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At least 379 records · Page 21

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NASA NTRS1988

Transient natural convection heat and mass transfer in a rectangular enclosure - A numerical analysis

A numerical analysis of transient heat and solute transport across a rectangular cavity with combined horizontal temperature and concentration gradients is performed by a numerical method based on the SIMPLE. Numerical results show that the average Nusselt and Sherwood numbers both decrease markedly when the solutal and thermal buoyancy forces act in the opposite directions. When the solutal and thermal buoyancy forces act in the same directions, however, the average Sherwood number increases significantly and yet the average Nusselt number decreases slightly.

Han, Samuel S.↗

NASA NTRS1988

Stress-intensity factors for corner cracks in rectangular bars

Stress intensity factors are presented for a wide range of quarter-elliptical corner cracks in a rectangular bar. The bars were subjected to remote tension, out-of-plane bending, or in-plane bending loading, and the stress intensity factors were calculated from a three-dimensional finite element analysis using the nodal-force method. For all loadings considered, smaller width bars produce higher normalized stress intensity factors than the larger width bars. For tensile loading, quarter-circular corner cracks give higher stress intensity factors near the free surfaces and lower values in the interior. The results are compared with data in the literature for remote tensile loading.

Raju, I. S.↗

NASA NTRS1989

Effect of simulated glaze ice on a rectangular wing

Experimental measurements of the effect of simulated glaze ice on a three-dimensional wing are presented. A semispan wing of effective aspect ratio five was mounted from a splitter plate in the OSU subsonic wind tunnel. The model has a straight, untwisted rectangular platform, and uses a NACA 0012 airfoil section. Surface pressures were measured at 5 semispan locations and a total-pressure wake-survey probe was used on the model centerline. The section lift and drag data from the model centerline compared well to earlier two-dimensional data. These data show a large drag and maximum lift penalty due to the simulated glaze ice. Three-dimensional span-load data compare well to computational results.

Bragg, M. B.↗

NASA NTRS1988

Eddy viscosity measurements in a rectangular jet

The flow field of a rectangular jet with a 2:1 aspect ratio was studied at a Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry (LDV). Velocity gradients, Reynolds stress tensor components, and scalar eddy viscosities are presented for the major and minor axis planes of the jet. The eddy viscosity model was found to be applicable only in the direction of maximum mean velocity gradient.

Swan, David H.↗

NASA NTRS1989

Asymptotic modal analysis of a rectangular acoustic cavity and characterization of its intensification zones

Asymptotic modal analysis (AMA) is used to study a rectangular cavity with a flexible vibrating portion on one wall and five rigid walls. The agreement between mean square pressure levels of the cavity interior calculated from classical modal analysis and from the AMA method improved as the number of responding modes increased. It is shown that intensification effects were due to both the excitation location and the response location.

Peretti, Linda F.↗

NASA NTRS1989

Supersonic rectangular jet impingement noise experiments

The discrete frequency sound produced by jets issuing from a convergent, rectangular nozzle of aspect ratio 4.24 was investigated. Experiments were performed both with the free jet and with the jet impinging on a hard ground surface. The impingement tones that dominate the impinging jet spectra show a definite staging behavior which appears to be biased toward the free jet screech frequency once the separation distance exceeds the region of substantial shock cell development. The frequency variation of the impingement tone stages fit the details of a feedback cycle if the disturbance convection velocity is chosen to be 20 percent higher than that necessary to satisfy the screech feedback loop. Phase locked optical records show a flapping mode of jet oscillation with tones at or near the screech frequency, with superimposed symmetric oscillations when a second dominant tone of unrelated frequency appears in the spectrum.

Norum, Thomas D.↗

NASA NTRS1989

Rectangular jets in a crossflow

Rectangular jets injected from a flat plate into a crossflow at large angles have been studied. Results were obtained as surface pressure distributions, mean velocity vector plots, turbulence intensities, and Reynolds stresses in the jet plume. The length-to-width ratio of the jets was 4, and the jets were aligned streamwise as single and side-by-side dual jets. The jet injection angles were 90 and 60 deg. Surface pressure distribution results were obtained for jet-to-freestream velocity ratios of 2.2, 4, and 8. Mean flow and turbulence flowfield data were obtained for the side-by-side dual jets, mainly for the jet-to-freestream velocity ratio of 4. The jets featured strong negative pressure peaks near the front nozzle corners. The 60-deg jets produced lower magnitude negative pressures, which are distributed over a lesser area when compared to the 90-deg jets.

