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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Progress in Validation of Wind-US for Ramjet/Scramjet Combustion

Validation of the Wind-US flow solver against two sets of experimental data involving high-speed combustion is attempted. First, the well-known Burrows- Kurkov supersonic hydrogen-air combustion test case is simulated, and the sensitively of ignition location and combustion performance to key parameters is explored. Second, a numerical model is developed for simulation of an X-43B candidate, full-scale, JP-7-fueled, internal flowpath operating in ramjet mode. Numerical results using an ethylene-air chemical kinetics model are directly compared against previously existing pressure-distribution data along the entire flowpath, obtained in direct-connect testing conducted at NASA Langley Research Center. Comparison to derived quantities such as burn efficiency and thermal throat location are also made. Reasonable to excellent agreement with experimental data is demonstrated for key parameters in both simulation efforts. Additional Wind-US feature needed to improve simulation efforts are described herein, including maintaining stagnation conditions at inflow boundaries for multi-species flow. An open issue regarding the sensitivity of isolator unstart to key model parameters is briefly discussed.

Engblom, William A.↗
NASA NTRS2006

Measurements and Theoretical Calculations of N2-broadening and N2-shift Coefficients in the v2 band of CH3D

In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the v2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm(exp -1) resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH3D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N2 pressure- broadening coefficients of 368 v2 transitions with quantum numbers as high as J"= 20 and K = 16, where K" = K' equivalent to K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported N2-induced pressure-shift coefficients vary from about 0.0003 to 0.0094 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J", and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J", J", and J" + 1 in the (sup Q)P-, (sup Q)Q-, and (sup Q)R-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressureshift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N2-pressure shifts whose vibrational contribution is derived from parameters fitted in the (sup Q)Q-branch of self-induced shifts of CH3D, are also in reasonable agreement with the scattered experimental data (20% in most cases).

Predoi-Cross, A.↗
NASA NTRSDate not supplied

Simulating Underexpanded Jets in Martian and Lunar Environments

As part of the Game Changing Development (GCD) Program, funded by NASA’s Space Technology Mission Directorate (STMD), the development of simulation capability for the prediction of extra-terrestrial Plume Surface Interaction (PSI) environments has been undertaken by the Fluid Dynamics Branch at NASA/MSFC. The GCD PSI Project, planned to be accomplished over a four year period, contains a Predictive Simulation Capability (PSC) Element focused on creating simulation capability for the reliable and accurate prediction of PSI in Martian (~650 Pa) and Lunar (vacuum) ambient environments. In addition to the PSC Element, the PSI Project also contains a companion Ground Testing Element for development of focused datasets for validation of predictive capability as well as a Flight-focused Instrumentation Element. This paper describes the activities and accomplishments in the past year for the Prediction of Plume Flow in low pressure environments component of the PSI Project. While the Loci/Chem Computational fluid dynamics (CFD) application has been validated and used extensively for simulating launch environments in atmospheric conditions, use of this tool for simulating supersonic plumes at Mars-like ambient pressure requires further validation. CFD simulations of underexpanded jets have been performed using Loci/Chem for Mars-like conditions to predict several metrics for steady laminar, turbulent, and impinging plumes. The CFD results are compared with an experimental data set for low Reynolds number plumes at these conditions in order to evaluate the current capability of the Loci/Chem tool for these types of environments. The CFD validation results to date show reasonable agreement with the experimental data across all of the metrics of interest for the configurations considered. The Loci/Chem-Boltzmann CFD application is a hybrid continuum/rarefied flow solver which extends modeling capabilities to very low pressure environments such as those on the Moon. The Loci/Chem-Boltzmann solver uses a gradient-based continuum breakdown criterion to restrict solution of the computationally expensive Boltzmann equation to only a subset of the domain, while using the Navier-Stokes equations elsewhere. This CFD application is under active development, and current efforts toward establishing production ready capability for evaluating Lunar plume surface interactions are well under way. Initial simulations of an Apollo LEM indicate that several regions of the flow require solving the Boltzmann equations due to extreme rarefaction. Early simulations are promising, indicating reasonable overall computational time for a full 3D human scale lander simulation.

Thomas Shurtz↗
NASA NTRS2022

Identification of Best Practices for Predicting Inlet Performance Using FUN3D Part 2: Installed Inlets.

