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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 109 records · Page 6

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NASA NTRS1989

Modeling of a pulsed fluid column and coupled piping with structural finite elements

Structural finite elements have been used to model the coupled fluidic-structural response of a liquid oxygen (LOX) feedline at a rocket engine test facility. The model simulates the effects of Pogo pulsing, a test procedure which uses a piston in a side branch to impart an oscillatory pressure pulse to the LOX column as it feeds the engine. In addition to the feedline's structural characteristics, the model accounts for the mass and axial stiffness of the fluid column, the oscillatory pulse of the piston, and the hydraulic impedance of the rocket engine. The model was used to determine the relations between piston stroke, pressure oscillation at the engine inlet, and structural excitation of the feedline. This paper develops the concepts employed by the model.

Saxon, J. B.↗

NASA NTRS1984

Numerical Investigation of unsteady inlet flow fields

The flow field within an unsteady, two-dimensional inlet is studied numerically, using a two dimensional Navier Stokes and a one-dimensional inviscid model. Unsteadiness is introduced by varying the outflow pressure boundary condition. The cases considered include outflow pressure variations which were a single pressure pulse, a rapid increase and a sine function. The amplitude of the imposed exit plane pressure disturbance varied between 1 percent and 20 percent of the mean exit pressure. At the higher levels of pressure fluctuation, the viscous flow field results bore little resemblance to the inviscid ones. The viscous solution included such phenomena as shock trains and bifurcating separation pockets. The induced velocity at the outflow plane predicted by the viscous model differs significantly from accoustical theory or small perturbation results.

Hsieh, T.↗

NASA NTRS1997

Dynamic Nucleation of Ice Induced by a Single Stable Cavitation Bubble

Dynamic nucleation of ice induced by caviation bubble in undercooled water is observed using an acoustic levitation technique. The observation indicates that a high pressure pulse associated with a collapsing bubble is indeed responsible for the nucleation of a high pressure phase of ice.

Nucleation of Ice Caviation Bubble↗

NASA NTRS1967

High-energy-rate magnetohydraulic metal forming system

In the magnetohydraulic metal forming system, a sonic shock wave is generated in a liquid medium by a coil energized by an electrical discharge. These waves transfer energy from a metal diaphragm, actuated by a pulsed magnetic field, to a metal workpiece. In the development a study was made of the pressure pulse phenomenon in a liquid medium.

Source record↗

NASA NTRS1990

The AMPTE lithium releases in the solar wind - A possible trigger for geomagnetic pulsations

Shortly after the AMPTE/IRM satellite had released Lithium ions into the solar wind, magnetometers on the ground and in the frontside magnetosphere observed deflections of a type similar to those associated with solar wind pressure pulses. Since the natural solar wind was very stable during this event and did not exhibit pressure changes, the magnetic deflections have likely been caused by the artificially injected Lithium cloud when it hit the magnetosphere. Order of magnitude estimates show that 300 g of Lithium vapor released in the solar wind are indeed able to produce a 300 nT magnetic deflection on the ground under favorable conditions.

Luehr, Hermann↗

NASA NTRS1973

Flow characteristics in the exhaust of a pulsed megawatt gas fed arc

The transient flow generated by a pulsed, megawatt-level, gas-fed arc with an applied magnetic nozzle has been examined with a new design piezoelectric pressure transducer. Sensor thermal conduction and accelerations have been examined and eliminated in the 500 microsec period of plasma flow. Existence of a large magnitude cold gas pressure front of 20 microsec duration has been reconfirmed and its relationship to the following plasma flow of about 200 microsec duration has been examined for the first time. At a point 30 cm from the arc source, initially near vacuum conditions (typically with an arc current of 11.2 kA and 1 tesla applied magnetic field), a pressure pulse of unionized gas with a magnitude of 10,000 N/sq m is followed by plasma flows with nearly constant impact pressure of 1000 N/sq m. Pressure and number density in this plasma region are seen to decrease with applied magnetic field strength.

Michels, C. J.↗

NASA NTRS1976

Fluid-plasticity of thin cylindrical shells

Dynamic plastic response of a thin cylindrical shell, immersed in a potential fluid initially at rest and subjected to internal pressure pulse of arbitrary shape and duration, is examined. The shell is assumed to respond as a rigid-perfectly plastic material while the fluid is taken as inviscid and incompressible. The fluid back pressure is incorporated into the equation of motion of the shell as an added mass term. Since arbitrary pulses can be reduced to equivalent rectangular pulses, the equation of motion is solved only for a rectangular pulse. The influence of the fluid in reducing the final plastic deformation is demonstrated by a numerical example.

