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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Sensitivity of Middle Atmospheric Temperature and Circulation in the UIUC Mesosphere-Stratosphere-Troposphere GCM to the Treatment of Subgrid-Scale Gravity-Wave Breaking

The sensitivity of the middle atmospheric temperature and circulation to the treatment of mean- flow forcing due to breaking gravity waves was investigated using the University of Illinois at Urbana-Champaign 40-layer Mesosphere-Stratosphere-Troposphere General Circulation Model (MST-GCM). Three GCM experiments were performed. The gravity-wave forcing was represented first by Rayleigh friction, and then by the Alexander and Dunkerton (AD) parameterization with weak and strong breaking effects of gravity waves. In all experiments, the Palmer et al. parameterization was included to treat the breaking of topographic gravity waves in the troposphere and lower stratosphere. Overall, the experiment with the strong breaking effect simulates best the middle atmospheric temperature and circulation. With Rayleigh friction and the weak breaking effect, a large warm bias of up to 60 C was found in the summer upper mesosphere and lower thermosphere. This warm bias was linked to the inability of the GCM to simulate the reversal of the zonal winds from easterly to westerly crossing the mesopause in the summer hemisphere. With the strong breaking effect, the GCM was able to simulate this reversal, and essentially eliminated the warm bias. This improvement was the result of a much stronger meridional transport circulation that possesses a strong vertical ascending branch in the summer upper mesosphere, and hence large adiabatic cooling. Budget analysis indicates that 'in the middle atmosphere the forces that act to maintain a steady zonal-mean zonal wind are primarily those associated with the meridional transport circulation and breaking gravity waves. Contributions from the interaction of the model-resolved eddies with the mean flow are small. To obtain a transport circulation in the mesosphere of the UIUC MST-GCM that is strong enough to produce the observed cold summer mesopause, gravity-wave forcing larger than 100 m/s/day in magnitude is required near the summer mesopause. In the tropics, only with the AD parameterization can the model produce realistic semiannual oscillations.

Yang, Fanglin↗
NASA NTRS1988

Star-forming instabilities of a decelerating plane-parallel slab of finite thickness

In order to study how supernova blast waves might catalyze star formation, the stability of a slab of decelerating gas of finite thickness is explored. Previous analyses are extended by applying shock-like boundary conditions to the leading edge of the slab and by studying the effects of arbitrary deceleration. Contrary to some earlier claims, it is found that blast waves can indeed accelerate the rate of star formation in the interstellar medium by compressing the interstellar gas and enabling it to cool. Also, it is demonstrated that in an incompressible fluid, the symmetric and antisymmetric modes in the case of zero acceleration transform continuously into Rayleigh-Taylor and gravity-wave modes as acceleration grows more important. The dynamical overstability of an isothermal shock wave and its implications for star formation are discussed.

Voit, G. Mark↗
NASA NTRSDate not supplied

The NASA Ames Mars Global Climate Model: Benchmarking Publicly Released Source Code and Model Output

We have recently publicly released source code from the new NASA Ames Mars Global Climate Model (MGCM), which is based on NOAA/GFDL cubed-sphere finite volume (FV3-based) dynamical core (https://github.com/nasa/AmesGCM). We also we have a manuscript in preparation that aims to document the status of the new MGCM, and present selected simulations generated from it with interpretations and comparisons to both observations and the Ames Legacy MGCM. Output from our reference simulation will be made publicly available as well. One of our ongoing goals is to understand the underlying causes for differences between results produced with the new FV3-based dynamical core compared to the Legacy C-grid dynamical core. While the thermal and dynamical fields predicted with the new and Legacy GCMs are broadly similar for much of the year, there are key differences at low resolution when no external drag is applied to the new MGCM. This is particularly clear during a seasonal window of ~100 degrees of Ls surrounding southern summer solstice, when the predicted northern hemisphere polar warming is significantly over-predicted in the new MGCM. When we apply Rayleigh drag throughout much of the tropics and sub-tropics to the new MGCM, the simulated zonal mean structure of the atmosphere is much more consistent with both MCS observations and Legacy MGCM simulations. We note that the Kling et al. (2023; this meeting) study demonstrates that the behavior that we see with Rayleigh drag here can be recovered with high resolution simulations (in the horizontal and in the vertical) or with parameterized orographic and non-orographic gravity waves at lower resolution. While this work is still in progress, our preliminary conclusion is that the new dynamical core is less dissipative than the Legacy dynamical core. At low to moderate resolution, users of the new MGCM will need to be careful to use some sort of external drag, either in the form of gravity wave drag parameterizations or the simpler Rayleigh drag.

