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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Effect of ratio of wall boundary layer thickness to jet diameter on mixing of a normal hydrogen jet in a supersonic stream

A preliminary experimental program was conducted to determine the effect of the ratio of the free-stream boundary-layer thickness to jet diameter on the secondary jet penetration and mixing rate. Tests were conducted on a flat plate in a Mach number 4.05 airflow with sonic injection of hydrogen normal to the free-stream direction from circular underexpanded injectors. The ratio of boundary-layer thickness to jet diameter ranged from 1.25 to 6.5. Previous correlations of mixing performance were modified to account for the effect of the ratio of boundary-layer thickness to jet diameter.

Mcclinton, C. R.↗
NASA NTRS1993

Study and modeling of finite rate chemistry effects in turbulent non-premixed flames

The development of numerical models that reflect some of the most important features of turbulent reacting flows requires information about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between turbulent and chemical processes is so strong that it is extremely difficult to isolate the role played by one individual physical phenomenon. Direct numerical simulation (hereafter DNS) allows us to study in detail the turbulence-chemistry interaction in some restricted but completely defined situations. Globally, non-premixed flames are controlled by two limiting regimes: the fast chemistry case, where the turbulent flame can be pictured as a random distribution of local chemical equilibrium problems; and the slow chemistry case, where the chemistry integrates in time the turbulent fluctuations. The Damkoehler number, ratio of a mechanical time scale to chemical time scale, is used to distinguish between these regimes. Today most of the industrial computer codes are able to perform predictions in the hypothesis of local equilibrium chemistry using a presumed shape for the probability density function (pdt) of the conserved scalar. However, the finite rate chemistry situation is of great interest because industrial burners usually generate regimes in which, at some points, the flame is undergoing local extinction or at least non-equilibrium situations. Moreover, this variety of situations strongly influences the production of pollutants. To quantify finite rate chemistry effect, the interaction between a non-premixed flame and a free decaying turbulence is studied using DNS. The attention is focused on the dynamic of extinction, and an attempt is made to quantify the effect of the reaction on the small scale mixing process. The unequal diffusivity effect is also addressed. Finally, a simple turbulent combustion model based on the DNS observations and tractable in real flow configurations is proposed.

Vervisch, Luc↗
NASA NTRS1972

Turbulent mixing film cooling correlation

Film cooling effectiveness correlation predicts air flow requirement for cooling gas turbine combustors. Turbulent mixing model accounts for mixing rate between cooling film and hot gas stream. Resulting equation correlates data within plus or minus 20 percent.

Juhasz, A. J.↗
NASA NTRS1994

Effect of chemical heat release in a temporally evolving mixing layer

Two-dimensional numerical simulations of a temporally evolving mixing layer with an exothermic infinitely fast diffusion flame between two unmixed reactants have been carried out in the limit of zero Mach number to study the effect of the heat release on the early stages of the evolution of the flow. Attention has been directed to relatively large values of the oxidizer-to-fuel mass stoichiometric ratio typical of hydrocarbon flames, and initial vorticity distributions thicker than the temperature and species distributions have been chosen to mimic the situation at the outlet of a jet. The results show that, during the stages of the evolution covered by the present simulations, enhancement of combustion occurs by local stretching of the flame without much augmentation of its area. The rate of product generation depends strongly on the initial conditions, which suggests the possibility of controlling the combustion by acting on the flow. Rollup and vortex amalgamation still occur in these reacting flows but are very much affected by the production of new vorticity by baroclinic torques. These torques lead to counter rotating vortex pairs around the flame and, more importantly, in thin layers of light fluid that leave the vicinity of the flame when the Kelvin-Helmholtz instability begins to develop. Propelled by the vortex pairs, these layers wind around, split on reaching high pressure regions, and originate new vortex pairs in a process that ends up building large-scale vortices with a vorticity distribution more complex than for a constant density fluid.

Higuera, F. J.↗
NASA NTRS1999

Supersonic Jet Mixing Enhancement due to Natural and Induced Screech

Outline of presentation are: (1) Review of experimental apparatus. (2) Effect of natural screech of jet mixing; converging nozzle, underexpanded jet and converging-diverging nozzle, design pressure.(3) Effect of induced screech on jet mixing: produced by paddles in shear layers, similar to edge tones, and converging-diverging nozzle, design pressure. (4) Effect of paddles on near-field jet noise. and (5) Concluding remarks.