Krajcinovic, D.↗

NASA NTRS1988

Correlation of macro and micro cardiovascular function during weightlessness and simulated weightlessness

The investigation of cardiovascular function necessarily involves a consideration of the exchange of substances at the capillary. If cardiovascular function is compromised or in any way altered during exposure to zero gravity in space, then it stands to reason that microvascular function is also modified. We have shown that an increase in cardiac output similar to that reported during simulated weightlessness is associated with a doubling of the number of post-capillary venules and a reduction in the number of arterioles by 35%. If the weightlessness of space travel produces similar changes in cardiopulmonary volume and cardiac output, a reasonable expectation is that astronauts will undergo venous neovascularization. We have developed an animal model in which to correlate microvascular and systemic cardiovascular function. The microcirculatory preparation consists of a lightweight, thermo-neutral chamber implanted around intact skeletal muscle on the back of a rat. Using this technique, the performed microvasculature of the cutaneous maximus muscle may be observed in the conscious, unanesthetized animal. Microcirculatory variables which may be obtained include venular and arteriolar numbers, lengths and diameters, single vessel flow velocities, vasomotion, capillary hematocrit anastomoses and orders of branching. Systemic hemodynamic monitoring of cardiac output by electromagnetic flowmetry, and arterial and venous pressures allows correlation of macro- and microcirculatory changes at the same time, in the same animal. Observed and calculated hemodynamic variables also include pulse pressure, heart rate, stroke volume, total peripheral resistance, aortic compliance, minute work, peak aortic flow velocity and systolic time interval. In this manner, an integrated assessment of total cardiovascular function may be obtained in the same animal without the complicating influence of anesthetics.

NASA Discipline Number 00-00↗

NASA NTRS1971

Inertia diaphragm pressure transducer

Transducer measures gas pressure profiles in high temperature, short duration, gas flows usually found in devices where pressure pulses may have durations of few microseconds to several milliseconds. Assembly includes fluid delay line, delay chamber, and flow restrictor for equalizing steady state pressure on diaphragm's sides

Seegmiller, H. L. B.↗

NASA NTRS1972

Design of a specialized computer for on-line monitoring of cardiac stroke volume

The design of a specialized analog computer for on-line determination of cardiac stroke volume by means of a modified version of the pressure pulse contour method is presented. The design consists of an analog circuit for computation and a timing circuit for detecting necessary events on the pressure waveform. Readouts of arterial pressures, systolic duration, heart rate, percent change in stroke volume, and percent change in cardiac output are provided for monitoring cardiac patients. Laboratory results showed that computational accuracy was within 3 percent, while animal experiments verified the operational capability of the computer. Patient safety considerations are also discussed.

Webb, J. A., Jr.↗

NASA NTRS1982

Pressure pulsations above turbomolecular pumps

Lange and Singleton (1978) have observed pressure pulses above a turbomolecular pump. They reported that the mean pulse frequency increased with the temperature of the pump cooling water and that the evolved gas was mainly hydrogen. The present investigation takes into account tests conducted with a similar pumping system. The pumping system was equipped with additional pressure-monitoring equipment in order to study these pulsations in more detail. It was found that at least two distinct types of pressure pulsations may be present in a turbomolecular-pumped ultrahigh vacuum system. The random hydrogen pulses are easily eliminated for period of days by changing the cooling water temperature. The cyclic pulses consisting mainly of water vapor are not likely to be a problem in normal experiments.

Danziger, S.↗

NASA NTRS1977

Influence of low and high pressure baroreceptors on plasma renin activity in humans

The effects of low and high pressure baroreceptors on plasma renin activity (immunoassay) were evaluated using graded lower body suction (LBS) in six healthy men. LBS at -10 and -20 mmHg for 10 min decreased central venous pressure without changing arterial pressure and thereby presumably reduced low but not high pressure baroreceptor inhibition of renin release. LBS at these levels produced forearm vasoconstriction, but did not increase renin. LBS at -40 mmHG decreased central venous and arterial pulse pressure and thus reduced both low and high pressure baroreceptor inhibition. LBS at this level produced forearm vasoconstriction and tachycardia and increased renin. In summary, reduction in low pressure baroreceptor inhibition in humans did not increase renin in the presence of physiological tonic inhibition from high pressure baroreceptors. Increases in renin did not occur until there was combined reduction of high and low pressure baroreceptor inhibition on plasma renin activity.

