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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Experimental data correlations for the effects of rotation on impingement cooling of turbine blades

The effects of rotation on impingement cooling have been experimentally studied under simulated gas turbine operating conditions. A large scale model of a blade is spun in vacuum. External heating is simulated by resistve dissipation in the thin wall of the model, which is impingement cooled. The local internal Nu is measured by an IR radiometric technique with high spatial resolution. At low rotational speeds the data agree well with published measurements taken under stationary conditions. At higher speeds, a decrease in the average Nu by up to 20-30 percent is observed. Severe gradients are generated near the hub region. Empirical correlations, which fit the data well and render it more useful for design purposes, are presented. Measurements and correlations suggest that rotational effects are very important and can cause premature blade failure.

Kreatsoulas, J. C.↗
NASA NTRS1987

Rotational effects on impingement cooling

The present consideration of rotation effects on heat transfer in a radially exhausted, impingement-cooled turbine blade model gives attention to experimental results for Reynolds and Rossby numbers and blade/coolant temperature ratio values that are representative of small gas turbine engines. On the basis of a model that encompasses the effects of Coriolis force and buoyancy on heat transfer, bouyancy is identified as the cause of an average Nusselt number that is 20-30 percent lower than expected from previous nonrotating data. A heuristic model is proposed which predicts that the impingement jets nearest the blade roots should deflect inward, due to a centripetal force generated by their tangential velocity counter to the blade motion. Potentially serious thermal stresses must be anticipated from rotation effects in the course of blade design.

Epstein, A. H.↗
NASA NTRS1988

Impingement Of Rocket Exhaust

Computer program calculates forces, heating, and contamination. Source Flow Impingement Program (SFPLIMP), a computer program that analyzes impingement of exhaust from several rocket engines on nearby surfaces in vacuum. Designed to calculate quickly undesired forces, heating, and contamination caused by firing attitude-control jets toward other surfaces of controlled spacecraft.

Drake, Bret G.↗
NASA NTRS1988

Numerical study of unsteady viscous hypersonic blunt body flows with an impinging shock

A complex two-dimensional, unsteady, viscous hypersonic shock wave interaction is numerically simulated by a high-resolution, second-order fully implicit shock-capturing scheme. The physical model consists of a nonstationary oblique shock impinging on the bow shock of a blunt body. Studies indicated that the unsteady flow patterns are slightly different from their steady counterparts. However, for the sample cases investigated the peak surface pressures for the unsteady flows seem to occur at very different impingement locations than for the steady flow cases.

Klopfer, G. H.↗
NASA NTRS1989

Numerical study of unsteady viscous hypersonic blunt body flows with an impinging shock

A complex two-dimensional, unsteady, viscous hypersonic shock wave interaction is numerically simulated by a high-resolution, second-order fully implicit shock-capturing scheme. The physical model consists of a nonstationary oblique shock impinging on the bow shock of a blunt body. Studies indicate that the unsteady flow patterns are slightly different from their steady counterparts. However, for the sample cases investigated the peak surface pressures for the unsteady flows seem to occur at very different impingement locations than for the steady flow cases.

Klopfer, G. H.↗
NASA NTRS1990

Computing Impingements Of Rocket Exhausts

SFPLIMP, Source Flow Plume Impingement Program, computes forces, moments, contamination, and heating rates caused by impingement of plumes on orbiting spacecraft from jets firing at high altitudes. User chooses among variety of configurations, data, and theories. Written in FORTRAN 77 and VAX DCL.

Cerimele, M.↗
NASA NTRS1989

Assessment of impingement effects in the isentropic core of a small satellite control thruster plume

Two computational techniques commonly employed in the calculation of rocket and thruster expansion plumes are assessed. These are the method of characteristics (MOC), which is derived from the continuum Euler equations, and the direct simulation Monte Carlo (DSMC) method, which adopts a discrete particle approach. These techniques vary both in the computational expense and in the accuracy and detail of the solutions that they provide, depending upon the regime of application. The assessment is made with reference to the plume expanding from a small monopropellant hydrazine thruster and concentrates on the isentropic core of the jet for the flow regime lying between the continuum and free molecular limits. It is found that the more numerically intensive DSMC method offers the better correspondence to the available experimental data. In addition, large differences in typical impingement effects such as drag force and heat transfer are found at the free molecular limit of the plume expansion for the two predictive techniques. It is concluded that accurate estimation of impingement potential may only be achieved through application of the discrete particle method.

