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At least 595 records · Page 33

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Measurement of waves in flows across a surface

A method and apparatus is disclosed for sensing wave flow across a surface wherein at least two pressure levels are sensed and combined to provide a representation of waves within the flow. In the preferred embodiment holes bored through the aircraft surface at an interval of one-half the wavelength of the flow being measured introduce pressure perturbations into a cavity so they may acoustically interfere. The interfering waveform is sensed by at least one microphone disposed in the cavity.

Kendall, James M., Jr.↗

NASA NTRS2003

Investigations of Mechanisms Associated with Nucleate Boiling Under Microgravity Conditions

In this work a building block type of approach is used so that a basic understanding of the processes that contribute to nucleate boiling heat fluxes under microgravity conditions can be developed. This understanding will lead to development of a mechanistic model for nucleate boiling heat transfer which could eventually be used as a design tool in space applications. Task Description Task 1: Fabrication of the Experimental Setup. Under this task, the test section and liquid holding and viewing chambers will be fabricated. Artificial cylinder cavities will be formed on silicon wafers. A single cavity and two or four cavities, with a prescribed spacing and size, will be formed. The desired nucleation wall superheat will be used to determine the size of the mouth of the cavities. Task 2: Experiments. The basic experiments for flow and temperature field around single and multiple (2 or 4 separated or merged bubbles growing on downward facing or inclined surfaces) will be carried out under normal gravity conditions. The experiments will be conducted at one atmosphere pressure, but liquid subcooling will be varied from 0 to 30C. Water and PF-5050 will be used as test liquids. Task 3: Analytical/Numerical Models. In this task, transient temperature and flow field in vapor and liquid will be determined during growth of a single bubble. Analysis will include the evolution of the vapor-liquid interface and development of microlayer underneath the bubbles. For merged bubbles, detailed calculations of flow and temperature field will be carried out for transient shapes of vapor stems supporting a large bubble and the corresponding evaporation rate. Flow and temperature field for a bubble sliding along a heated wall will also be determined. Microgravity conditions will be simulated and a framework of a numerical tool for prediction of nucleate boiling heat fluxes under microgravity conditions will be developed. Task 4: Experiments in a KC-135. To understand bubble growth and detachment behavior of single or large merged bubbles, boiling experiments will be conducted under low gravity (10-2 g) conditions of the aircraft. In these experiments, 'designed' surfaces will be used. Visual observations and heat transfer data will be taken, but holography will not be used. The apparatus used for laboratory experiments will also be employed for experiments in the aircraft. Task 5: Experiments in the Space Shuttle. Effort will be devoted for defining a boiling experiment to be conducted on a 'designed' surface. The experiment will provide microgravity data on bubble growth and departure. These data are needed for development of a credible model for nucleate boiling heat fluxes under microgravity conditions. The heat transfer data will also be obtained and will be used to validate the models.

Dhir, Vijay K.↗

NASA NTRS2003

Optical and Probe Diagnostics Applied to Reacting Flows

We plan to explore three major threads during the fellowship period. The first interrogates the flame synthesis of carbon nanotubes using aerosol catalysts. Laser light scattering will reveal changes in particle size at various heights above the burner. Analysis of the flame gas by mass spectroscopy will reveal the chemical composition of the mixture. Finally, absorption measurements will map the nanotube concentration within the flow. The second thread explores soot oxidation kinetics. Cavity ring-down absorption measurements of the carbonaceous aerosol can provide a measure of the mass concentration with time and, hence, an oxidation rate. Spectroscopic and direct probe measurements will provide the temperature of the system needed for subsequent modeling. The third thread will explore the details of turbulent flame dynamics. Laser induced incandescence will be applied to measurements of soot volume fraction in a 2-d configuration. Analysis of seed tracer particles by planar laser light MIE scattering will reveal the elemental fuel mixture fraction in the flames. Cavity ring-down spectroscopy, a pulsed transient absorption method, will determine the instantaneous mass loading and its fluctuation. Finally, fluorescence measurements will investigate the formation of PAH's in these flames.

