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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,207 records · Page 67
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NASA NTRS1984

SSME thrust chamber simulation using Navier-Stokes equations

The capability of the PHOENICS fluid dynamics code in predicting two-dimensional, compressible, and reacting flow in the combustion chamber and nozzle of the space shuttle main engine (SSME) was evaluated. A non-orthogonal body fitted coordinate system was used to represent the nozzle geometry. The Navier-Stokes equations were solved for the entire nozzle with a turbulence model. The wall boundary conditions were calculated based on the wall functions which account for pressure gradients. Results of the demonstration test case reveal all expected features of the transonic nozzle flows. Of particular interest are the locations of normal and barrel shocks, and regions of highest temperature gradients. Calculated performance (global) parameters such as thrust chamber flow rate, thrust, and specific impulse are also in good agreement with available data.

Przekwas, A. J.↗
NASA NTRS1985

Generation of capillary instabilities by external disturbances in a liquid jet

The receptivity problem in a circular liquid jet is considered. A time harmonic axial pressure gradient is imposed on the steady, parallel flow of a jet of liquid emerging from a circular duct. Using a technique developed in plasma physics a casual solution to the forced problem is obtained over certain ranges of Weber number for a number of mean velocity profiles. This solution contains a term which grows exponentially in the downstream direction and can be identified with a capillary instability wave. Hence, it is found that the externally imposed disturbances can indeed trigger instability waves in a liquid jet. The amplitude of the instability wave generated relative to the amplitude of the forcing is computed numerically for a number of cases.

Leib, S. J.↗
NASA NTRS1985

Flat-plate transition

A new research effort was undertaken to build a boundary-layer transition tunnel. This facility only recently became operational. The data obtained so far are merely qualitative. The main goal is to predict heat transfer given any combination of factors such as pressure gradient, turbulence level, Reynolds number, or intermittency factor. The boundary-layer transition tunnel is a closed-loop tunnel that controls the turbulence level, velocity and temperature of the air within it. Problems associated with the operation of this tunnel are examined.

Ercegovic, B. A.↗
NASA NTRS1985

A review and analysis of boundary layer transition data for turbine application

A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information. The data were analyzed by using a version of the STAN5 two-dimensional boundary layer code. The transition starting and ending points were determined by adjusting parameters in STAN5 until the calculations matched the data. The results are presented as a table of the deduced transition location and length as functions of the test parameters. The data sets reviewed cover a wide range of flow conditions, from low-speed, flat-plate tests to full-scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free-stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Gaugler, R. E.↗
NASA NTRS1985

Experimental investigations on airfoils with different geometries in the domain of high angles of attack-flow separation

Wind tunnel tests were conducted on airfoil models in order to study the flow separation phenomena occurring for high angles of attack. Pressure distribution on wings of different geometries were measured. Results show that for three-dimensional airfoils layout and span lift play a role. Separation effects on airfoils with moderate extension are three-dimensional. The flow domains separated from the air foil must be treated three-dimensionally. The rolling-up of separated vortex layers increases with angle in intensity and induction effect and shows strong nonlinearities. Boundary layer material moves perpendicularly to the flow direction due to the pressure gradients at the airfoil; this has a stabilizing effect. The separation starts earlier with increasing pointed profiles.

Keil, J.↗
NASA NTRS1985

A cosmic ray driven instability

The interaction between energetic charged particles and thermal plasma which forms the basis of diffusive shock acceleration leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homogeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves.

Dorfi, E. A.↗
NASA NTRS1985

A space-marching method for incompressible Navier-Stokes equations

This paper deals with the development of a space-marching method for incompressible flows. The method solves the continuity and momentum equations as a coupled system at each streamwise station. The character of the system of equations has been changed from elliptic to hyperbolic/parabolic in order to enable the equations to be marched in space. The present method has many advantages compared to the existing parabolic or space-marching methods for incompressible flow: (1) it avoids the solution of Poisson equations, (2) it conserves the mass flow with no additional computation, (3) it does not require the specification of an assumed pressure field when used in the prediction of duct flows. The present method can capture strong secondary velocities and strong transverse pressure gradients. Predictions of the flow through straight and curved ducts are in good agreement with analytical and experimental results.