Mark, A. L.↗

NASA NTRS2011

Water Flow Testing and Unsteady Pressure Analysis of a Two-Bladed Liquid Oxidizer Pump Inducer

The unsteady fluid dynamic performance of a cavitating two-bladed oxidizer turbopump inducer was characterized through sub-scale water flow testing. While testing a novel inlet duct design that included a cavitation suppression groove, unusual high-frequency pressure oscillations were observed. With potential implications for inducer blade loads, these high-frequency components were analyzed extensively in order to understand their origins and impacts to blade loading. Water flow testing provides a technique to determine pump performance without the costs and hazards associated with handling cryogenic propellants. Water has a similar density and Reynolds number to liquid oxygen. In a 70%-scale water flow test, the inducer-only pump performance was evaluated. Over a range of flow rates, the pump inlet pressure was gradually reduced, causing the flow to cavitate near the pump inducer. A nominal, smooth inducer inlet was tested, followed by an inlet duct with a circumferential groove designed to suppress cavitation. A subsequent 52%-scale water flow test in another facility evaluated the combined inducer-impeller pump performance. With the nominal inlet design, the inducer showed traditional cavitation and surge characteristics. Significant bearing loads were created by large side loads on the inducer during synchronous cavitation. The grooved inlet successfully mitigated these loads by greatly reducing synchronous cavitation, however high-frequency pressure oscillations were observed over a range of frequencies. Analytical signal processing techniques showed these oscillations to be created by a rotating, multi-celled train of pressure pulses, and subsequent CFD analysis suggested that such pulses could be created by the interaction of rotating inducer blades with fluid trapped in a cavitation suppression groove. Despite their relatively low amplitude, these high-frequency pressure oscillations posed a design concern due to their sensitivity to flow conditions and test scale. The amplitude and frequency of oscillations varied considerably over the pump s operating space, making it difficult to predict blade loads.

Schwarz, Jordan B.↗

NASA NTRS1993

Hover Acoustic Characteristics of the XV-15 with Advanced Technology Blades

An experiment has been performed to investigate the far-field hover acoustic characteristics of the XV-15 aircraft with advanced technology blades (ATB). An extensive, high-quality, far-field acoustics data base was obtained for a rotor tip speed range of 645-771 ft/s. A 12-microphone, 500-ft radius semicircular array combined with two aircraft headings provided acoustic data over the full 360-deg azimuth about the aircraft with a resolution of 15 deg. Altitude variations provided data from near in-plane to 45 deg below the rotor tip path plane. Acoustic directivity characteristics in the lower hemisphere are explored through pressure time histories, narrow-band spectra, and contour plots. Directivity patterns were found to vary greatly with azimuth angle, especially in the forward quadrants. Sharp positive pressure pulses typical of blade-vortex interactions were found to propagate aft of the aircraft and were most intense at 45 deg below the rotor plane. Modest overall sound pressure levels were measured near in-plane indicating that thickness noise is not a major problem for this aircraft when operating in the hover mode with ATB. Rotor tip speed reductions reduced the average overall sound pressure level (dB (0.0002 dyne/cm(exp 2)) by nearly 8 dB in-plane, and 12.6 deg below the rotor plane.

Conner, David A.↗

NASA NTRS2002

Autonomic neural control of dynamic cerebral autoregulation in humans

BACKGROUND: The purpose of the present study was to determine the role of autonomic neural control of dynamic cerebral autoregulation in humans. METHODS AND RESULTS: We measured arterial pressure and cerebral blood flow (CBF) velocity in 12 healthy subjects (aged 29+/-6 years) before and after ganglion blockade with trimethaphan. CBF velocity was measured in the middle cerebral artery using transcranial Doppler. The magnitude of spontaneous changes in mean blood pressure and CBF velocity were quantified by spectral analysis. The transfer function gain, phase, and coherence between these variables were estimated to quantify dynamic cerebral autoregulation. After ganglion blockade, systolic and pulse pressure decreased significantly by 13% and 26%, respectively. CBF velocity decreased by 6% (P<0.05). In the very low frequency range (0.02 to 0.07 Hz), mean blood pressure variability decreased significantly (by 82%), while CBF velocity variability persisted. Thus, transfer function gain increased by 81%. In addition, the phase lead of CBF velocity to arterial pressure diminished. These changes in transfer function gain and phase persisted despite restoration of arterial pressure by infusion of phenylephrine and normalization of mean blood pressure variability by oscillatory lower body negative pressure. CONCLUSIONS: These data suggest that dynamic cerebral autoregulation is altered by ganglion blockade. We speculate that autonomic neural control of the cerebral circulation is tonically active and likely plays a significant role in the regulation of beat-to-beat CBF in humans.