Boyd, I. D.↗
NASA NTRS1990

Theoretical model of discrete tone generation by impinging jets

A new feedback mechanism is proposed for discrete tone generation by impinging jets. It is suggested that the feedback is achieved by upstream-propagating waves associated with the lowest-order intrinsic neutral wave modes of the jet flow. These wave modes have well-defined radial and azimuthal pressure and velocity distributions, which are determined by the mean flow of the jets in the case of the Kelvin-Helmholtz instability waves. The model proposed here allows the prediction of the average Strouhal number of impingement tones as a function of the jet Mach number.

Tam, Christopher K. W.↗
NASA NTRS1990

Impingement tones of large aspect ratio supersonic rectangular jets

The frequency structure of large aspect ratio jet impingement tones is analyzed. Feedback loops consisting of downstream propagating instability waves of the jet flow and upstream propagating acoustic waves from the wall to the nozzle lip produce as many as 20 or more tones when a supersonic rectangular jet of large aspect ratio is directed normal on a wall. It is seen that there are only two basic tones. The basic tone of the lower frequency is associated with a symmetric instability feedback mode of the jet, while that of the higher frequency is associated with an antisymmetric instability feedback mode. The remaining tones are combination tones of the two basic frequencies and their harmonics. It is determined that the measured basic impingement tone frequencies fall in the theoretical permissible frequency bands over a wide range of jet Mach number.

Tam, Christopher K. W.↗
NASA NTRS1991

Aerothermal study in an axial compression corner with shock impingement at Mach 6

An experimental study of an axial-compression interior-corner region with shock impingement was conducted in the NASA Langley 20-inch Mach 6 Tunnel to obtain aerodynamic heating rate distributions. The model, a generic hypersonic engine inlet, had a sharp leading edge forebody, cowl, and interchangeable struts with sharp and blunt leading edges. Experiments were conducted at free-stream unit Reynolds numbers of 1.68 x 10 to the 6th and 3.35 x 10 to the 6th per foot for the blunt and sharp-strut configurations, respectively. For the sharp-strut configuration, with and without trips, the peak heating occurred on the cowl, near the compression corner, downstream of the forebody oblique shock impingement region. The peak heating levels, for both the tripped and untripped boundary-layer flows were about 45 and 50 times the reference laminar heating levels, respectively. The peak heating for the blunt leading edge strut model, which was 30 times the reference value, occurred on the cowl, away from the corner, where the bow shock from the strut leading edge intersected the cowl surface.

Venkateswaran, S.↗
NASA NTRS1991

Effects of unsteady shock impingement on high-speed gaseous mixing

Tests are performed to determine the effects of impinging oscillating shocks of different frequencies on a 15 deg downstream angled, underexpanded, sonic helium jet injected into a supersonic airflow. Information on mixing, penetration, total pressure loss, and turbulence structure from these tests is employed to estimate mixing control achieved by adding an oscillating shock to the helium injection flow field. The principal result of this study is that impingement of an oscillating shock on a high-speed shear layer can be utilized to control the rate of mixing.

Wood, C. W.↗
NASA NTRS1993

The application of structural reliability techniques to plume impingement loading of the Space Station Freedom Photovoltaic Array

A new aerospace application of structural reliability techniques is presented, where the applied forces depend on many probabilistic variables. This application is the plume impingement loading of the Space Station Freedom Photovoltaic Arrays. When the space shuttle berths with Space Station Freedom it must brake and maneuver towards the berthing point using its primary jets. The jet exhaust, or plume, may cause high loads on the photovoltaic arrays. The many parameters governing this problem are highly uncertain and random. An approach, using techniques from structural reliability, as opposed to the accepted deterministic methods, is presented which assesses the probability of failure of the array mast due to plume impingement loading. A Monte Carlo simulation of the berthing approach is used to determine the probability distribution of the loading. A probability distribution is also determined for the strength of the array. Structural reliability techniques are then used to assess the array mast design. These techniques are found to be superior to the standard deterministic dynamic transient analysis, for this class of problem. The results show that the probability of failure of the current array mast design, during its 15 year life, is minute.

Yunis, Isam S.↗
NASA NTRS1993

Atomization characteristics of impinging liquid jets

A systematic study is presented of the atomization of impinging liquid jets investigating the effects of jet conditions (laminar versus turbulent), orifice diameter, impingement angle and jet velocity. Results are compared to current theories in terms of sheet breakup length, sheet shape and drop size. Experiments contrasting laminar and turbulent jet conditions clearly show that the jet conditions have a dramatic effect on the atomization process.