Pouagare, M.↗
NASA NTRS1985

Potential flow calculations and preliminary wing design in support of an NLF variable sweep transition flight experiment

NASA Langley and NASA Ames-Dryden have defined a variable-sweep transition-flight experiment utilizing the F-14 aircraft to enhance understanding of the interaction of crossflow and Tollmien-Schlichting instabilities on a laminar-boundary-layer transition. The F-14 wing outer panel will be modified to generate favorable pressure gradients on the upper wing surface over a wide range of flight conditions. Extensive computations have been performed using two-dimensional and three-dimensional transonic analysis codes. Flight-test and computational data are compared and shown to validate the applicability of the three-dimensional codes (WBPPW and TAWFIVE). In addition, results from two preliminary glove designs derived from two different approaches to the design problem are presented. Advantages and disadvantages of each approach are identified, and it is concluded that coupling an analysis code with an automated design procedure yields a powerful code with distinct advantages over a 'cut-and-dry' approach.

Waggoner, E. G.↗
NASA NTRS1985

Experiments on the stability of crossflow vortices in swept-wing flows

Experiments are conducted which demonstrate the feasibility of creating crossflow vortices in a flat-plate flow. A swept leading edge and contoured wind-tunnel walls produce a strong pressure gradient and a typical swept-wing flow on the plate. Detailed three-dimensional measurements, made within the boundary layer using hot-wire anemometry, are supplemented with different flow-visualization techniques. Data are presented on the mean flow characteristics as well as on the behavior of the crossflow vortices. Comparisons are made with theoretical flow-field and stability calculations.

Saric, W. S.↗
NASA NTRS1984

Convergent-tapered annular seals - Analysis and testing for rotordynamic coefficients

A combined analytical-computational method has been developed to calculate the pressure field and dynamic coefficients for tapered high-pressure annular seals. Completely developed turbulent flow is assumed in both the circumferential and axial directions, according to Hirs' (1973) bulk-flow turbulent-lubrication equations. In a numerical experiment with the method, a short bearing approximation is used to derive an analytical expression for the first-order (dynamic) pressure gradient. This expression is integrated numerically to define dynamic coefficients of the seal. Numerical results of the integration are compared with previous results for straight and tapered seals. It is found that direct stiffness and leakage coefficients increase in the present seal, while the remaining coefficients decrease. An optimal taper angle is shown to exist with respect to: (1) the direct stiffness and (2) the ratio of direct stiffness to leakage. On the basis of the optimal taper angle calculations, stiffness increases on the order of 40 to 50 percent are predicted. Experimental results for three taper angles are presented, and are found to be in good agreement with the theoretical predictions.

Childs, D. W.↗
NASA NTRS1985

Chemistry in dynamically evolving clouds

A unified model of chemical and dynamical evolution of isolated, initially diffuse and quiescent interstellar clouds is presented. The model uses a semiempirically derived dependence of the observed cloud temperatures on the visual extinction and density. Even low-mass, low-density, diffuse clouds can collapse in this model, because the inward pressure gradient force assists gravitational contraction. In contrast, previous isothermal collapse models required the low-mass diffuse clouds to be unrealistically cold before gravitational contraction could start. Theoretically predicted dependences of the column densities of various atoms and molecules, such as C and CO, on visual extinction in diffuse clouds are in accord with observations. Similarly, the predicted dependences of the fractional abundances of various chemical species (e.g., CO, H2CO, HCN, HCO(+)) on the total hydrogen density in the core of the dense clouds also agree with observations reported to date in the literature. Compared with previous models of interstellar chemistry, the present model has the potential to explain the wide spectrum of chemical and physical properties of both diffuse and dense clouds with a common formalism employing only a few simple initial conditions.

Tarafdar, S. P.↗
NASA NTRS1984

Sintered plug flow modulation of a vapor-liquid phase separator for a helium II vessel

Presented is a system for modulation of a superfluid (helium II) flow in a vapor-liquid phase separator, for use in cryogenic storage tanks in future space missions. The system consists of a semicircular mechanically operated shutter, downstream of the separator plug, rotated at 0.1 rpm to control the operational surface area of the separator. The mass flow rate was varied from 10 to 22 mg/s. Pressure gradients across the plug are also discussed.

