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At least 73 records · Page 4

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Effects of rotation on impingement cooling of turbine blades

The effects of rotation on impingement cooling of turbine blades were studied experimentally as a specialized facility at M.I.T. A foil heated resistively was cooled by a jet flow on one side and temperature monitored on the other. Rotating the blade limits the heat transfer path to conduction through the support structure and radiation. IR radiometry furnishes the temperature distributions on the chamber wall, permitting the internal heat transfer coefficient to be measured. The heat transfer efficiency has been found to fall as much as 30 percent as rotational speed increases. The conditions observed confirm the significance of rotational effects, particularly with regard to potential early blade failure.

Kreatsoulas, J. C.↗

NASA NTRS1982

Experimental and analytical determination of gear tooth temperatures with oil jet lubrication

Gear tooth average and instantaneous surface temperatures were measured with a fast response infrared radiometric microscope, while operating at arious speeds, loads and oil jet pressures. Increased oil jet pressure had a significant effect on both average and peak surface temperatures at all test conditions, increasing the speed at constant load and increasing the load at constant speed causes a significant rise in average and peak surface temperatures of gear teeth. A gear tooth temperature analysis was conducted by a finite element method combined with a calculated heat input and oil jet impingment depth with estimated heat transfer coefficients based on the experimental data. It is concluded that oil jet pressures required for adequate cooling at high load and speed conditions must be high enough to get full penetration depth of the teeth.

Townsend, D. P.↗

DOE OSTI2023

Numerical Simulations of High Prandtl Number Liquid Jets Impinging on a Flat Plate

In this work, 3D simulations of oil jets impinging on a flat, heated wall are presented. The numerical setup uses the Volume of Fluid (VoF) method to model the two-phase flow. A careful grid definition across the liquid film, along with the use of the Conjugate Heat Transfer (CHT) approach allowed local heat transfer to be solved with fine resolution at the wall. Variations of liquid flow rate, liquid temperature and surface temperature allow to cover a wide range of local Reynolds and Prandtl numbers (226 < Re < 2850, 77 < Pr < 161). Resulting surface-averaged heat transfer compares very well with experimental measurements conducted in a previous study. In-depth analysis of the flow has identified expected features from the literature. In particular, the impact of jet axial velocity profiles on the heat transfer distribution in the stagnation zone was clearly stated. The increase in heat transfer when warming the liquid film was also reproduced and explained by a decrease in oil viscosity and an increase in film velocity. All those effects were taken into account in correlations for stagnation and local values of Nusselt number. A grid sensitivity study was also conducted, showing that if the grid solving the thermal boundary layer in the stagnation zone can be coarsened without impacting local and surface-averaged predictions of heat transfer, a minimum resolution (2 to 3 cells) within the thermal boundary layer is however required for an accurate prediction of heat transfer.

conjugate heat transfer↗

NASA NTRS1973

Impingement heat transfer from turbulent air jets to flat plates: A literature survey

Heat transfer characteristics of single and multiple turbulent air jets impinging on flat surfaces have been studied by many investigators. Results of many of these studies are summarized. Suggested correlations for use in the design of cooled turbine blades are noted, and areas where further research would be advisable are identified.

Livingood, J. N. B.↗

DOE OSTI2022

Impingement panel for a turbomachine

An integrated combustor nozzle includes a combustion liner that extends radially between an inner liner segment and an outer liner segment. The combustion liner includes a forward end portion, an aft end portion, a first side wall, and a second side wall. The aft end portion of the combustion liner defines a turbine nozzle. The integrated combustor nozzle further includes an impingement panel having an impingement plate disposed along an exterior surface of one of the inner liner segment or the outer liner segment. The impingement plate defines a plurality of impingement holes that direct coolant in discrete jets towards the exterior surface of the inner liner segment or the outer liner segment. The impingement panel is radially spaced from the exterior surface to form a cooling flow gap therebetween. The impingement panel includes a collection duct that extends from the impingement panel and defines a collection passage.

Berry, Jonathan Dwight↗

NASA NTRS1993

Computational analysis of hypersonic shock wave/wall jet interaction

The purpose of this study is to investigate the CFD code General Aerodynamic Simulation Program (GASP) for application to a specific scramjet combustor phenomenon, that of an adverse pressure gradient caused by an oblique shock wave impinging upon a wall cooling film. The basis of this investigation is data available from an existing experimental study, which includes wall pressure, wall heat transfer, and schlieren photographs. This experimental study was conducted at a nominal Mach number of 6.0 in the Calspan 48-inch shock tunnel. The particular case of interest generates flow separation at the shock impingement point. Two algebraic turbulence models, the Baldwin-Lomax model and the Goldberg model, are considered for this computational study. Resultant computational wall pressure and heat transfer for both turbulence models are compared with experimental data. The Goldberg turbulence model provides a more accurate prediction of the recirculation region, and as a result, a better comparison with the experimental data.