Ryan, H. M.↗
NASA NTRS1993

The Application of Structural Reliability Techniques to Plume Impingement Loading of the Space Station Freedom Photovoltaic Array

A new aerospace application of structural reliability techniques is presented, where the applied forces depend on many probabilistic variables. This application is the plume impingement loading of the Space Station Freedom Photovoltaic Arrays. When the space shuttle berths with Space Station Freedom it must brake and maneuver towards the berthing point using its primary jets. The jet exhaust, or plume, may cause high loads on the photovoltaic arrays. The many parameters governing this problem are highly uncertain and random. An approach, using techniques from structural reliability, as opposed to the accepted deterministic methods, is presented which assesses the probability of failure of the array mast due to plume impingement loading. A Monte Carlo simulation of the berthing approach is used to determine the probability distribution of the loading. A probability distribution is also determined for the strength of the array. Structural reliability techniques are then used to assess the array mast design. These techniques are found to be superior to the standard deterministic dynamic transient analysis, for this class of problem. The results show that the probability of failure of the current array mast design, during its 15 year life, is minute.

Yunis, Isam S.↗
NASA NTRS1931

Development of an Impinging-jet Fuel-injection Valve Nozzle

During an investigation to determine the possibilities and limitations of a two-stroke-cycle engine and ignition, it was necessary to develop a fuel injection valve nozzle to produce a disk-shaped, well dispersed spray. Preliminary tests showed that two smooth jets impinging upon each other at an angle of 74 degrees gave a spray with the desired characteristics. Nozzles were built on this basis and, when used in fuel-injection valves, produced a spray that fulfilled the original requirements. The spray is so well dispersed that it can be carried along with an air stream of comparatively low velocity or entrained with the fuel jet from a round-hole orifice. The characteristics of the spray from an impinging-jet nozzle limits its application to situations where wide dispersion is required by the conditions in the engine cylinder and the combustion chamber.

Spanogle, J A↗
NASA NTRS1991

The 1991 version of the plume impingement computer program. Volume 2: User's input guide

The Plume Impingement Program (PLIMP) is a computer code used to predict impact pressures, forces, moments, heating rates, and contamination on surfaces due to direct impingement flowfields. Typically, it has been used to analyze the effects of rocket exhaust plumes on nearby structures from ground level to the vacuum of space. The program normally uses flowfields generated by the MOC, RAMP2, SPF/2, or SFPGEN computer programs. It is capable of analyzing gaseous and gas/particle flows. A number of simple subshapes are available to model the surfaces of any structure. The original PLIMP program has been modified many times of the last 20 years. The theoretical bases for the referenced major changes, and additional undocumented changes and enhancements since 1988 are summarized in volume 1 of this report. This volume is the User's Input Guide and should be substituted for all previous guides when running the latest version of the program. This version can operate on VAX and UNIX machines with NCAR graphics ability.

Bender, Robert L.↗
NASA NTRS1993

Experiments on the ground vortex formed by an impinging jet in cross flow

An inclined jet impinging on the ground creates a wall flow that spreads radially from the point of impingement. If a cross-flow is introduced, the upstream component of the wall flow will separate from the ground and create what has been termed the 'ground vortex.' The ground vortex has been shown to have a significant impact on aircraft aerodynamics and is one of the major contributors to hot gas ingestion. The paper discusses a recent study which included a generic wing-body configuration for assessing the impact of the ground vortex on configuration aerodynamics. Wind tunnel tests using fixed ground boards, moving ground belts, and moving model tests are discussed. The emphasis of the data is macroscopic, i.e. forward location of the vortex, effects of ground height, etc.

Blake, William B.↗
NASA NTRS1995

Cleaning verification by air/water impingement

This paper will discuss how the Kennedy Space Center intends to perform precision cleaning verification by Air/Water Impingement in lieu of chlorofluorocarbon-113 gravimetric nonvolatile residue analysis (NVR). Test results will be given that demonstrate the effectiveness of the Air/Water system. A brief discussion of the Total Carbon method via the use of a high temperature combustion analyzer will also be given. The necessary equipment for impingement will be shown along with other possible applications of this technology.

Jones, Lisa L.↗