A series of studies were performed to assess the impacts of boundary condition type and placement, grid refinement, and modeling parameters such as turbulence model and flux limiter on the predicted inlet performance for installed inlet configurations using the FUN3D flow solver. Two configurations were considered for the study; a wall-mounted Boundary Layer Ingestion (BLI) inlet and the C607 propulsion model tested in the 8x6 Supersonic Wind Tunnel at the NASA Glenn Research Center. The results of the studies were to be used to recommend best practices, as well as to assess the accuracy of FUN3D for inlet predictions. The results of BLI inlet stud-ies showed a minimal impact of grid refinement on the predicted inlet performance for a constant mass flow rate through the inlet. For the C607 propulsion model, the results showed that while the FUN3D predictions at the Aerodynamic Inter-face Plane (AIP) qualitatively agree with the experimental data, FUN3D showed a tendency to overpredict the circumferential distortion metric (IDCmax) and un-derpredict both the radial distortion metric (IDRmax) and the pressure recovery at the AIP (PRAIP ), with the differences between FUN3D and the experimental data increasing with increasing grid refinement and Mach number. Additionally, the outflow boundary location studies performed for both geometries showed that the solution at the AIP was not significantly impacted by the outflow boundary location as long as it was not placed at the location of the AIP. The modeling parameter studies did not indicate a path forward for improved predictions for either inlet con-figuration. Finally, comparisons between the mass flow plug and outflow geometry versions of the C607 propulsion model illustrated favorable agreement, which indi-cates that the differences observed are not caused by the outflow boundary model for this problem. This problem poses significant challenges to Reynolds-averaged Navier-Stokes (RANS) solvers due to the presence of shocks and flow separation in the inlet.

FUN3D↗
NASA NTRSDate not supplied

Simulating Underexpanded Plumes in Martian and Lunar Environments

While the Loci/Chem Computational fluid dynamics (CFD) application has been validated and used extensively for simulating launch environments in atmospheric conditions, use of this tool for simulating supersonic plumes at much lower ambient pressure requires further validation. Simulations of underexpanded plumes have been performed using Loci/Chem at Martian pressure to predict several metrics for laminar, turbulent, and impinging plumes. The CFD results are compared with an experimental data set for low Reynolds number plumes at these conditions in order to evaluate the current capability of the Loci/Chem tool for these types of environments. The CFD validation results to date show reasonable agreement with the experimental data across all the metrics of interest for the configurations considered. The Loci/Chem-Boltzmann tool is a hybrid continuum/rarefied flow solver which extends modeling capabilities to very low-pressure environments such as those on the Moon. The Loci/Chem-Boltzmann solver uses a gradient-based continuum breakdown criterion to restrict solution of the computationally expensive Boltzmann equation to only a subset of the domain, while using the Navier-Stokes equations elsewhere. This CFD application is under active development, and current efforts toward establishing production ready capability for evaluating Lunar plume surface interactions are well under way. Initial simulations of an Apollo Lunar excursion module indicate that several regions of the flow require solving the Boltzmann equations due to extreme rarefaction. Early simulations are promising, indicating reasonable overall computational time for a full 3D human scale lander simulation.

Plume Surface Interaction↗
NASA NTRS2001

Baseline Validation of Unstructured Grid Reynolds-Averaged Navier-Stokes Toward Flow Control

The value of the use of the Reynolds-averaged Navier-Stokes methodology for active flow control applications is assessed. An experimental flow control database exists for a NACA0015 airfoil modified at the leading edge to implement a fluidic actuator; hence, this configuration is used. Computational results are documented for the baseline wing configuration (no control) with the experimental results and assumes two-dimensional flow. The baseline wing configuration has discontinuities at the leading edge, trailing edge, and aft of midchord on the upper surface. A limited number of active flow control applications have been tested in the laboratory and in flight. These applications include dynamic stall control using a deformable leading edge, separation control for takeoff and landing flight conditions using piezoelectric devices, pulsed vortex generators, zero-net-mass oscillations, and thrust vectoring with zero-net-mass piezoelectric-driven oscillatory actuation. As yet, there is no definitive comparison with experimental data that indicates current computational capabilities can quantitatively predict the large aerodynamic performance gains achieved with active flow control in the laboratory. However, one study using the Reynolds-averaged Navier-Stokes (RANS) methodology has shown good quantitative agreement with experimental results for an isolated zero-net-mass actuator. In addition, some recent studies have used RANS to demonstrate qualitative performance gains compared with the experimental data for separation control on an airfoil. Those quantitative comparisons for both baseline and flow control cases indicated that computational results were in poor quantitative agreement with the experiments. The current research thrust will investigate the potential use of an unstructured grid RANS approach to predict aerodynamic performance for active flow control applications building on the early studies. First the computational results must quantitatively match experiments for the no-control case before proceeding to the time-dependent flow control case. This paper documents the baseline (no-control) case using an unswept airfoil configuration. The next section describes the configurations used for the computations and the experimentals. The computational approach is then described followed by results and concluding remarks.