Rice, E. J.↗
NASA NTRS1992

Mixed convective-dynamic roll vortices and their effects on initial wind and temperature profiles

A new nonlinear 14-coefficient spectral model of two-dimensional shallow Boussinesq flow is developed and used to investigate the onset and development of both dynamically and convectively forced boundary-layer rolls. The model is developed to accept arbitrary basic-state wind profiles as dynamic forcing, using an Ekman profile to provide a means for easy comparison with other studies. The results are qualitatively compared with those of previous theoretical and observational investigations. The rolls are shown to significantly alter the initial wind profile in the sense found by Faller and Kaylor (1967) and Brown (1970), but via a mechanism independent of the Coriolis force.

Haack, Tracy↗
NASA NTRS1996

Effect of a delta tab on fine scale mixing in a turbulent two-stream shear layer

The fine scale mixing produced by a delta tab in a shear layer has been studied experimentally. The tab was placed at the trailing edge of a splitter plate which produced a turbulent two-stream mixing layer. The tab apex tilted downstream and into the high speed stream. Hot-wire measurements in the 3-D space behind the tab detailed the three velocity components as well as the small scale population distributions. These small scale eddies, which represent the peak in the dissipation spectrum, were identified and counted using the Peak-Valley-Counting technique. It was found that the small scale populations were greater in the shear region behind the tab, with the greatest increase occurring where the shear layer underwent a sharp turn. This location was near, but not coincident, with the core of the streamwise vortex, and away from the region exhibiting maximum turbulence intensity. Moreover, the tab increased the most probably frequency and strain rate of the small scales. It made the small scales smaller and more energetic.

Foss, J. K.↗
NASA NTRS2016

Mixing the Solar Wind Proton and Electron Scales: Effects of Electron Temperature Anisotropy on the Oblique Proton Firehose Instability

The double adiabatic expansion of the nearly collisionless solar wind plasma creates conditions for the firehose instability to develop and efficiently prevent the further increase of the plasma temperature in the direction parallel to the interplanetary magnetic field. The conditions imposed by the firehose instability have been extensively studied using idealized approaches that ignore the mutual effects of electrons and protons. Recently, more realistic approaches have been proposed that take into account the interplay between electrons and protons, unveiling new regimes of the parallel oscillatory modes. However, for oblique wave propagation the instability develops distinct branches that grow much faster and may therefore be more efficient than the parallel firehose instability in constraining the temperature anisotropy of the plasma particles. This paper reports for the first time on the effects of electron plasma properties on the oblique proton firehose (PFH) instability and provides a comprehensive vision of the entire unstable wave-vector spectrum, unifying the proton and the smaller electron scales. The plasma β and temperature anisotropy regimes considered here are specific for the solar wind and magnetospheric conditions, and enable the electrons and protons to interact via the excited electromagnetic fluctuations. For the selected parameters, simultaneous electron and PFH instabilities can be observed with a dispersion spectrum of the electron firehose (EFH) extending toward the proton scales. Growth rates of the PFH instability are markedly boosted by the anisotropic electrons, especially in the oblique direction where the EFH growth rates are orders of magnitude higher.

plasmas↗
NASA NTRS1990

Injectant mole fraction measurements of transverse injection in constant area supersonic ducts

Planar measurements of the injectant mole fraction distribution in a nonreacting model SCRAMJET combustor have been made using a nonintrusive optical technique, laser-induced iodine fluorescence. The combustor geometry investigated in this work was staged, transverse sonic injection of air into Mach 2 and Mach 2.9 freestreams. Accurate three-dimensional surveys of the injectant mole fraction distribution for both freestream Mach numbers have been generated. These experimental measurements provide valuable insight into the fluid mechanics of the mixing process. The existence of streamwise vortices is shown to dominate the mixing in the injector nearfield while shock wave interactions with the injectant plume are seen to significantly enhance mixing downstream of the injectors. The effect of combustor Mach number on injectant mixing is found to be small for this geometry. These measurements provide an accurate data set for the validation of computational fluid dynamics codes being developed for the calculation of highly three-dimensional nonreacting supersonic combustor flow fields.

Hollo, Steven D.↗
NASA NTRS1992

Spanwise averaging of plane mixing layer properties

An attempt is made to demonstrate the effects of streamwise vorticity on such mixing layer global properties as layer thickness and peak Reynolds stresses. Attention is given to differences between results obtained from spanwise averaging over a number of velocity profiles and those given by the more conventional approach of analyzing a single profile measured along the test section centerline. It is found that the growth rate and streamwise development of peak Reynolds stresses in the near field can be significantly affected by spanwise variations in the mixing layer.