Mekkes, Gregory L.↗

NASA NTRS1982

Jet array impingement flow distributions and heat transfer characteristics. Effects of initial crossflow and nonuniform array geometry

Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. The configurations considered are intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The effects of an initial crossflow which approaches the array through an upstream extension of the channel are considered. Flow distributions as well as heat transfer coefficients and adiabatic wall temperatures resolved to one streamwise hole spacing were measured as a function of the initial crossflow rate and temperature relative to the jet flow rate and temperature. Both Nusselt number profiles and dimensionless adiabatic wall temperature (effectiveness) profiles are presented and discussed. Special test results which show a significant reduction of jet orifice discharge coefficients owing to the effect of a confined crossflow are also presented, along with a flow distribution model which incorporates those effects. A nonuniform array flow distribution model is developed and validated.

Florschuetz, L. W.↗

NASA NTRS1990

Shock interference heating in scramjet engines

Experimental and analytical research sponsored by the NASA Langley Research center and the NASP Structures Technology Maturation Program to define critical aerothermal loads for the NASP engine is summarized. Presented is a review of (1) shock-shock interaction on the engine cowl leading edge that results in a supersonic jet impinging on the leading edge surface and causes the heat transfer rate to be amplified by a factor of 30 or more over the undisturbed (no shock interaction) flow stagnation point heat transfer rate, (2) the effectiveness of supersonic film cooling with and without the effects of an impinging oblique shock wave, and (3) oblique shock impingement in an axial compression corner.

Wieting, Allan R.↗

NASA NTRS1982

The CF6 Jet Engine Performance Improvement - Low Pressure Turbine Active Clearance Control

A low pressure turbine (LPT) active clearance control (ACC) cooling system was developed to reduce the fuel consumption of current CF6-50 turbofan engines for wide bodied commercial aircraft. The program performance improvement goal of 0.3% delta sfc was determined to be achievable with an improved impingement cooling system. The technology enables the design of an optimized manifold and piping system which is capable of a performance gain of 0.45% delta sfc.

Beck, B. D.↗

NASA NTRS1989

Lubricant Jet Flow Phenomena in Spur and Helical Gears with Modified Addendums; for Radially Directed Individual Jets

This paper develops the mathematical relations for the Virtual Kinetic Model as an improvement over the vectorial model developed earlier. The model solution described provides the most energy efficient means of cooling gears, i.e., it requires the least pressure or pumping power to distribute the coolant onto the tooth surface. Further, this nozzle orientation allows impingement to the root of the tooth if needed and provides the most cooling control when compared to into-mesh and out-of-mesh cooling.

Akin, Lee S.↗

NASA NTRS1989

Lubricant jet flow phenomena in spur and helical gears with modified addendums - For radially directed individual jets

Akin, L. S.↗

NASA NTRS2003

Evaluation of Impinging Stream Vortex Chamber Concepts for Liquid Rocket Engine Applications

NASA Marshall Space Flight Center (MSFC) and the U. S. Army are jointly investigating vortex chamber concepts for cryogenic oxygen/hydrocarbon fuel rocket engine applications. One concept, the Impinging Stream Vortex Chamber Concept (ISVC), has been tested with gel propellants at AMCOM at Redstone Arsenal, Alabama. A version of this concept for the liquid oxygen (LOX)/hydrocarbon fuel (RP-1) propellant system is derived from the one for the gel propellant. An unlike impinging injector is employed to deliver the propellants to the chamber. MSFC has also designed two alternative injection schemes, called the chasing injectors, associated with this vortex chamber concept. In these injection techniques, both propellant jets and their impingement point are in the same chamber cross-sectional plane. One injector has a similar orifice size with the original unlike impinging injector. The second chasing injector has small injection orifices. The team has achieved their objectives of demonstrating the self-cooled chamber wall benefits of ISVC and of providing the test data for validating computational fluids dynamics (CFD) models. These models, in turn, will be used to design the optimum vortex chambers in the future.

Trinh, Huu↗

NASA NTRS1972

Average heat-transfer characteristics of a row of circular air jets impinging on a concave surface

A study of the average heat-transfer characteristics of air jets impinging on the concave side of a right-circular semicylinder is reported. Results from existing correlating are compared with each other and with experimental heat-transfer data for a row of circular jets. Two correlations available in the literature are recommended for use in designing cooled turbine vanes and blades.