Melinda April Kahre↗
NASA NTRS1987

Steady bimodal convection in a cylinder at large Prandtl numbers

Steady bimodal convection of an infinite Prandtl-number Boussinesq fluid in a cylinder is considered. An asymptotic analysis similar to the one used by Buell and Catton (1986) for axisymmetric convection yields a solvability condition that determines the radial wavenumber. The analysis is valid for convection far away from the origin, the lateral boundary, and any pattern dislocations. The azimuthal wave number is treated as a parameter, although in real systems it is dependent on the initial and boundary conditions. Results are presented for Rayleigh numbers between 14,000 and 60,000, and for azimuthal wave numbers between 5 and 7. It is shown that for increasing Rayleigh numbers, the selected radial wave number and the heat transfer tend to become independent of the azimuthal wave number. No quantitative experimental data are available, but one qualitative comparison is good.

Buell, Jeffrey C.↗
NASA NTRS1992

Penetrative convection - Parametrized expression for the growth rates

The equations determining the linear growth rate omega characterizing a convectively unstable fluid with Rayleigh number R(u) bounded below by an impenetrable free boundary and above by a convectively stable fluid with Rayleigh number R(s), are solved numerically. Using the analytical Rayleigh-Benard growth rate omega (RB) as a convenient functional form, it is possible to fit the numerical values for omega if the vertical wave number k(z) = n(pi) and the Rayleigh number R(RB) are taken to be functions of R(s), R(u), and the horizontal wave number k-perpendicular rather than n = integer as in the Rayleigh-Benard case. In addition, contrary to Rayleigh-Benard convection, in which the critical Rayleigh number is fixed, it is found that R super (cr) sub u is variable in the presence of a stable layer, (i.e., it depends on R(s)).

Savolainen, V.↗
NASA NTRS1990

Linear instability of the supersonic wake behind a flat plate aligned with a uniform stream

A theoretical and numerical study is presented of the growth of linear disturbances in the laminar compressible supersonic wake behind a flat plate aligned with a uniform stream. The approach adopted is that of classical linear stability theory and covers both two- and three-dimensional disturbances. The basic flow is described, and the linear stability problem is formulated that leads to the compressible Rayleigh equation. The stability of short-wave disturbances is then analyzed in the very near wake where the compressible analog of the Goldstein double structure provides an asymptotic description for the unperturbed flow. The behavior of long waves is then considered. The waves are not as long as the plate length but are long compared to the boundary-layer thickness. Numerical solutions of the Rayleigh equation are discussed. Numerical results are then presented for a range of streamwise stations, Mach numbers, and wave propagation angles.

Papageorgiou, D. T.↗
NASA NTRS1978

Infrared Astronomical Satellite (IRAS) analysis, appendix B

Analytical results derived during the development of the PADE program are presented. Near field on-axis diffraction from a circular aperture is analyzed by integrating Kirchhoff's formula, the boundary wave formulation, and the Rayleigh-Sommerfeld theory. Far field on-axis diffraction from obliquely illuminated apertures is described using the angular spectrum approach. Transmission functions and diffracted fields for rectangular, circular, and rotated square apertures are presented.

Source record↗
NASA NTRS1983

A non-Gaussian statistical model for surface elevation of nonlinear random wave fields

Probability density function of the surface elevation of a nonlinear random wave field is obtained. The wave model is based on the Stokes expansion carried to the third order for both deep water waves and waves in finite depth. The amplitude and phase of the first-order component of the Stokes wave are assumed to be Rayleigh and uniformly distributed and slowly varying, respectively. The probability density function for the deep water case was found to depend on two parameters: the root-mean-square surface elevation and the significant slope. For water of finite depth, an additional parameter, the nondimensional depth, is also required. An important difference between the present result and the Gram-Charlier representation is that the present probability density functions are always nonnegative. It is also found that the 'constant' term in the Stokes expansion, usually neglected in deterministic studies, plays an important role in determining the details of the density function. The results compare well with laboratory and field experiment data.

Huang, N. E.↗
NASA NTRS1992

Gallery of fluid motion

Winning photographs from the ninth Annual Fluid Mechanics Photo Contest held by the Division of Fluid Dynamics of the American Physical Society in November 1991 are displayed. Pictures are presented of vortex flows, a periodic axisymmetric vortex breakdown in a cylinder with a rotating end wall, impacting water drops, a vortex structure behind a disk started from rest, dynamic stall, blue waves, isotherms in turbulent Rayleigh-Benard convection, a square jet, 'vapor lines' emanating from water droplets, viscosity effects on the directional solidification of NH4Cl solution in a Hele-Shaw cell, and stationary cross-flow vortices.