Joslin, Ronald D.↗
NASA NTRS2013

The Paradox of a Wet (High H2O) and Dry (Low H2O/Ce) Mantle: High Water Concentrations in Mantle Garnet Pyroxenites from Hawaii

Water dissolved as trace amounts in anhydrous minerals has a large influence on the melting behavior and physical properties of the mantle. The water concentration of the oceanic mantle is inferred from the analyses of Mid-Ocean Ridge Basalt (MORB) and Oceanic Island Basalt (OIB). but there is little data from actual mantle samples. Moreover, enriched mineralogies (pyroxenites, eclogites) are thought as important sources of heterogeneity in the mantle, but their water concentrations and their effect on the water budget and cycling in the mantle are virtually unknown. Here, we analyzed by FTIR water in garnet clinopyroxenite xenoliths from Salt Lake Crater, Oahu, Hawaii. These pyroxenites are high-pressure (>20kb) crystal fractionates from alkalic melts. The clinopyroxenes (cpx) have 260 to 576 ppm wt H2O, with the least differentiated samples (Mg#>0.8) in the 400-500 ppm range. Orthopyroxene (opx) contain 117-265 ppm H2O, about half of that of cpx, consistent with other natural sample studies, but lower than cpx/opx equilibrium from experimental data. The pyroxenite cpx and opx H2O concentrations are at the high-end of on-and off-craton peridotite xenolith concentrations and those of Hawaiian spinel peridotites. In contrast, garnet has extremely low water contents (<5ppm H2O). There is no correlation between H2O in cpx and lithophile element concentrations. Phlogopite is present in some samples, and its modal abundance shows a positive correlation in Mg# with cpx, implying equilibrium. However, there is no correlation between H2O concentrations and or the presence of phlogopite. These data imply that cpx and opx may be at water saturation, far lower than experimental data suggest. Reconstructed bulk rock pyroxenite H2O ranges from 200-460 ppm (average 331 +/- 75 ppm), 2 to 8 times higher than H2O estimates for the MORB source (50-200 ppm), but in the range of E-MORB, OIB and the source of rejuvenated Hawaiian magmas. The average bulk rock pyroxenite H2O/Ce is 69 +/-35, lower than estimates of the MORB source (approx 150) or FOZO, C (200-250) mantle component, but consistent with "dry" EM sources (<100). These data suggest that a metasomatized, refertilized oceanic lithosphere that contains pyroxenitic veins (e.g. the lower part of an oceanic plate, where ascending melts can become trapped and crystallize), will have both higher water concentrations and low H2O/Ce, and may contribute to EM-type OIB sources, like that of Samoa basalts. Therefore, a low H2O/Ce mantle source may not necessarily be "dry".

Peslier, Anne H.↗
NASA NTRS1987

Three-dimensional nearfield characterization of a VSTOL jet in turbulent crossflow

This paper documents the measurement and prediction of the near-field evolution of the steady, subsonic, turbulent three-dimensional external aerodynamic flow-field associated with a high speed jet issued from an orifice perpendicular to an imposed crossflow velocity field. A parabolic Navier-Stokes CFD solver is employed, utilizing a Kappa-epsilon closure system with algebraic Reynolds stress equation, in concert with suitably defined porous far-field boundary conditions and a virtual source initial condition procedure. The CFD results correlate well with NASA generated near-field LDA experimental data on mean velocity and rms fluctuation velocity (interpolated to turbulent kinetic energy) distributions. The numerical results in the farther field predict the vortex roll-up and jet deflection/entrainment characterization verified by pitot-static mean velocity experimental data. Detailed results are presented for a circular jet for velocity ratios ranging 4 to 8.