Frederking, T. H. K.↗
NASA NTRS1985

Hybrid approach to steady transonic normal shock-compressible laminar boundary layer interactions over airfoils with suction

Transonic airfoil flow is to a large degree affected by viscous-inviscid interactions. Among them a key role is played by the boundary layer interaction with the shock wave embedded in the flow field and the interaction of the boundary layer with the sustained adverse pressure gradients. The effects of these interactions can be controlled or suppressed by introducing surface mass transfer such as suction. This investigation deals strictly with the study of shock-laminar boundary layer interactions including distributed mass transfer. The present calculations agree with experiments on a swept LFC wing at low speeds which indicates that with a suitable choice of the extent of the airfoil surface over which suction is applied and adjustment of the suction velocity, full-chord laminar flow can be maintained and separation can be prevented completely.

Ram, R. B.↗
NASA NTRS1985

Control plate for shock-boundary layer interaction

Paper describes tests and computations for a relatively unique technique to greatly reduce/eliminate the separation region for shock-boundary layer interactions. A number of studies have shown that the usual effects of such interactions include increased local heating and wall pressures, thickening of the boundary layer and a decrease in the momentum of the flow and, for stronger waves, flow separation. This flow situation is particularly prevalent in supersonic and hypersonic inlets where severe performance degradation can occur due to flow separation. High performance engine design generally requires a uniform entering flow field with little stagnation pressure loss. Previous approaches to the problem involved primarily active devices (e.g., suction or blowing); the present paper considers a passive device. The boundary layer separation control technique considered herein involves the placement of an embedded plate in the outer portion of the boundary layer and parallel to the wall. This control plate is situated such that the incident shock impinges upon and reflects from its surface, thus greatly lessening the pressure gradient in the low momentum near wall region.

Goodman, W. L.↗
NASA NTRS1985

Vortex induced lift on a flat plate with a curved forward-facing flap

Free streamline solutions are obtained for two-dimensional inviscid incompressible flow past a flat plate with a forward-facing curved flap. It is shown that it is possible to shape the curved flap to make the adverse pressure gradient on top of the flap less severe than for a straight flap and thus increase the prospects of making the flow experimentally realizable.

Tanveer, S.↗
NASA NTRS1985

AMPTE/CCE energetic particle composition measurements during the September 4, 1984 magnetic storm

The results of measurements for the magnetic-storm period of September 4-7, 1984 from the medium-energy particle analyzer (MEPA) on the CCE spacecraft are presented. It is shown that within L-shells of about 2.5 to 5 in the dusk sector near the equatorial plane, the enhancement factor in the fluxes for the CNO group is greater than that of helium, which is greater than that of protons. The flux ratios of helium and CNO over all ions at the same total energy show considerable increases in the same L-shell ranges. For the particle population measured by MEPA, a local current-density enhancement of about 0.5 nA/sq m is found over the L range of 3.5 to 6 during the magnetic storm. It is found that the total current density is dominated by the pressure-gradient current of the protons.

Mcentire, R. W.↗
NASA NTRS1985

The Goertler vortex instability mechanism in three-dimensional boundary layers

The two-dimensional boundary layer on a concave wall is centrifugally unstable with respect to vortices aligned with the basic flow for sufficiently high values of the Goertler number. However, in most situations of practical interest the basic flow is three-dimensional and previous theoretical investigations do not apply. The linear stability of the flow over an infinitely long swept wall of variable curvature is considered. If there is no pressure gradient in the boundary layer the instability problem can always be related to an equivalent two-dimensional calculation. However, in general, this is not the case and even for small values of the crossflow velocity field dramatic differences between the two and three-dimensional problems emerge. When the size of the crossflow is further increased, the vortices in the neutral location have their axes locally perpendicular to the vortex lines of the basic flow.

Hall, P.↗
NASA NTRS1985

Structure of ducted particle-laden turbulent jets

New and existing measurements have been used to develop and evaluate models of particle-laden jets and sprays, yielding encouraging results for a stochastic separated flow (SSF) model which treats effects of interphase slip and turbulence on the basis of random walk computations of particle or drop motion. An evaluation of the SSF model using the measurements of Modarress et al. (1982, 1983) yielded results comparable to earlier work, suggesting that data from coflowing jets in ducts should be accompanied by static pressure measurements, since even small pressure gradients appreciably influence jet properties.

Zhang, Q.-F.↗