Ticich, Thomas M.↗

NASA NTRS1992

Measurement of waves in flows across a surface

A method and apparatus for sensing wave flow across a surface wherein at least two pressure levels are sensed and combined to provide a representation of waves within the flow. In the preferred embodiment holes bored through the aircraft surface at an interval of one-half the wavelength of the flow being measured introduce pressure perturbations into a cavity so they may acoustically interfere. The interfering waveform is sensed by at least one microphone disposed in the cavity.

Kendall, Jr., James M.↗

NASA NTRS1991

Power turbine ventilation system

Air control mechanism within a power turbine section of a gas turbine engine. The power turbine section includes a rotor and at least one variable pitch propulsor blade. The propulsor blade is coupled to and extends radially outwardly of the rotor. A first annular fairing is rotatable with the propulsor blade and interposed between the propulsor blade and the rotor. A second fairing is located longitudinally adjacent to the first fairing. The first fairing and the second fairing are differentially rotatable. The air control mechanism includes a platform fixedly coupled to a radially inner end of the propulsor blade. The platform is generally positioned in a first opening and a first fairing. The platform and the first fairing define an outer space. In a first position corresponding with a first propulsor blade pitch, the platform is substantially conformal with the first fairing. In a second position corresponding with the second propulsor blade pitch, an edge portion of the platform is displaced radially outwardly from the first fairing. When the blades are in the second position and rotating about the engine axis, the displacement of the edge portion with respect to the first fairing allows air to flow from the outer space to the annular cavity.

Wakeman, Thomas G.↗

DOE OSTI2021

Modeling of HTTF test PG-26 using RELAP5-3D and SAM

The High Temperature Test Facility (HTTF) at Oregon State University (OSU) is a scaled integral effects experiment designed to investigate transient behavior in high-temperature gas-cooled nuclear reactors (HTGR) with prismatic fuel and reflector blocks [1]. Several tests have been completed at the HTTF including depressurized conduction cooldown (DCC) and pressurized conduction cooldown (PCC) transients. This summary reports on the analysis of test PG-26 using the INL system code REALP5-3D [2] as well as the ANL system code SAM [3]. Test PG-26 is a progression of the Double Ended Inlet-Outlet Crossover Duct Break transient that is referred to as a DCC [4]. Core initial conditions (i.e., before the DCC started) have been met using low power (<100 kW) and two of ten available electric heater banks. The DCC transient was initiated during the 50th hour of the test. The break valves were opened, and hot helium from the core and cold helium from the reactor cavity simulation tank (RCST) started mixing. The gases flowed in a countercurrent fashion, where the top half of the hot duct contained hot helium that flowed in one direction and cold helium that flowed in the other direction in the bottom half of the duct. After the pressure and density reached equilibrium, the event entered a diffusion mode. The onset of a reverse natural circulation was not observed during the DCC period of the test.

97 MATHEMATICS AND COMPUTING↗

NASA NTRSDate not supplied

Simulations of the Modular Axisymmetric Scramjet Test Rig Under Reacting Flow Conditions

Simulations of the Air Force Research Laboratory (AFRL) Modular Axisymmetric Scramjet Test Rig (MASTeR) are presented. MASTeR is a parametric test article capable of investigating various scramjet cavity flameholder designs and fueling strategies with the goal to characterize and optimize flameholding capability. In the current work, three cavity aspect ratios, three depths, and two fueling strategies (upstream and in-cavity) with ethylene at a nominal facility pressure and temperature conditions are evaluated. The simulations are performed for mixing-only and reacting flows, and the resulting flow characteristics are compared. For each configuration and fueling strategy, cavity residence time, entrainment rate, and fuel-air equivalence ratio are computed. The MASTeR geometry is defined in the Engineering Sketch Pad (ESP) and the simulations use a sketch-to-solution (S2S) automated unstructured grid adaptation tool in VULCAN-CFD. This tool automatically generates a simulation grid from the ESP geometry and systematically adapts it to the numerical solution based on the Hessian error estimate of a specified flow field parameter. Reynolds averaged simulations (RAS) are used with typical two-equation linear eddy viscosity and diffusivity model. The resulting database can be compared with the experimental data as those becomes available and explored to develop models for cavity performance for scramjet propulsion design applications.

hypersonics↗

NASA NTRS2001

Studies of Elementary Reactions of Chemical Importance in the Atmospheres of Planets