Baker, A. J.↗
NASA NTRS1987

Turbulence statistics in fully developed channel flow at low Reynolds number

A direct numerical simulation of a turbulent channel flow is performed. The unsteady Navier-Stokes equations are solved numerically at a Reynolds number of 3300, based on the mean centerline velocity and channel half-width, with about 4 million grid points. All essential turbulence scales are resolved on the computational grid and no subgrid model is used. A large number of turbulence statistics are computed and compared with the existing experimental data at comparable Reynolds numbers. Agreements as well as discrepancies are discussed in detail. Particular attention is given to the behavior of turbulence correlations near the wall. A number of statistical correlations which are complementary to the existing experimental data are reported for the first time.

Kim, John↗
NASA NTRS1987

Experimental aerothermodynamic research of hypersonic aircraft

The 2-D and 3-D advance computer codes being developed for use in the design of such hypersonic aircraft as the National Aero-Space Plane require comparison of the computational results with a broad spectrum of experimental data to fully assess the validity of the codes. This is particularly true for complex flow fields with control surfaces present and for flows with separation, such as leeside flow. Therefore, the objective is to provide a hypersonic experimental data base required for validation of advanced computational fluid dynamics (CFD) computer codes and for development of more thorough understanding of the flow physics necessary for these codes. This is being done by implementing a comprehensive test program for a generic all-body hypersonic aircraft model in the NASA/Ames 3.5 foot Hypersonic Wind Tunnel over a broad range of test conditions to obtain pertinent surface and flowfield data. Results from the flow visualization portion of the investigation are presented.

Cleary, Joseph W.↗
NASA NTRS1987

Aeroelastic stability of bearingless rotors in forward flight

The finite element method was used to determine the dynamic stability of bearingless rotor blades (BR) in forward flight. The analysis was applied to four different BR configurations and the results were correlated with experimental data. The analysis was correlated with hover lag mode stability data for a simple three-blade BR rotor tested in various pitch link configurations. In addition, a more advanced BR which includes precone, blade twist, blade sweep, and a lag shear restraint is analyzed and compared to experimental data in both hover and forward flight.

Dull, Andrew L.↗
NASA NTRS2000

Experimental and Numerical Characterization of a Cylindrical Blackbody Cavity

During hypersonic flight, high temperatures and high heat fluxes are generated on the surfaces of vehicles. The Flight Loads Laboratory (FLL) at Dryden Flight Research Center (DFRC) is equipped with a calibration furnace, capable of calibrating heat flux gages up to 1100kW per square meters, and temperature sensors up to 2600 C. One heating configuration of the calibration furnace is a cylindrical blackbody cavity. Throughout the blackbody there are temperature gradients due to various boundary conditions. These boundary conditions include resistance heating, radiant heat transfer, and conduction to water-cooled electrodes. Also, an inert gas is purged through the graphite blackbody to prevent it from oxidizing. Consequently, the various modes of heat transfer present during operation of the blackbody cavity must be well understood in order to produce accurate heat flux gage and temperature sensor calibrations for use in ground testing or flight testing of hypersonic vehicles. The first step towards understanding the heat transfer in the blackbody cavity was to perform experiments at 1100 C, with and without outer surface insulation, while taking detailed temperature measurements inside the blackbody cavity. Steady state thermal models of the blackbody cavity were then developed. These models included detailed thermal analysis using commercial thermal analysis software. Conduction, radiation, and convection were considered in the thermal models for two cases: one with the outside of the blackbody cavity insulated and the second without insulation. This paper describes the experimental and numerical efforts used to characterize the steady state operation of the blackbody cavity. It describes the analysis of the test measurements, the boundary conditions used in the numerical models, and how the models were calibrated to fit the experimental data. Effects of various uncertainties, such as material properties, and convection are discussed.Initial thermal models predicted temperatures in the deepest part of the blackbody cavity within 7 C of the measured value and produced trends comparable to the experimental data, throughout the models. Adjustment of the boundary conditions, which were included in the thermal models, produced good agreement with measured temperatures. Free and forced convection of the purge gas inside the blackbody was found to be insignificant.