Non-NASA Center↗

NASA NTRS1965

Blood-Pressure Measuring System Gives Accurate Graphic Output

The problem: To develop an instrument that will provide an external (indirect) measurement of arterial blood pressure in the form of an easily interpreted graphic trace that can be correlated with standard clinical blood-pressure measurements. From sphygmograms produced by conventional sphygmographs, it is very difficult to differentiate the systolic and diastolic blood-pressure pulses and to correlate these indices with the standard clinical values. It is nearly impossible to determine these indices when the subject is under physical or emotional stress. The solution: An electronic blood-pressure system, basically similar to conventional ausculatory sphygmomanometers, employing a standard occluding cuff, a gas-pressure source, and a gas-pressure regulator and valve. An electrical output transducer senses cuff pressure, and a microphone positioned on the brachial artery under the occluding cuff monitors the Korotkoff sounds from this artery. The output signals present the conventional systolic and diastolic indices in a clear, graphical display. The complete system also includes an electronic timer and cycle-control circuit.

Source record↗

NASA NTRS1987

Numerical modeling of the vortex/airfoil interaction

A modeling of the vortex-airfoil interaction is presented in which the finite-area of the real vortices is taken into consideration. Two vortex models are used. In the first, a disturbed piece of vorticity layer is simulated by four rows of discrete vortices of small strength. In the second, a number of discrete vortices is arranged within a circle. The first model may simulate a shear layer or a wake, while the second, a well-formed vortex. The method was applied to the calculation of the pressure induced on the surface of the airfoil by the interacting vortex. Both models give similar results. It was found that for large distances of the vortex from the surface of the airfoil, the consideration or not of the finite-area of the vortex is not a significant factor in determining the induced pressure field. However, when the distance of the vortex from the surface is reduced, its shape is distorted and the induced pressure pulses have lower amplitude than the ones induced by an equivalent point vortex. In the limit, where the vortex impinges on the leading edge of the airfoil, it is split into two and the time dependent pressure coefficient takes even negative values at some time intervals.

Panaras, Argyris G.↗

NASA NTRSDate not supplied

Development of an Ejectable Data Recorder Ejection Mechanism for the Low Earth Orbit Flight Test of an Inflatable Decelerator

On November 10, 2022, the 1100kg (2,425 lbs.) LOFTID Reentry Vehicle (RV) was launched on a United Launch Alliance Atlas V as a secondary payload with the Joint Polar Surveyor System-2. The 6-meter diameter (~20 ft.) aeroshell (a type of heat shield) entered the atmosphere at 8 kilometers per second (18,000 miles per hour), and flew nominally, enduring the intended heat pulse that saw temperatures exceeding 1371˚C (2500˚F) on the front side while the payload skin remained only about 38˚C (100˚F). The RV exceeded Mach 30 and the heat-affected aeroshell withstood a pressure pulse that exerted 9g’s deceleration maintaining stable flight through the hypersonic, supersonic, transonic, and subsonic regimes to the parachute deployment. As part of the Agency’s strategic goal “to extend human presence deeper into space and to the moon for sustainable long-term exploration and utilization”, the LOFTID inflatable aerodynamic decelerator or aeroshell technology could one day help land humans on Mars. As with any flight test, data collection is of utmost importance. Without a data downlink and a possibility of the RV sinking before the recovery crew got to it, a secondary data collection method was introduced. The RV would eject a data recorder, which would have a duplicate copy of the on-board flight date, before splashdown and be retrieved separately. This paper discusses the development of the ejection mechanism used to eject the data recorder from the RV during the test flight. The development includes discussions of design constraints, a design overview, the testing program, and lessons learned throughout the process all the way through successful data recorder recovery.

mechanism↗