The methyl self-reaction was studied at T = 298 K and 202 K and at three different pressures, P = 0.5, 1.0, and 2.1 Torr. The experimental measurements were performed in our discharge flow-mass spectrometer (DF-MS) apparatus. The methyl radicals were generated by the reaction of F with methane. Passing a mixture of molecular fluorine, F2, in helium through a microwave cavity generated the atomic fluorine reagent. The atomic F enters the flow tube through a rear port on the flow tube. The methane reagent enters the flow tube through a movable injector located coaxial in the flow tube. The decay of methyl radical signal was monitored at a mass/charge ratio (m/z) of 15 as a function of the injector distance. To minimize secondary chemistry from the reaction CH3 + F to CH2 + HF the initial [CH4](sub 0)/[F](sub 0) was above 37.0 and typically 100. This ensures a 1:1 relationship between initial [F] and [CH3]. A titration of F with excess Cl2 yields the initial [F](sub 0). Our experimental methodology to accurately measure the mass spectrometer scaling factor, i.e., the relationship between initial signal and [CH3](sub 0) has been improved. Now we measure the CH3 signal decay under exponential decay conditions at low initial [F](sub 0), 3x10(exp 11) molecule/cc, in the presence of Cl2. This minimizes the second-order decay contributed by the CH3 self-reaction and a simple extrapolation of the 1n(signal) vs time plot to t = 0 gives the initial signal. This provides the desired relationship between initial signal at 15 amu and [CH3](sub 0). The resulting calibration is then applied to the observed decay of the CH3 signal at high concentrations of CH3 assuming linearity of this scaling factor.

Nesbitt, Fred L.↗

NASA NTRS1985

A theoretical study of non-adiabatic surface effects for a model in the NTF cryogenic wind tunnel

A theoretical analysis was made of the severity and effect of nonadiabatic surface conditions for a model in the NTF cryogenic wind tunnel. The nonadiabatic condition arises from heaters that are used to maintain a constant thermal environment for instrumentation internal to the model. The analysis was made for several axi-symmetric representations of a fuselage cavity, using a finite element heat conduction code. Potential flow and boundary layer codes were used to calculate the convection condition for the exterior surface of the model. The results of the steady state analysis show that it is possible to maintain the surface temperature very near the adiabatic value, with the judicious use of insulating material. Even for the most severe nonadiabatic condition studied, the effects on skin friction drag and displacement thickness were only marginally significant. The thermal analysis also provided an estimate of the power required to maintain a specified cavity temperature.

Macha, J. M.↗

NASA NTRS1959

Exploratory Study of Ventilated Flows About Yawed Surface-Piercing Struts

Reported herein are the results of observations and measurements made in connection with a study of the phenomenon of the development of atmosphere-connected cavities about surface-piercing struts. Conditions for the existence of such ventilated flows which have been derived from the experimental data are presented. In addition, certain broad conclusions pertinent to model testing and full-scale design are reached. Further experimentation to define the inception of ventilation as a function of boundary-layer state or Reynolds number is required.

Breslin, John P.↗

NASA NTRS2006

Three-Dimensional Computational Model for Flow in an Over-Expanded Nozzle With Porous Surfaces

A three-Dimensional computational model is used to simulate flow in a non-axisymmetric, convergent-divergent nozzle incorporating porous cavities for shock-boundary layer interaction control. The nozzle has an expansion ratio (exit area/throat area) of 1.797 and a design nozzle pressure ratio of 8.78. Flow fields for the baseline nozzle (no porosity) and for the nozzle with porous surfaces of 10% openness are computed for Nozzle Pressure Ratio (NPR) varying from 1.29 to 9.54. The three dimensional computational results indicate that baseline (no porosity) nozzle performance is dominated by unstable, shock-induced, boundary-layer separation at over-expanded conditions. For NPR less than or equal to 1.8, the separation is three dimensional, somewhat unsteady, and confined to a bubble (with partial reattachment over the nozzle flap). For NPR greater than or equal to 2.0, separation is steady and fully detached, and becomes more two dimensional as NPR increased. Numerical simulation of porous configurations indicates that a porous patch is capable of controlling off design separation in the nozzle by either alleviating separation or by encouraging stable separation of the exhaust flow. In the present paper, computational simulation results, wall centerline pressure, mach contours, and thrust efficiency ratio are presented, discussed and compared with experimental data. Results indicate that comparisons are in good agreement with experimental data. The three-dimensional simulation improves the comparisons for over-expanded flow conditions as compared with two-dimensional assumptions.

