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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Analysis of flight effects on noise radiation from dual-flow coaxial jets

A theoretical study has been made of the effects of flight on noise from dual-flow coaxial jets. The theory is based on an instability free, vortex sheet flow model. It is shown that the flight effects are more favorable (and hence produce less forward-arc amplification) for coaxial jets than for single-stream jets. Further, the theory predicts that, like the single-stream jet case, flight effects induce noise amplification in the forward quadrant and attenuation in the aft quadrant and have virtually no effect at theta = 90 deg to the jet axis, where theta is the angle between the directions of convection and emission at the retarded time. Amplification in the forward quadrant diminishes as the inner flow velocity increases and becomes optimum when the outer-to-inner velocity ratio is about 0.5. The theory also shows that the higher the outer-to-inner area ratio, the lower the forward-arc amplification due to flight.

Dash, R.↗
NASA NTRS1976

Review of coaxial flow gas core nuclear rocket fluid mechanics

Almost all of the fluid mechanics research associated with the coaxial flow gas core reactor ended abruptly with the interruption of NASA's space nuclear program because of policy and budgetary considerations in 1973. An overview of program accomplishments is presented through a review of the experiments conducted and the analyses performed. Areas are indicated where additional research is required for a fuller understanding of cavity flow and of the factors which influence cold and hot flow containment. A bibliography is included with graphic material.

Weinstein, H.↗
NASA NTRS1971

Supersonic jet noise suppression using coaxial flow interaction.

The scope of investigations conducted with coaxial interacting supersonic jet flows covers (1) acoustic measurements in both the far noise field and near noise field, (2) surveys of mean flow properties and fluctuating pressures, optical visualization of interacting jet flows, the associated flow and shock structure changes and the noise field, (3) the effects of different geometrical parameters of the coaxial nozzles, and (4) thrust measurements. It is shown that the flow interaction between two suitable controlled interacting coaxial supersonic axisymmetric jet flows results in substantial noise reduction based on equivalent thrust considerations. This flow interaction technique appears to be potentially an attractive approach for suppression of noise from supersonic jet exhausts.

Dosanjh, D. S.↗
NASA NTRS1981

Numerical analysis of turbulent coaxial flow with internal heat generation

A computational method with which to obtain a physical understanding of the turbulent field of two coaxial jets entering an axisymmetric chamber is developed. Even the laminar field of this flow is quite complicated. This is due to the many different domains which exist in the field especially in the entrance region. Physically, three regions may be identified: the wall region, the initial region near the axis of symmetry and the mixing region. Advancing downstream, these regions change relative size with the ratio of the two jets' mass fluxes as the main parameter. The turbulent field of these flows is much more complicated due to the difference in the effective transport coefficients and turbulence level from region to region. However, being aware beforehand of the complications and the different regions of this field, the appropriate turbulence model and numerical scheme can be adjusted to treat the problem.

Lin, A.↗
NASA NTRS1960

A Coaxial Flow Reactor - A Gaseous Nuclear-Rocket Concept

Aspects of a new gaseous nuclear-rocket concept are considered. The principle of this type of cavity reactor is one of maintaining the separation of two coaxial streams - fuel within propellant - rather than attaining the separation of fuel propellant gases within the cavity. An acceptably low uranium consumption rate is possible if the fuel stream can be maintained at an axial velocity which is 1/100 to 1/1000 of the propellant velocity. An elementary hydrodynamic analysis for laminar incompressible flow indicates that the average uranium core velocity may only reach 2 to 11 times the initial core velocity for a typical reactor. The results of a 1-D criticality analysis for a D2O/(235)U system show that the effect of shrinking the fuel region within the reactor cavity is not serious; the effects of moderator heating and structural materials on critical mass are also shown. Overall rocket performance calculations are made for reasonable operating conditions; these results indicate that thrusts from 25,000 to 50,000 pounds and accelerations from 10(exp -1) to 3 g are possible.

Robert G Ragsdale↗
NASA NTRS1976

Review of coaxial flow gas core nuclear rocket fluid mechanics

The two areas where discussion and comparison of work is most useful are in (1) the factors which influence containment in cold flow studies; and (2) the effects of heat generation on containment. The work in these areas have not received any critical review in the past. The review is structured in such a way as to compare and contrast the related work of the program, rather than to preserve the chronological order of the work.

Weinstein, H.↗
NASA NTRS2016

Coaxial Rotor Flow Phenomena in Forward Flight

Coaxial rotors are nding use in advanced rotorcraft concepts. Combined with lift offset rotor technology, they offer a solution to the problems of dynamic stall and re-verse ow that often limit single rotor edgewise forward ight speeds. Lower tip speed means reduced high-speed impulsive noise. The need for an anti-torque tail rotor is eliminated, a major boon during operation in conned areas. However, the operation of two counter-rotating ro-tors in close proximity generates many possibilities for aerodynamic interactions between rotor blades, blades and vortices, and between vortices. The parameter de-sign space is very large, and requires efcient computations as well as basic experiments to explore important physics to determine performance, loads, and acoustics. Computations are done on the classic HarringtonDingeldein rotor test case from the 1950s using the ROTUNS Navier Stokes code. Two regimes are explored: very low advance ratio as a perturbation from hover, and high advance ratio. Flow eld properties from RotUNS are used with 2-D OVERFLOW computations to capture blade crossing effects including those of higher subsonic Mach numbers. Bladeblade and bladevortex intersection events are captured using a MatLab-based predictor.

Flow Phenomena↗
NASA NTRS1975

Investigation B: Laminar confined coaxial entrance flow with heat generation

The results of a parametric study on the entrance flow region in a gas core nuclear reactor are presented. The physical system is modeled as laminar confined, coaxial flow with heat generation in the inner fluid. The governing equations include the boundary layer approximations and the assumptions of only radial radiative transport of energy represented as an energy diffusion term. The Von Mises transformation and a zeta transformation are used to transform the equations into nonlinear nonhomogeneous convective-diffusion equations. A unique combination of forward and backward difference equations which yields accurate results at moderate computational times, is used in the numerical method. Results show that the rapidly accelerating, heat generating inner stream actually shrinks in radius as it expands axially.

Bobba, G. K. M.↗
NASA NTRS1982

Effects of flight on noise radiated from convected ring sources in coaxial dual flow. Part 2: The noise from heated jets

The effects of flight on noise from heated jets are discussed. The effects of the additionally, extraneously-generated dipole and simple source terms which arise as a result of the density gradients across the fluid interfaces were incorporated. The coaxial flows with inverted profiles are shown to be quieter than the conventional profiles; however, the benefit of noise reduction at higher outer-to-inner area ratios is totally offset as the inverted profile incurs a significant massloss and thrust-loss. Amongst all the possible coaxial configurations when on of the coaxial streams is heated-conventional profile (CP), inverted profile (IP) and the variable stream control engine (VSCE) cycle-and at constant massflow and thrust, a VSCE-cycle is the most desirable and the best possible engine cycle inasmuch as it provides over more than 18.0 dB reduction in SPL (as compared against noise from a CP-cycle) at all angles, both statically and in flight, for area ratios Sigma 0.25.

Dash, R.↗