Kavsaoglu, M. S.↗

NASA NTRS1988

Radiative transfer in rectangular enclosures - A discretized exchange factor solution

The discretized exchange factor method is used to analyze radiative exchange in a rectangular enclosure. The results compare excellently with those of other methods, especially the zonal method. Since the direct exchange factors are between nodal points no integration is necessary for evaluation of these factors. It is found that the present approach provides accurate results even when a small number of nodes is used.

Naraghi, M. H. N.↗

NASA NTRS1989

Rectangular subsonic jet flow field measurements

Flow field measurements are presented of 3 subsonic rectangular cold air jets. The 3 cases presented had aspect ratios of 1 x 2, 1 x 4 at a Mach number of 0.09 and an aspect ratio of 1 x 2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemoneter system. The presented data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data is presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made. All tabular data are available in ASCII format on MS-DOS compatible disks.

Morrison, Gerald L.↗

NASA NTRS1988

Laser velocimeter and total pressure measurements in circular-to-rectangular transition ducts

A comprehensive set of total pressure and three-component laser velocimetry (LV) data were obtained within two circular-to-rectangular transition ducts at low subsonic speeds. This set of reference data was acquired for use in identifying secondary flow mechanisms and for assessing the accuracy of computational procedures for calculating such flows. Data were obtained at the inlet and exit planes of an aspect ratio three duct having a length-to-diameter ratio of one (AR310) and an aspect ratio six duct having a length-to-diameter ratio of three (AR630). Each duct was unseparated throughout its transition section. It is therefore concluded that secondary flows can play an important part in the fluid dynamics of transition ducts and needs to be addressed in computational analysis. The strength of the secondary flows depends on both the aspect ratio and relative axial duct length.

Patrick, William P.↗

NASA NTRS1988

The effect of elastic boundary conditions on the dynamic response of rectangular plates

Natural frequencies and forced steady-state harmonic response for the vibration of uniform rectangular plates with edges elastically restrained against rotation and transverse translation are addressed. A single mode Rayleigh-Ritz solution is derived using functions that describe the normal modes of vibration of a beam whose ends are elastically restrained. The finite element solution is obtained for comparison. MACSYMA symbolic manipulation system is implemented as an aid to the mathematical rigor of the Ritz approach, and NASTRAN finite element code is used to model the mechanical system. Comparisons are made to published results and the solutions of this study are found to give lower frequencies for some values of boundary restraint. Steady-state harmonic amplitudes of displacement and acceleration are found to agree favorably for the two solutions. Low predictions of steady-state strain from NASTRAN result in some cases when compared to the Ritz values. Finally, a subjective assessment is made about the merit of using MACSYMA and NASTRAN.

Brewer, Terry K.↗

NASA NTRS1990

Rectangular subsonic jet flow field measurements

Flow field measurements of three subsonic rectangular cold air jets are presented. The three cases had aspect ratios of 1x2, 1x4 at a Mach number of 0.09 and an aspect ratio of 1x2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemometer system. The data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data are presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made.

Morrison, Gerald L.↗

NASA NTRS1990

Application of the TRANAIR rectangular grid approach to the aerodynamic analysis of complex configurations

A numerical method is described which uses a rectangular grid to solve the nonlinear full potential equation about complex configurations. The grid is locally refined to resolve high velocity gradients arising from leading edge expansions or shock waves. The grid penetrates the boundary (described by networks of quadrilateral panels) and is generated automatically. Discrete operators are constructed using the finite element method. The system of nonlinear discrete equations is solved iteratively using a Krylov subspace method preconditioned by an exterior Poisson solver and a direct sparse solver. The primary emphasis is to provide design engineers with an aerodynamic analysis tool (the TRANAIR code) which is accurate, reliable, economical, and flexible to use. Computational results for many interesting configurations are presented.

