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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Time Accurate Simulation of Nonequilibrium Flow inside the NASA Ames Electric Arc Shock Tube

Numerical investigations of the ow field inside NASA Ames' Electric Arc Shock Tube have been performed. The focus is to simulate the experiments designed to reproduce shock layer radiation layer relevant to Earth re-entry conditions. This paper assess the current computational capability in simulating unsteady nonequilibrium flows in the presence of strong shock waves with state-of-the-art physical models. The technical approach is described with preliminary results presented for one specific ow condition. The numerical problems encountered during the computation of these flows are detailed, along with the methods used to resolve them. Post-shock conditions are discussed and compared to CEA equilibrium prediction.

Bensassi, Khalil↗
NASA NTRS1993

A sonic flow equation for electric arc jets

The relationship between total enthalpy and the flow parameters of two types of electric arc jets is discussed. A simple equation for the supersonic arc jet, based on ARCFLO code calculations for mass-average total enthalpy, is presented in terms of a sonic flow parameter. At enthalpies greater than about 25 MJ/kg, this equation shows better agreement with experimental arc jet data than a previous equation.

Shepard, Charles E.↗
NASA NTRS2019

Full Facility Shock Frame Simulations of the Electric Arc Shock Tube

Radiative heating computations are performed for high speed lunar return experiments conducted in the Electric Arc Shock Tube (EAST) facility at NASA Ames Research Center. The nonequilibrium radiative transport equations are solved via NASA's in-house radiation code NEQAIR using flow field input from US3D flow solver. The post-shock flow properties for the 10 km/s Earth entry conditions are computed using the stagnation line of a blunt-body and a full facility CFD (Computational Fluid Dynamics) simulation of the EAST shock tube. The shocked gas in the blunt-body flow achieves a thermochemical equilibrium away from the shock front whereas EAST flow exhibits a nonequilibrium behavior due to strong viscous dissipation of the shock by boundary layer. The full-tube flow calculations capture the influence of the boundary layer on the shocked gas state and provide a realistic fluid dynamic input for the radiative predictions. The integrated radiance behind the shock is calculated in NEQAIR for wavelength regimes from Vacuum-UltraViolet (VUV) to InfraRed (IR), which are pertinent to the emission characteristics of high enthalpy shock waves in air. These radiance profiles are validated against corresponding EAST shots. The full-tube simulations successfully predict a sharp radiance peak at the shock front which gets smeared in the test data due to the spatial resolution in the measurements. The full facility based radiance behind the shock shows a slightly better match with the test data in the VUV and Red spectral regions, as compared to that from a blunt-body based predictions. The UV radiance is very similar for both geometries and under-predicts the test behavior. The IR test data matches better with the blunt-body based predictions where the full-tube simulations show a significant over-prediction.

Radiation↗
NASA NTRS2018

Full Facility Shock Frame Simulations of the Electric Arc Shock Tube

Radiative heating computations are performed for a range of high speed Earth entry experiments conducted in the Electric Arc Shock Tube at NASA Ames. The nonequilibrium radiative transport equations are solved in NEQAIR using flow field variables from the full facility CFD simulations of the EAST shock tube performed by US3D ow solver. These physics-based flow calculations lead to a significantly different post-shock gas state and associated radiation field as compared to that based on a simplified but computationally inexpensive calculation for flow over a blunt-body with appropriate initial conditions. The radiation spectra and radiance profiles are computed for an extensive range of wavelengths, from deep VUV to IR, which are pertinent to the emission characteristics of high enthalpy shock waves in air. The radiation properties of the shocked gas are calculated both in the nonequilibrium region at the shock, and in the equilibrium region behind the shock. Numerical predictions are found to be consistent with the experimental observations.

Simulations↗
NASA NTRS2015

Meteor Entry Characterization in the Electric Arc Shock Tube

This poster summarizes potential test opportunities in Ames' EAST facility that would benefit studies of meteor and asteroid entry into Earth's atmosphere. The Electric Arc Shock Tube (EAST) facility produces high speed (up to Mach 50) shockwaves at prescribed velocities, densities and atmospheric compositions.

Cruden, B. A.↗
NASA NTRSDate not supplied

Backshell Radiative Heating and Shock Layer Kinetic Measurement in NASA’s Electric Arc Shock Tube Facility

A methodology for creating incident shocks with similarity to the backshell radiative heating environment on planetary probes is presented. Two test series were carried out in the Electric Arc Shock Tube (EAST) at NASA Ames to quantify the backshell environment for planned and executed missions entering the atmospheres of Mars and Titan. The comparison of measured radiance in the shock tube to predicted post shock radiation levels is used to quantify the uncertainty in the model. This model uncertainty may then be related back to the flight condition to assess the error in the flight heating prediction. Tests for Mars entry show the shock tube measurements to be bracketed between two kinetic models by 2-7%. This suggests an 8% error in predicting the measured heating cannot be attributed to radiation. Comparisons to planned Titan entry suggest a substantial overprediction of the backshell radiation, which suggests opportunity for future refinement of radiative heating models.