Bell, James H.↗
NASA NTRS1987

Space Bioreactor Science Workshop

The first space bioreactor has been designed for microprocessor control, no gaseous headspace, circulation and resupply of culture medium, and a slow mixing in very low shear regimes. Various ground based bioreactors are being used to test reactor vessel design, on-line sensors, effects of shear, nutrient supply, and waste removal from continuous culture of human cells attached to microcarriers. The small (500 ml) bioreactor is being constructed for flight experiments in the Shuttle middeck to verify systems operation under microgravity conditions and to measure the efficiencies of mass transport, gas transfer, oxygen consumption, and control of low shear stress on cells. Applications of microcarrier cultures, development of the first space bioreactor flight system, shear and mixing effects on cells, process control, and methods to monitor cell metabolism and nutrient requirements are among the topics covered.

Morrison, Dennis R.↗
NASA NTRS1971

Turbulent jet mixing in a supersonic stream

An experimental study of turbulent, subsonic, coaxial jet mixing of air in a supersonic air stream is presented. Data taken at five axial stations downstream of the exit of the jet supply tube, which was suspended through the nozzle throat of a supersonic wind tunnel, are given in the form of total pressure, Mach number, and velocity distributions. An investigation of the effect of swirl as a mixing aid was conducted. Swirl, produced by tangential injection of 50% of the total air mass flow leaving the jet supply tube, was examined through Schlieren photographs and total pressure surveys. From a comparison of nonswirl and swirl data, it is concluded that the swirl has no discernible effect on the mixing.

Swanson, R. C.↗
NASA NTRS1995

Supersonic coaxial jet noise predictions

Predictions are made for the noise radiation from supersonic, coaxial jets. These predictions are based on the assumption that the noise radiation in the downstream direction of supersonic jets is dominated by sound generated by instability waves with supersonic phase velocities relative to ambient. Since the analysis requires a known mean flow and the coaxial jet mean flow is not described easily in terms of analytical functions, a numerical prediction is made for its development. The compressible, Reynolds averaged, boundary layer equations are solved with a modified mixing length turbulence model. The model has been calibrated to account for compressibility and temperature effects on the rate of mixing. Both normal and inverted velocity profile jets are considered. Predictions are made for the differences between the noise radiated by coaxial jets with difference operating conditions and a single reference jet with the same thrust, mass flow, and exit area. The effects of area ratio changes and simulated enhanced mixing on noise radiation are also considered.

Dahl, Milo D.↗
NASA NTRS1992

Results of a preliminary investigation of inlet unstart on a high-speed civil transport airplane concept

The aircraft design engineer of today is tasked with satisfying an increasing number of conflicting requirements. The fact that conflict in these requirements may be technically, economically, or politically motivated usually compounds the difficulty of determining the best solution to a design issue. In this regard, propulsion/airframe integration for supersonic airplanes must rank as one of the most challenging aspects of airplane design. For the cruise Mach numbers currently being considered for High-Speed Civil Transport (HSCT) airplanes, the inlet requirements of low drag, low bleed flow, and high pressure recovery appear to be best met with a mixed-compression design. Unfortunately, these desirable attributes come with a highly undesirable companion: the inlet unstart phenomenon. Concern over the effects of a mixed-compression inlet unstart on the vehicle dynamics of large, high-speed aircraft is not new; a comprehensive wind-tunnel study addressing the problem was published in 1962. Additional investigations of the problem were made throughout the United States SST program and the follow-on NASA program into the late 1970's. The current study sought to examine the magnitude of the problem in order to determine if an inlet unstart posed a potential hazard severe enough to preclude the use of mixed-compression inlets on proposed HSCT concepts.

Domack, Christopher S.↗
NASA NTRS2008

Mixed Mode Fracture of Plasma Sprayed Thermal Barrier Coatings: Effects of Anisotropy and Heterogeneity

The combined mode I-mode II fracture behavior of anisotropic ZrO2-8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of KI/KII were also determined. The mixed-mode fracture behavior of the microsplat coating material was modeled using Finite Element approach to account for anisotropy and micro cracked structures, and predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

Zhu, Dongming↗
NASA NTRS1981

Analysis for predicting adiabatic wall temperatures with single hole coolant injection into a low speed crossflow

Assuming the local adiabatic wall temperature equals the local total temperature in a low speed coolant mixing layer, integral conservation equations with and without the boundary layer effects are formulated for the mixing layer downstream of a single coolant injection hole oriented at a 30 degree angle to the crossflow. These equations are solved numerically to determine the center line local adiabatic wall temperature and the effective coolant coverage area. Comparison of the numerical results with an existing film cooling experiment indicates that the present analysis permits a simplified but reasonably accurate prediction of the centerline effectiveness and coolant coverage area downstream of a single hole crossflow streamwise injection at 30 degree inclination angle.

Wang, C. R.↗