Abdol-Hamid, K. S.↗

NASA NTRS1987

A preliminary study of extended magnetic field structures in the ionosphere

Several plasma phenomena which are to be expected around a magnet in LEO were identified and analyzed qualitatively. The ASTROMAG cusp magnet will create an extended field whose strength drops to the ambient level over a scale length of approx. 15 m; the combined field has a complex topology with ring nulls and open and closed field lines. The entire configuration is moving through the partially ionized F-layer of the ionosphere at a speed slow compared to the local Alfven speed but fast compared to the ion sound speed. The ambient plasma crosses the extended field structure in a time short compared to the ion Larmor period yet long relative to the electron Larmor period. Thus, electrons behave as a magnetized fluid while ions move ballistically until reflected from higher fields near the cusp. Since the Debye length is short compared to the field scale length, an electrostatic shock-like structure forms to equilibrate the flows and achieve quasi-neutrality. The ambient plasma will be excluded from a cavity near the magnet. The size and nature of the strong interaction region in which the magnet significantly perturbs the ambient flow were determined by studying ion orbits numerically. Lecture viewgraphs summarizing these results are presented.

Sullivan, James D.↗

NASA NTRS2003

Computational Study of Fluidic Thrust Vectoring using Separation Control in a Nozzle

A computational investigation of a two- dimensional nozzle was completed to assess the use of fluidic injection to manipulate flow separation and cause thrust vectoring of the primary jet thrust. The nozzle was designed with a recessed cavity to enhance the throat shifting method of fluidic thrust vectoring. The structured-grid, computational fluid dynamics code PAB3D was used to guide the design and analyze over 60 configurations. Nozzle design variables included cavity convergence angle, cavity length, fluidic injection angle, upstream minimum height, aft deck angle, and aft deck shape. All simulations were computed with a static freestream Mach number of 0.05. a nozzle pressure ratio of 3.858, and a fluidic injection flow rate equal to 6 percent of the primary flow rate. Results indicate that the recessed cavity enhances the throat shifting method of fluidic thrust vectoring and allows for greater thrust-vector angles without compromising thrust efficiency.

Deere, Karen↗

DOE OSTI2022

Thermal-Hydraulics Modeling and Simulations of Hot Pool Using the SAS-CFD Coupled Code

The main goal of this activity is to test the dynamic coupling of the SAS4A/SASSYS-1 (SAS) and CFD models, using a recently patched version of the SAS code intended to address an undocumented limitation that hindered the Versatile Test Reactor (VTR) simulation efforts in FY21. As described in previous VTR calculation reports, the undocumented limitation in SAS v5.4 does not allow the user to activate the CFD coupling option during restart calculations. Since the analysts were unaware of this limitation, prior SAS-CFD simulation results for the protected station blackout (PSBO) transient were erroneous. Root-cause analysis was performed to determine the cause of this undocumented limitation in SAS v5.4, the SAS software was updated in a new patch, and the SAS-CFD simulations were repeated with this patched software. The results of the SAS-CFD simulations documented in this report show that the software patch does address the cited issue, and that the patched software indeed supports the activation of the CFD coupling model in restart calculations. The SAS development team will determine the schedule for implementing the patch in an official software release. This report documents updated SAS-CFD simulations of the PSBO transient response in the VTR. The hot pool is modeled with the CFD code STAR-CCM+, which is coupled at the flow boundaries to the SAS model of the primary heat transport system. SAS computes the mass flow rate and temperature at each core subassembly outlet, the thermal insulation cavity bypass, and the IHX inlet windows. CFD in turn computes the absolute pressure and temperature at each of these boundaries. The SAS code will ignore the temperature data at flow boundaries where flow is directed into the hot pool, i.e., at the core subassembly outlets unless flow reversal occurs. Similarly, CFD will ignore temperature data at boundaries where the flow is directed out of the hot pool, i.e., at the IHX inlets except under flow reversal. The focus of this work is to ensure that the SAS software patch addresses the undocumented limitation described in prior VTR calculation reports, rather than the accurate assessment of thermal stratification in the VTR during protected transients. This motivates the development of a new, simplified CFD model with a coarser mesh to accelerate the testing process. The updated model, and simplifying assumptions, are documented in this report. In future work, the thermal stratification assessment should be performed in more detail. The simplified CFD model can be improved by performing grid convergence studies sensitivity studies of turbulence parameters (e.g., Prandtl number, turbulence production and dissipation parameters) on temperature distributions and thermal stratification.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRSDate not supplied