radiation↗
NASA NTRSDate not supplied

Characterization of Titan Entry Radiative Heating in the Low Density Electric Arc Shock Tube

Prediction of aftbody radiative heating for Dragonfly’s entry at Titan requires accurate models to inform the design of its thermal protection systems. Previously reported investigations of shock layer aftbody radiation in the Electric Arc Shock Tube (EAST) at NASA Ames Research Center focused on the lower altitude/higher density part of the trajectory. This paper presents the first optical emission spectroscopy measurements of an ongoing test series in the new aluminum Low Density Shock Tube (LDST), recently installed at EAST, focusing on the radiative heating characterization through the higher altitude portion of Dragonfly’s entry path. Experimental data collected at a fill pressure of 0.1 Torr and shock velocities between 5.2 and 6.2 km/s show favorable agreement to similar conditions previously tested in the 4" High-Velocity Shock Tube, as well as improvements in the signal to noise ratio and available test time. Simulations employing DPLR and NEQAIR underpredict the experimental radiance, with increasing discrepancy from the NIR towards the UV wavelength range, thus motivating further efforts in improving the current non-Boltzmann model for the CN molecule.

A Fagnani↗
NASA NTRS1970

A stabilized low-frequency alternating-current electric arc

Establishing an arc between water-cooled tungsten-tipped electrodes, maintaining the arc along the centerline of a central jet of argon gas, and surrounding the argon jet with a coaxial sheath of nitrogen stabilizes operation of a low-frequency ac electric arc.

Lanzo, C. D.↗
NASA NTRSDate not supplied

Characterizing Electrical Arc Behavior in Ion Engines

Gridded ion engines represent a class of electric thrusters characterized by high propulsive efficiency and high total impulse capabilities. These engines operate by applying high voltage to multi-aperture electrodes, thereby electrostatically accelerating plasma to generate thrust. Within the course of normal operations, periodic occurrences of high voltage breakdowns manifest within the thruster. These breakdowns constitute an inherent aspect of operation, with observations indicating a diminishing frequency and total count over the thruster's operational lifespan. To safeguard the propulsion system during such occurrences, the power processing unit (PPU) employs an automated arc extinction sequence, termed "recycle," which is triggered upon detection of an over-current condition. The initial phase of this sequence involves momentarily deactivating the high voltage and reducing the discharge current to a predetermined level, minimizing plasma impingement as the ion beam is defocused. The high voltage is subsequently reapplied, and the discharge current is returned to its nominal value. The entire sequence typically spans approximately 800 milliseconds. Throughout a recycle event, the propulsion system experiences various current and voltage transients as the arc current traverses the system and different power supplies are toggled on and off.

electric propulsion↗
NASA NTRS2019

High temperature electric arc furnace and method

An apparatus and process for improving the microstructure of electrically conducting materials is disclosed by the present invention. A revolving heat source applies heat to the surface of the material evenly and quickly. One or more heat sinks quickly cool the material. In the preferred embodiment, the cooling may be done in such a way as to promote as high a degree of directional grain growth as desired or completely nondirectional grain growth.

Richard M Poorman↗
NASA NTRSDate not supplied

Characterizing Electrical Arc Behavior in Ion Engines

Test results using an engineering model Advanced NEXT thruster are presented to identify different arc types utilizing ground test hardware. Three distinct arc types were observed: grid-to-grid arcs, high voltage-to-chassis arcs, and a combination of both. The frequency of high voltage-to-chassis arcs ranged from 4-30%, depending on operating conditions and hardware configuration. Higher beam currents were typically associated with more frequent high voltage-to-chassis arcs. During these arcs, the measured chassis current levels ranged from 20-70 A, however a significant portion of the output beam current returned to the beam supply via the neutralizer cathode plasma, which may be a ground test facility effect. The paper also discusses conducted susceptibility tests that can be performed at the spacecraft level to address the transients associated with arcing events.

electric propulsion↗
NASA NTRS1976

Description and operating performance of a parallel-rail electric-arc system with helium driver gas for the Langley 6-inch expansion tube

A parallel-rail arc-discharge system to heat and pressurize the initial helium driver gas of the Langley 6-inch expansion tube is described. This system was designed for a 2.44-m-long driver vessel rated at 138 MPa, with a distance between rails of 20.3 cm. Electric energy was obtained from a capacitor storage system rated at 12,000 V with a maximum energy of 5 MJ. Tests were performed over a range of energy from 1.74 MJ to the maximum value. The operating experience and system performance are discussed, along with results from a limited number of expansion-tube tests with air and carbon dioxide as test gases.

Moore, J. A.↗