Abdelmessih, Amanie N.↗
NASA NTRS2014

USM3D Predictions of Supersonic Nozzle Flow

This study focused on the NASA Tetrahedral Unstructured Software System CFD code (USM3D) capability to predict supersonic plume flow. Previous studies, published in 2004 and 2009, investigated USM3D's results versus historical experimental data. This current study continued that comparison however focusing on the use of the volume souring to capture the shear layers and internal shock structure of the plume. This study was conducted using two benchmark axisymmetric supersonic jet experimental data sets. The study showed that with the use of volume sourcing, USM3D was able to capture and model a jet plume's shear layer and internal shock structure.

Carter, Melissa B.↗
NASA NTRS1973

Experimental and data analysis techniques for deducing collision-induced forces from photographic histories of engine rotor fragment impact/interaction with a containment ring

An analysis method termed TEJ-JET is described whereby measured transient elastic and inelastic deformations of an engine-rotor fragment-impacted structural ring are analyzed to deduce the transient external forces experienced by that ring as a result of fragment impact and interaction with the ring. Although the theoretical feasibility of the TEJ-JET concept was established, its practical feasibility when utilizing experimental measurements of limited precision and accuracy remains to be established. The experimental equipment and the techniques (high-speed motion photography) employed to measure the transient deformations of fragment-impacted rings are described. Sources of error and data uncertainties are identified. Techniques employed to reduce data reading uncertainties and to correct the data for optical-distortion effects are discussed. These procedures, including spatial smoothing of the deformed ring shape by Fourier series and timewise smoothing by Gram polynomials, are applied illustratively to recent measurements involving the impact of a single T58 turbine rotor blade against an aluminum containment ring. Plausible predictions of the fragment-ring impact/interaction forces are obtained by one branch of this TEJ-JET method; however, a second branch of this method, which provides an independent estimate of these forces, remains to be evaluated.

Yeghiayan, R. P.↗
NASA NTRS1951

Analysis of turbulent free-convection boundary layer on flat plate

With the use of Karman's integrated momentum equation for the boundary layer and data on the wall-shearing stress and heat transfer in forced-convection flow, a calculation was carried out for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. The calculation is for a fluid with a Prandtl number that is close to 1. A formula was derived for the heat-transfer coefficient that was in good agreement with experimental data in the range of Grashof numbers from 10sup10 to 10sup12. Because of the good agreement between the theoretical formula and the experimental data, the formula may be used to obtain data for high Grashof numbers. The calculation also yielded formulas for the maximum velocity in the boundary layer and for boundary-layer thickness.

Eckert, E R G↗
NASA NTRS1973

Multiple pure tone noise generation and control.

The generation of multiple pure tones in supersonic fans is discussed. The theoretical results of Kurasaka are reviewed and compared with experimental data obtained on a 36-in. diameter, 1550 ft/sec, 1.6 pressure ratio fan. Detailed measurements on bow shock locations taken with pressure transducers indicate that blade to blade discrepancies are the source of MPT generation. The paper presents some experimental results on an attempt to reduce the shock strength, and subsequently the MPT's, through blade modifications. Other attempts at reducing the MPT's through wall treatment, high inlet flow Mach number, acoustically treated splitters - are discussed. Experimental data is presented on the validity of these noise reduction methods.

Benzakein, M. J.↗
NASA NTRS1986

Temperature dependence of association of diatomic ions in diatomic gases

The present study compares the experimental rate coefficient temperature dependences for the association of diatomic ions in diatomic gases with the results of model calculations in which it is assumed that the stabilization of the initially formed unstable association complex occurs through the formation of a 'supercomplex'. The acceptable degree of agreement obtained between model and experimental data for the cases of four sample reactions, on the basis of a minimum of plausible assumptions, indicates that earlier theoretical models furnishing an accurate description of the formation and destruction of the association complex, but failing to reproduce experimental data, inadequately treated the temperature dependence of the stabilization step.

Johnsen, R.↗
NASA NTRS1991

Lateral tunneling through voltage-controlled barriers

The paper reports on a detailed experimental investigation of lateral tunneling between electrodes of a two-dimensional electron gas separated by the voltage-controlled barrier of a nanometer Schottky gate. The experimental data are modeled using the WKB method to calculate the tunneling probability of electrons through a barrier whose shape is determined from a solution of the two-dimensional Poisson equation. This model is in excellent agreement with the experimental data over a two order of magnitude range of current.

Manion, S. J.↗