Livingood, J. N. B.↗

NASA NTRS1999

Optical Imaging of Flow Pattern and Phantom

Time-resolved optical imaging technique has been used to image the spatial distribution of small droplets and jet sprays in a highly scattering environment. The snake and ballistic components of the transmitted pulse are less scattered, and contain direct information about the sample to facilitate image formation as opposed to the diffusive components which are due to multiple collisions as a light pulse propagates through a scattering medium. In a time-gated imaging scheme, these early-arriving, image-bearing components of the incident pulse are selected by opening a gate for an ultrashort period of time and a shadowgram image is detected. Using a single shot cooled CCD camera system, the formation of water droplets is monitored as a function of time. Picosecond time-gated image of drop in scattering cells, spray droplets as a function of let speed and gas pressure, and model calcification samples consisted of calcium carbonate particles of irregular shapes ranging in size from 0. 1 to 1.5 mm affixed to a microscope slide have been measured. Formation produced by an impinging jet will be further monitored using a CCD with 1 kHz framing illuminated with pulsed light. The desired image resolution of the fuel droplets is on the 20 pm scale using early light through a highly scattering medium. A 10(exp -6)m displacement from a jet spray with a flow speed of 100 m/sec introduced by the ns grating pulse used in the imaging is negligible. Early ballistic/snake light imaging offers nondestructive and noninvasive method to observe the spatial distribution of hidden objects inside a highly scattering environment for space, biomedical, and materials applications. In this paper, the techniques we will present are time-resolved K-F transillumination imaging and time-gated scattered light imaging. With a large dynamic range and high resolution, time-gated early light imaging has the potential for improving rocket/aircraft design by determining jets shape and particle sizes. Refinements to these techniques may enable drop size measurements in the highly scattering, optically dense region of multi-element rocket injectors. These types of measurements should greatly enhance the design of stable, and higher performing rocket engines.

Galland, Pierre A.↗

NASA NTRS1983

Study of lubricant jet flow phenomena in spur gears: Out of mesh condition

The penetration depth onto the tooth flank of a jet of oil at different velocities pointed at the pitch line on the outgoing side of mesh was determined. The analysis determines the impingement depth for both the gear and the pinion. It includes the cases for speed increasers and decreasers as well as for one to one gear ratio. In some cases the jet will strike the loaded side of the teeth, and in others it will strike the unloaded side of the teeth. In nearly all cases the top land will be cooled regardless of the penetration depth, and postimpingement oil spray will usually provide adequate amounts of oil for lubrication but is marginal or inadequate for cooling.

Townsend, D. P.↗

NASA NTRS1994

Experimental studies of shock-wave/wall-jet interaction in hypersonic flow

Experimental studies have been conducted to examine slot film cooling effectiveness and the interaction between the cooling film and an incident planar shock wave in turbulent hypersonic flow. The experimental studies were conducted in the 48-inch shock tunnel at Calspan at a freestream Mach number of close to 6.4 and at a Reynolds number of 35 x 10(exp 6) based on the length of the model at the injection point. The Mach 2.3 planar wall jet was generated from 40 transverse nozzles (with heights of both 0.080 inch and 0.120 inch), producing a film that extended the full width of the model. The nozzles were operated at pressures and velocities close to matching the freestream, as well as at conditions where the nozzle flows were over- and under-expanded. A two-dimensional shock generator was used to generate oblique shocks that deflected the flow through total turnings of 11, 16, and 21 degrees; the flows impinged downstream of the nozzle exits. Detailed measurements of heat transfer and pressure were made both ahead and downstream of the injection station, with the greatest concentration of measurements in the regions of shock-wave/boundary layer interaction. The major objectives of these experimental studies were to explore the effectiveness of film cooling in the presence of regions of shock-wave/boundary layer interaction and, more specifically, to determine how boundary layer separation and the large recompression heating rates were modified by film cooling. Detailed distributions of heat transfer and pressure were obtained in the incident shock/wall-jet interaction region for a series of shock strengths and impingement positions for each of the two nozzle heights. Measurements were also made to examine the effects of nozzle lip thickness on cooling effectiveness. The major conclusion from these studies was that the effect of the cooling film could be readily dispersed by relatively weak incident shocks, so the peak heating in the recompression region was not significantly reduced by even the largest levels of film cooling. For the case studies in the absence of film cooling, the interaction regions were unseparated. However, adding film cooling resulted in regions of boundary layer separation induced in the film cooling layer -- the size of which regions first increased and then decreased with increased film cooling. Surprisingly, the size of the separated regions and the magnitude of the recompression heating were not strongly influenced by the thickness of the cooling film, nor by the point of shock impingement relative to the exit plane of the nozzles. The lip thickness was found to have little effect on cooling effectiveness. Measurements with and in the absence of shock interaction were compared with the results of earlier experimental studies and correlated in terms of the major parameters controlling these flows.