Assessment of Acoustic Behavior for Perforate-Over-Large-Cell Liners

This study explores the effects of increasing the cell size for large-cell acoustic liners. Tests are conducted in the NASA Langley Grazing Flow Impedance Tube to evaluate liners with increasingly larger cell dimensions (up to 2” x 4” cross-section). Conventional impedance eduction confirms that liners with 2” x 3” cells (or larger) must be evaluated using nonlocally reacting assumptions. In addition, due to the sound propagation within cavities, the liners must be modeled using higher fidelity techniques. Thus, grazing flow duct and acoustic liner are modeled simultaneously using finite element methods. The facesheet is modeled using a transfer impedance, while the rest of the domain is modeled using the convected Helmholtz equation. The acoustic pressures predicted are shown to compare favorably with those measured in the Grazing Flow Impedance Tube.

large diameter↗

NASA NTRS2005

Numerical Investigation of Flow in an Over-Expanded Nozzle with Porous Surfaces

A new porous condition has been implemented in the PAB3D solver for simulating the flow over porous surfaces. The newly-added boundary condition is utilized to compute the flow field of a non-axisymmetric, convergent-divergent nozzle incorporating porous cavities for shock-boundary layer interaction control. The nozzle has an expansion ratio (exit area/throat area) of 1.797 and a design nozzle pressure ratio of 8.78. The flow fields for a baseline nozzle (no porosity) and for a nozzle with porous surfaces (10% porosity ratio) are computed for NPR varying from 2.01 to 9.54. Computational model results indicate that the over-expanded nozzle flow was dominated by shock-induced boundary-layer separation. Porous configurations were capable of controlling off-design separation in the nozzle by encouraging stable separation of the exhaust flow. Computational simulation results, wall centerline pressure, mach contours, and thrust efficiency ratio are presented and discussed. Computed results are in excellent agreement with experimental data.

Elmiligui, Alaa↗

NASA NTRS2006

Numerical Investigation of Flow in an Over-expanded Nozzle with Porous Surfaces

A new porous condition has been implemented in the PAB3D solver for simulating the flow over porous surfaces. The newly-added boundary condition is utilized to compute the flow field of a non-axisymmetric, convergent-divergent nozzle incorporating porous cavities for shock-boundary layer interaction control. The nozzle has an expansion ratio (exit area/throat area) of 1.797 and a design nozzle pressure ratio of 8.78. The flow fields for a baseline nozzle (no porosity) and for a nozzle with porous surfaces (10% porosity ratio) are computed for NPR varying from 2.01 to 9.54. Computational model results indicate that the over-expanded nozzle flow is dominated by shock-induced boundary-layer separation. Porous configurations are capable of controlling off-design separation in the nozzle by encouraging stable separation of the exhaust flow. Computational simulation results, wall centerline pressure, mach contours, and thrust efficiency ratio are presented and discussed. Computed results are in excellent agreement with experimental data.

Abdol-Hamid, Khaled S.↗

NASA NTRS1982

Correlation of the effects of grazing flow on the impedance of Helmholtz resonators

Measurements of the acoustic impedance of a two-dimensional Helmholtz resonator, i.e., a cavity coupled to the environment through a high-aspect ratio slot are presented as a function of the velocity of a steady flow above the orifice of the resonator. The structure of the unsteady flow above the orifice is outlined from hot-wire measurements. A simplified model of it is proposed and analyzed, leading to a successful correlation of both the resistance and the reactance of the resonator.

Walker, B. E.↗