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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Plume and Shock Interaction Effects on Sonic Boom in the 1-foot by 1-foot Supersonic Wind Tunnel

The desire to reduce or eliminate the operational restrictions of supersonic aircraft over populated areas has led to extensive research at NASA. Restrictions are due to the disturbance of the sonic boom, caused by the coalescence of shock waves formed by the aircraft. A study has been performed focused on reducing the magnitude of the sonic boom N-wave generated by airplane components with a focus on shock waves caused by the exhaust nozzle plume. Testing was completed in the 1-foot by 1-foot supersonic wind tunnel to study the effects of an exhaust nozzle plume and shock wave interaction. The plume and shock interaction study was developed to collect data for computational fluid dynamics (CFD) validation of a nozzle plume passing through the shock generated from the wing or tail of a supersonic vehicle. The wing or tail was simulated with a wedgeshaped shock generator. This test entry was the first of two phases to collect schlieren images and off-body static pressure profiles. Three wedge configurations were tested consisting of strut-mounted wedges of 2.5- degrees and 5-degrees. Three propulsion configurations were tested simulating the propulsion pod and aft deck from a low boom vehicle concept, which also provided a trailing edge shock and plume interaction. Findings include how the interaction of the jet plume caused a thickening of the shock generated by the wedge (or aft deck) and demonstrate how the shock location moved with increasing nozzle pressure ratio.

Shock wave interaction↗
NASA NTRS1991

Guided waves in a multilayered composite and ultrasonic nondestructive evaluation

Analysis of wave propagation in a laminated composite plate with many layers is made difficult by the anisotropy of the laminae, different lay-ups, many layers and defects in the fabricated plate. A good understanding of the wave field in such a plate without defects is a prerequisite for use of ultrasonic techniques to evaluate the various defects that can substantially reduce the strength and service life of this structure. Results of modeling studies of wave propagation and scattering in a multilayered composite plate are presented. The analysis technique combines the finite element discretization through the thickness with wave form representation along the plate in order to calculate the dispersive modes of propagation in the plate. To study scattering of these waves by a matrix crack that grows into delaminations, a hybrid finite element representation of the field near the crack and the modal representation of the scattered exterior field are used. Results are presented showing the dependence of the reflection and transmission coefficients on the size of the crack with delamination which can be used to size the defect using ultrasonic techniques.

Datta, S. K.↗
NASA NTRS1974

Magnetic measurements in model experiments

Plasma parameters for modeling of the interaction between the solar wind and the earth's magnetic field are selected on the limited modeling principle (plasma velocity 3 x 10 to the 7th power cm/sec, density 10 to the 13th power cm/3, electron temperature approximately 15 eV). Measurements were made with magnetic probes capable of developing all 3 components inside the magnetic field. The resulting magnetic field charts indicate that a neutral layer forms on the night side in the model experiments. A magnetosphere free of plasma streams is established on the daytime side. A shock wave forms on the boundary of the magnetosphere, its width c/omega sub 0 in accordance with theory, where omega sub 0 is the total Langmuir width.

Dubinin, E. M.↗
NASA NTRS1975

Correlated electric and magnetic fields from lightning return strokes

The first broad band (1 kHz to 5 mHz) correlated measurements of electric and magnetic fields from close lightning return strokes are presented. Sample wave forms are shown for the distance range 2-200 km. The transmission line return stroke model is used to find a typical current wave shape and return stroke velocity from the experimental data, and theoretical curves are given of electric and magnetic field as a function of time for 1, 5, 10, and 100 km by using this typical current and velocity.

Uman, M. A.↗
NASA NTRS1978

Verification results for the Spectral Ocean Wave Model (SOWM) by means of significant wave height measurements made by the GEOS-3 spacecraft

Significant wave heights estimated from the shape of the return pulse wave form of the altimeter on GEOS-3 for forty-four orbit segments obtained during 1975 and 1976 are compared with the significant wave heights specified by the spectral ocean wave model (SOWM), which is the presently operational numerical wave forecasting model at the Fleet Numerical Weather Central. Except for a number of orbit segments with poor agreement and larger errors, the SOWM specifications tended to be biased from 0.5 to 1.0 meters too low and to have RMS errors of 1.0 to 1.4 meters. The much fewer larger errors can be attributed to poor wind data for some parts of the Northern Hemisphere oceans. The bias can be attributed to the somewhat too light winds used to generate the waves in the model. Other sources of error are identified in the equatorial and trade wind areas.

Pierson, W. J.↗
NASA NTRS1971

Diffraction of a plane wave by a three-dimensional corner

By the superposition of the conical solution for the diffraction of a plane pulse by a three dimensional corner, the solution for a general incident plane wave is constructed. A numerical program is presented for the computation of the pressure distribution on the surface due to an incident plane wave of any wave form and at any incident angle. Numerical examples are presented to show the pressure signature at several points on the surface due to incident wave with a front shock wave, two shock waves in succession, or a compression wave with same peak pressure. The examples show that when the distance of a point on the surface from the edges or the vertex is comparable to the distance for the front pressure raise to reach the maximum, the peak pressure at that point can be much less than that given by a regular reflection, because the diffracted wave front arrives at that point prior to the arrival of the peak incident wave.

Ting, L.↗
NASA NTRS1973

Time variation in the reaction-zone structure of two-phase spray detonations.

A detailed theoretical analysis of the time-varying detonation structure in a monodisperse spray is presented. The theory identifies experimentally observed reaction-zone overpressures as deriving from blast waves formed therein by the explosive ignition of the spray droplets, and follows in time the motion, change in strength, and interactions of these blast waves with one another, and with the leading shock. The results are compared with experimental data by modeling the motion of a finite-size circular pressure transducer through the theoretical data field in an x-t space.