Reed, Helen L.↗
NASA NTRS2022

Hybrid Kinetic Model of the Interaction Between the Dense Plasma Clouds and Magnetospheric Plasma on Large Time and Spatial Scales, and Comparison With MMS Observations

We present a new simulation results of the cloud dynamics in the ambient magnetospheric plasma on the large time and spatial scales. It was assumed that these impulsive structures observed by the MMS spacecraft originally were created because of the reconnection at the magnetopause. Our new 3-D hybrid kinetic modeling on the large time and spatial scales captures several of these processes: an excitation of the electromagnetic waves (whistler and shear-Alfvén waves) and plasma instabilities (mirror and flute); a formation of shock waves, and collapsing diamagnetic cavity; particle acceleration. A strong overshoot in plasma density profile was observed in the modeling and MMS observation at the interface between the cloud and magnetospheric plasma. The cloud expansion into ambient magnetospheric plasma causes the flute waves connected with excitation of the Rayleigh-Taylor instability observed at the overshoot in plasma density profile across the external magnetic field. The modeling demonstrates a formation of the whistler waves at the initial stage which propagate in the external magnetic field direction. At the later stage, a formation of shear-Alfvén waves was observed

A. S. Lipatov↗
NASA NTRS2005

Control of Combustion-Instabilities Through Various Passive Devices

It is well known that under some operating conditions, rocket engines (using solid or liquid fuels) exhibit unstable modes of operation that can lead to engine malfunction and shutdown. The sources of these instabilities are diverse and are dependent on fuel, chamber geometry and various upstream sources such as pumps, valves and injection mechanism. It is believed that combustion-acoustic instabilities occur when the acoustic energy increase due to the unsteady heat release of the flame is greater than the losses of acoustic energy from the system [1, 2]. Giammar and Putnam [3] performed a comprehensive study of noise generated by gasfired industrial burners and made several key observations; flow noise was sometimes more intense than combustion roar, which tended to have a characteristic frequency spectrum. Turbulence was amplified by the flame. The noise power varied directly with combustion intensity and also with the product of pressure drop and heat release rate. Karchmer [4] correlated the noise emitted from a turbofan jet engine with that in the combustion chamber. This is important, since it quantified how much of the noise from an engine originates in the combustor. A physical interpretation of the interchange of energy between sound waves and unsteady heat release rates was given by Rayleigh [5] for inviscid, linear perturbations. Bloxidge et al [6] extended Rayleigh s criterion to describe the interaction of unsteady combustion with one-dimensional acoustic waves in a duct. Solutions to the mass, momentum and energy conservation equations in the pre- and post-flame zones were matched by making several assumptions about the combustion process. They concluded that changes in boundary conditions affect the energy balance of acoustic waves in the combustor. Abouseif et al [7] also solved the one-dimensional flow equations, but they used a onestep reaction to evaluate the unsteady heat release rate by relating it to temperature and velocity perturbations. Their analysis showed that oscillations arise from coupling between entropy waves produced at the flame and pressure waves originating from the nozzle. Yang and Culick [8] assumed a thin flame sheet, which is distorted by velocity and pressure oscillations. Conservation equations were expressed in integral form and solutions for the acoustic wave equations and complex frequencies were obtained. The imaginary part of the frequency indicated stability regions of the flame. Activation energy asymptotics together with a one-step reaction were used by McIntosh [9] to study the effects of acoustic forcing and feedback on unsteady, one-dimensional flames. He found that the flame stability was altered by the upstream acoustic feedback. Shyy et al [10] used a high-accuracy TVD scheme to simulate unsteady, one-dimensional longitudinal, combustion instabilities. However, numerical diffusion was not completely eliminated. Recently, Prasad [11] investigated numerically the interactions of pressure perturbations with premixed flames. He used complex chemistry to study responses of pressure perturbations in one-dimensional combustors. His results indicated that reflected and transmitted waves differed significantly from incident waves.

Frendi, Kader↗
NASA NTRS1968

General remainder theorem.

Remainder theorem of Rayleigh-Schroedinger perturbation theory for calculating wave functions to higher order

Epstein, S. T.↗
NASA NTRS2018

Green's Function Applicable to Turbofan Exhaust Noise in Jets with an External Center-Body

The problem of propagation of sound across the shear layer in a turbofan jet exhaust with an external center-body is discussed. The wave equation of interest is compressible Rayleigh equation. Two forms of the equation are considered, and the Green's function solutions subject to appropriate surface conditions on the center-body and flight condition in the ambient are presented. Directivity studied in a heated exhaust at temperature ratio of 2.0 and Mach number 0.90 indicate that a rigid center-body tends to increase the sound propagation at forward angles relative to an exhaust without a center-body, while application of suitable surface liner may significantly reduce this enhancement. A general form of the far-field solution to the propagation equation in a parallel flow under supersonic conditions and in the neighborhood of the shear layer singularity is also discussed.