Johnson, Forrester T.↗

NASA NTRS1989

Augmented heat transfer in rectangular channels of narrow aspect ratios with rib turbulators

The effects of the rib angle-of-attack on the distributions of the local heat transfer coefficient and on the friction factors in short rectangular channels of narrow aspect ratios with a pair of opposite rib-roughened walls are determined for Reynolds numbers from 10,000 to 60,000. The channel width-to-height ratios are 2/4 and 1/4; the corresponding rib angles-of-attack are 90, 60, 45, and 30 deg, respectively. The results indicate that the narrow-aspect-ratio channels give better heat transfer performance than the wide-aspect-ratio channels for a constant pumping power. Semiempirical friction and heat transfer correlations are obtained. The results can be used in the design of turbine cooling channels of narrow aspect ratios.

Han, J. C.↗

NASA NTRS1989

Some aspects of transient cooling of a radiating rectangular medium

The emission from a gray radiating medium is analyzed for transient cooling in surroundings at a low temperature. The medium is rectangular with no variations in the direction normal to the cross section. The integral equation for the transient temperature distribution is solved numerically using a two-dimensional Gaussian integration subroutine. The emissive ability for a rectangle at uniform temperature is compared with that for transient cooling where the temperature distribution of the region has reached a fully developed shape, as shown by a separation of variables solution. The two solutions provide the upper and lower bounds for the emittance of a rectangle during transient cooling. The emittances for various aspect ratios are presented as a function of the mean length of the rectangle and are compared with results for a plane layer and a cylinder.

Siegel, Robert↗

NASA NTRS1989

On the fundamental frequency of rectangular simply-supported symmetric laminated plates

A new closed-form approximate solution for the fundamental frequency of symmetric rectangular laminates which are simply supported on all four edges is derived. The solution, obtained from eigensensitivity analysis, is expressed as a truncated Maclaurin series in the coupling stiffnesses D16 and D26. Results show that the predicted fundamental frequency is remarkably accurate. A comparison of the fundamental frequencies of four-ply symmetric angle-ply laminates calculated from the new formula with those determined from a Rayleigh-Ritz procedure yielded a maximum differential of 0.6 percent over a wide range of principal stiffness ratios, plate aspect ratios, and design angles.

Reiss, Robert↗

NASA NTRS1990

Emittance bounds for transient radiative cooling of a scattering rectangular region

Transient cooling was analyzed for a two-dimensional gray rectangular region that emits, absorbs, and isotropically scatters radiation. The region, initially at uniform temperature, is placed in surroundings at a much lower temperature. The cooling analysis yields two simultaneous equations for the transient temperature and scattering source function distributions. The region starts to cool with the medium at uniform temperature. For this condition, the local emittance around the perimeter was obtained by a numerical solution of the radiative equations, and the rate of heat loss from the entire medium was evaluated. As cooling continues, the emissive ability decreases because of the lower temperatures in the outer regions of the rectangle. Based on some previous work, a lower limit for the transient overall emittance was found by obtaining a similarity solution. For some ranges of optical thickness and scattering albedo, the lower limit is only a small amount below the initial emittance. For these conditions, the initial emittance can be used to compute the entire transient resulting in a considerable simplification.

Siegel, Robert↗

NASA NTRS1990

Vorticity, turbulence production, and turbulence induced accelerations in a rectangular jet as measured using 3-D LDA

The flow field of a rectangular jet with a 4:1 aspect ratio (50.4 x 12.7 mm) was studied at a Reynolds number of 100,000 (Mach number 0.09) using a 3-D laser Doppler anemometer system. Measurements were performed along the major and minor axis planes and at various downstream cross-sections of the jet. The mean velocity vector and entire Reynolds stress tensor were measured and presented in a previous publication. The present work presents the vorticity vector, turbulence production, and turbulence induced acceleration vector distributions which were calculated from the previously presented data.

Morrison, Gerald L.↗