Pierce, T. H.↗
NASA NTRS2000

Unsteady Analysis of Inlet-Compressor Acoustic Interactions Using Coupled 3-D and 1-D CFD Codes

It is well known that the dynamic response of a mixed compression supersonic inlet is very sensitive to the boundary condition imposed at the subsonic exit (engine face) of the inlet. In previous work, a 3-D computational fluid dynamics (CFD) inlet code (NPARC) was coupled at the engine face to a 3-D turbomachinery code (ADPAC) simulating an isolated rotor and the coupled simulation used to study the unsteady response of the inlet. The main problem with this approach is that the high fidelity turbomachinery simulation becomes prohibitively expensive as more stages are included in the simulation. In this paper, an alternative approach is explored, wherein the inlet code is coupled to a lesser fidelity 1-D transient compressor code (DYNTECC) which simulates the whole compressor. The specific application chosen for this evaluation is the collapsing bump experiment performed at the University of Cincinnati, wherein reflections of a large-amplitude acoustic pulse from a compressor were measured. The metrics for comparison are the pulse strength (time integral of the pulse amplitude) and wave form (shape). When the compressor is modeled by stage characteristics the computed strength is about ten percent greater than that for the experiment, but the wave shapes are in poor agreement. An alternate approach that uses a fixed rise in duct total pressure and temperature (so-called 'lossy' duct) to simulate a compressor gives good pulse shapes but the strength is about 30 percent low.

Suresh, A.↗
NASA NTRS1979

Geos 3 wave height measurements - An assessment during high sea state conditions in the North Atlantic

The sea state in the North Atlantic Ocean has been monitored in February, 1977 to obtain data for verification of Geos 3 radio altimeter wave form data. The altimeter sea state data were found to be in good agreement with in situ sea state measurements and with aircraft remote sensing measurements of wave height. The average difference between the supporting data and Geos 3 was 0.34 m, and the standard deviation 0.61 m. Contour maps of sea state constructed for large regions of the earth's oceans on the basis of Geos 3 altimeter measurements exhibited systematic differences from operationally available computerized maps. It is thought that the underestimation of significant wave height maxima in the operational maps and the underestimation of the speed of movement of oceanic cyclones may be due to basic errors in the output of atmospheric primitive-equation models. Because of the narrow swath width of the Geos-3 sensor, data from several satellite orbits must be combined to construct contour maps, leading to low values of significant wave heights.

Parsons, C. L.↗
NASA NTRS1991

Development of a grid-independent approximate Riemannsolver

A grid-independent approximate Riemann solver for use with the Euler and Navier-Stokes equations was introduced and explored. The two-dimensional Euler and Navier-Stokes equations are described in Cartesian and generalized coordinates, as well as the traveling wave form of the Euler equations. The spatial and temporal discretization are described for both explicit and implicit time-marching schemes. The grid-aligned flux function of Roe is outlined, while the 5-wave grid-independent flux function is derived. The stability and monotonicity analysis of the 5-wave model are presented. Two-dimensional results are provided and extended to three dimensions. The corresponding results are presented.

Rumsey, Christopher Lockwood↗
NASA NTRS1996

Spectra of Baroclinic Inertia-Gravity Wave Turbulence

Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea surface height oscillations. They also contribute to the kinetic energy of horizontal motions in the subsurface layer. Measured by the ratio of water particle velocity to wave phase speed, the wave nonlinearity may be rather high. Given a continuous supply of energy from external sources, nonlinear wave-wave interactions among IG waves would result in inertial cascades of energy, momentum, and wave action. Based on a recently developed theory of wave turbulence in scale-dependent systems, these cascades are investigated and IG wave spectra are derived for an arbitrary degree of wave nonlinearity. Comparisons with satellite-altimetry-based spectra of surface height variations and with energy spectra of horizontal velocity fluctuations show good agreement. The well-known spectral peak at the inertial frequency is thus explained as a result of the inverse cascade. Finally, we discuss a possibility of inferring the internal Rossby radius of deformation and other dynamical properties of the upper thermocline from the spectra of SSH (sea surface height) variations based on altimeter measurements.

Glazman, Roman E.↗
NASA NTRS1995

Gravity Waves Near 300 km Over the Polar Caps

Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.

Johnson, F. S.↗
NASA NTRS2010

Slot Nozzle Effects for Reduced Sonic Boom on a Generic Supersonic Wing Section

NASA has conducted research programs to reduce or eliminate the operational restrictions of supersonic aircraft over populated areas. Restrictions are due to the disturbance from the sonic boom, caused by the coalescence of shock waves formed off the aircraft. Results from two-dimensional computational fluid dynamic (CFD) analyses (performed on a baseline Mach 2.0 nozzle in a simulated Mach 2.2 flow) indicate that over-expanded and under-expanded operation of the nozzle has an effect on the N-wave boom signature. Analyses demonstrate the feasibility of reducing the magnitude of the sonic boom N-wave by controlling the nozzle plume interaction with the nozzle boat tail shock structure. This work was extended to study the impact of integrating a high aspect ratio exhaust nozzle or long slot nozzle on the trailing edge of a supersonic wing. The nozzle is operated in a highly under-expanded condition, creating a large exhaust plume and a shock at the trailing edge of the wing. This shock interacts with and suppresses the expansion wave caused by the wing, a major contributor to the sonic boom signature. The goal was to reduce the near field pressures caused by the expansion using a slot nozzle located at the wing trailing edge. Results from CFD analysis on a simulated wing cross-section and a slot nozzle indicate potential reductions in sonic boom signature compared to a baseline wing with no propulsion or trailing edge exhaust. Future studies could investigate if this effect could be useful on a supersonic aircraft for main propulsion, auxiliary propulsion, or flow control.

Castner, Raymond S.↗