Noise↗
NASA NTRS1996

Local and Global Bifurcations of Flow Fields During Physical Vapor Transport: Application to a Microgravity Experiment

The local bifurcation of the flow field, during physical vapor transport for a parametric range of experimental interest, shows that its dynamical state ranges from steady to aperiodic. Comparison of computationally predicted velocity profiles with laser doppler velocimetry measurements shows reasonable agreement in both magnitude and planform. Correlation of experimentally measured crystal quality with the predicted dynamical state of the flow field shows a degradation of quality with an increase in Rayleigh number. The global bifurcation of the flow field corresponding to low crystal quality indicates the presence of a traveling wave for Ra = 1.09 x 10(exp 5). For this Rayleigh number threshold a chaotic transport state occurs. However, a microgravity environment for this case effectively stabilizes the flow to diffusive-advective and provides the setting to grow crystals with optimal quality.

Duval, W. M. B.↗
NASA NTRS1985

The effect of topography on the evolution of unstable disturbances in a baroclinic atmosphere

A two layer spectral quasi-geostrophic model is used to simulate the effects of topography on the equilibria, their stability, and the long term evolution of incipient unstable waves. The flow is forced by latitudinally dependent radiative heating. Dissipation is in the form of Rayleigh friction. An analytical solution is found for the propagating finite amplitude waves which result from baroclinic instability of the zonal winds when topography is absent. The appearance of this solution for wavelengths just longer than the Rossby radius of deformation and disappearance of ultra-long wavelengths is interpreted in terms of the Hopf bifurcation theory. Simple dynamic and thermodynamic criteria for the existence of periodic Rossby solutions are presented. A Floquet stability analysis shows that the waves are neutral. The nature of the form drag instability of high index equilibria is investigated. The proximity of the equilibrium shear to a resonant value is essential for the instability, provided the equilibrium occurs at a slightly stronger shear than resonance.

Clark, J. H. E.↗
NASA NTRS2018

Green's Function Applicable to Turbofan Exhaust Noise in Jets with an External Center-Body

The problem of propagation of sound across the shear layer in a turbofan jet exhaust with an external center-body is discussed. The wave equation of interest is the compressible Rayleigh equation. Two forms of the equation are considered, and the Green's function solutions, subject to appropriate surface conditions on the center-body and flight condition in the ambient, are presented. Directivity studies in a heated exhaust at temperature ratio of 2.0 and Mach number 0.90 indicate that a rigid center-body tends to increase the sound propagation at forward angles relative to an exhaust without a center-body, while application of suitable surface liner may significantly reduce this enhancement.

Noise↗
NASA NTRS1991

Monograph on propagation of sound waves in curved ducts

After reviewing and evaluating the existing material on sound propagation in curved ducts without flow, it seems strange that, except for Lord Rayleigh in 1878, no book on acoustics has treated the case of wave motion in bends. This monograph reviews the available analytical and experimental material, nearly 30 papers published on this subject so far, and concisely summarizes what has been learned about the motion of sound in hard-wall and acoustically lined cylindrical bends.

Rostafinski, Wojciech↗
NASA NTRS1972

The interaction of moderately strong shock waves with thick perforated walls of low porosity

A theoretical prediction is given of the flow through thick perforated walls of low porosity resulting from the impingement of a moderately strong traveling shock wave. The model was a flat plate positioned normal to the direction of the flow. Holes bored in the plate parallel to the direction of the flow provided nominal hole length-to-diameter ratios of 10:1 and an axial porosity of 25 percent of the flow channel cross section. The flow field behind the reflected shock wave was assumed to behave as a reservoir producing a quasi-steady duct flow through the model. Rayleigh and Fanno duct flow theoretical computations for each of three possible auxiliary wave patterns that can be associated with the transmitted shock (to satisfy contact surface compatibility) were used to provide bounding solutions as an alternative to the more complex influence coefficients method. Qualitative and quantitative behavior was verified in a 1.5- by 2.0-in. helium shock tube. High speed Schlieren photography, piezoelectric pressure-time histories, and electronic-counter wave speed measurements were used to assess the extent of correlation with the theoretical flow models. Reduced data indicated the adequacy of the bounding theory approach to predict wave phenomena and quantitative response.

Grant, D. J.↗