Holden, Michael S.↗

NASA NTRS1994

Experimental studies of shock-wave/wall-jet interaction in hypersonic flow, part A

Experimental studies have been conducted to examine slot film cooling effectiveness and the interaction between the cooling film and an incident planar shock wave in turbulent hypersonic flow. The experimental studies were conducted in the 48-inch shock tunnel at Calspan at a freestream Mach number of close to 6.4 and at a Reynolds number of 35 x 10(exp 6) based on the length of the model at the injection point. The Mach 2.3 planar wall jet was generated from 40 transverse nozzles (with heights of both 0.080 inch and 0.120 inch), producing a film that extended the full width of the model. The nozzles were operated at pressures and velocities close to matching the freestream, as well as at conditions where the nozzle flows were over- and under-expanded. A two-dimensional shock generator was used to generate oblique shocks that deflected the flow through total turnings of 11, 16, and 21 degrees; the flows impinged downstream of the nozzle exits. Detailed measurements of heat transfer and pressure were made both ahead and downstream of the injection station, with the greatest concentration of measurements in the regions of shock-wave/boundary layer interaction. The major objectives of these experimental studies were to explore the effectiveness of film cooling in the presence of regions of shock-wave/boundary layer interaction and, more specifically, to determine how boundary layer separation and the large recompression heating rates were modified by film cooling. Detailed distributions of heat transfer and pressure were obtained in the incident-shock/wall-jet interaction region for a series of shock strengths and impingement positions for each of the two nozzle heights. Measurements were also made to examine the effects of nozzle lip thickness on cooling effectiveness. The major conclusion from these studies was that the effect of the cooling film could be readily dispersed by relatively weak incident shocks, so the peak heating in the recompression region was not significantly reduced by even the largest levels of film cooling. For the case studies in the absence of film cooling, the interaction regions were unseparated. However, adding film cooling resulted in regions of boundary layer separation induced in the film cooling layer, the size of which regions first increased and then decreased with increased film cooling. Surprisingly, the size of the separated regions and the magnitude of the recompression heating were not strongly influenced by the thickness of the cooling film, nor by the point of shock impingement relative to the exit plane of the nozzles. The lip thickness was found to have little effect on cooling effectiveness. Measurements with and in the absence of shock interaction were compared with the results of earlier experimental studies and correlated in terms of the major parameters controlling these flows.

Holden, Michael S.↗

DOE OSTI2024

Probabilistic Analysis of Long-Term Degradation of Microwave Cavity Flow Sensor

We are investigating a microwave resonant cavity transducer for flow sensing in the vessel of a high temperature fluid advanced reactor (AR), such as a molten salt cooled reactor (MSCR) or a sodium fast reactor (SFR). This transducer is a hollow metallic cylindrical cavity, with the flat wall of the cylinder flexible enough to undergo microscopic deflection due to dynamic fluid pressure. Membrane deflection leads to a shift in the resonant frequency, which can be detected with a spectrum analyzer. We have performed a proof-of-concept experiment of flow sensing with the transducer in liquid sodium at 340°C in impinging liquid jet geometry. The transducer remained in liquid sodium for 70 days. After removal, no structural damage was observed, and the expected transducer response was verified in a water test. Because long-term (multi-year) experimental tests of transducer resilience to harsh environment are not practical, we have developed a probabilistic model of creep to estimate transducer resilience to the harsh environment. The probabilistic model considers diffusion creep under the condition of high temperature and low stress, where the stress and temperature are allowed to be random variables with Gaussian distributions. Using the probabilistic model, we estimate inelastic membrane deflections due to creep for several temperature ranges. We conclude that for temperatures less than 650°C, creep has negligible long-term effect on the transducer performance. Since a yellowish residue was observed on the transducer surface after 70 days of immersion in liquid sodium, we have investigated possible evidence of corrosion. Chromium depletion is a typical indicator of the corrosion process in stainless steel. Scraping off a residue from the transducer and performing scanning electron microscopy (SEM) with energy dispersive analysis (EDS) did not find any chromium in the residue. Approximately 60% of the residue consisted of copper, which can be attributed to contamination of sodium due to powder residue from machining of copper and brass components of the transducer.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