutter instability and on the character of the flutter boundary are examined, and pertinent conclusions are outlined.

Particle Image Velocimetry in Mach 3.5 and 4.5 Shock-Tunnel Flows

Abstract: For the e rst time, a particle image velocimetry (PIV) system was used to study high-Mach-number e ows in a shock-tunnel facility with velocities of more than 1.5 km/s and measuring times in the millisecond range. An application of PIV to such a transient high-speed e ow is considerably more dife cult than to a continuous e ow because no online adjustments of the optics and the particle seeding can be done. Additionally, a proper seeding and timingofthefacility iscrucial.Firstwewilldiscussthemeasured velocity e eldbehind acontoured Lavalnozzle (design Mach number4.5 ). The measurement data show that thee owe eld at the nozzleexit is parallel to the nozzle axis and homogeneous as expected from supersonic nozzle theory. The average measured velocity corresponds very well to the calculated e ow velocity. The results are compared to measurements made with a conical Mach 3.5 nozzle that exhibits a diverging e owe eld. A wedge was further introduced into the parallel Mach 4.5 nozzle e ow to study the seed particle performance downstream of an oblique shock. The measured results are also in good agreement with calculated velocities from oblique shock theory. PIV has, therefore, proven to be an efe cient measurement method for high-speed and short-duration simulation facilities.

Ultra-fast-framing schlieren system for studies of the time evolution of jets in supersonic crossflows

Abstract: A new ultra-fast camera system is used to study the time evolution of jets in supersonic crossflows via schlieren imaging. The commercial high-speed camera includes eight independent intensified charged couple devices (ICCDs) and is capable of acquiring images at rates up to 100 MHz. A long-duration (up to 200 µs) xenon flashlamp is used as the continuous light source. The exposure times of the ICCDs and the interframing times were designed to achieve schlieren images with high spatial and temporal resolution. Example data are presented for a hydrogen jet injected into a high total enthalpy supersonic crossflow, generated using a short-duration impulse facility (expansion tube). The large-eddy convection characteristics of the jet, its penetration and the unsteady nature of the shock wave around it are analyzed. Temporal correlations, such as the movement of organized (coherent) structures and fluctuations in the bow-shock, are readily perceived by assembling the eight consecutive images as a movie (http://navier.stanford.edu/hanson/propulsion/scramjet/movies/t1179.html).