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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

The Effect of Acoustic Disturbances on the Operation of the Space Shuttle Main Engine Fuel Flowmeter

The Space Shuttle Main Engine (SSME) uses a turbine fuel flowmeter (FFM) in its Low Pressure Fuel Duct (LPFD) to measure liquid hydrogen flowrates during engine operation. The flowmeter is required to provide accurate and robust measurements of flow rates ranging from 10000 to 18000 GPM in an environment contaminated by duct vibration and duct internal acoustic disturbances. Errors exceeding 0.5% can have a significant impact on engine operation and mission completion. The accuracy of each sensor is monitored during hot-fire engine tests on the ground. Flow meters which do not meet requirements are not flown. Among other parameters, the device is screened for a specific behavior in which a small shift in the flow rate reading is registered during a period in which the actual fuel flow as measured by a facility meter does not change. Such behavior has been observed over the years for specific builds of the FFM and must be avoided or limited in magnitude in flight. Various analyses of the recorded data have been made prior to this report in an effort to understand the cause of the phenomenon; however, no conclusive cause for the shift in the instrument behavior has been found. The present report proposes an explanation of the phenomenon based on interactions between acoustic pressure disturbances in the duct and the wakes produced by the FFM flow straightener. Physical insight into the effects of acoustic plane wave disturbances was obtained using a simple analytical model. Based on that model, a series of three-dimensional unsteady viscous flow computational fluid dynamics (CFD) simulations were performed using the MSFC PHANTOM turbomachinery code. The code was customized to allow the FFM rotor speed to change at every time step according to the instantaneous fluid forces on the rotor, that, in turn, are affected by acoustic plane pressure waves propagating through the device. The results of the simulations show the variation in the rotation rate of the flowmeter due to the interaction of the flow straightener wakes and the upstream propagating acoustic waves. A detailed analysis of the acoustic disturbance effects is presented along with an assessment of the impact on measurement accuracy.

Marcu, Bogdan↗
NASA NTRS1972

Investigation of the stability of the tip vortex generated by hovering propellers and rotors.

The objective of this experimental and theoretical investigation was to determine what factors and mechanisms are involved in vortex interaction and instability and how these phenomena manifest themselves. To answer these questions, the schlieren method of flow visualization was used to observe the wakes generated by two- and four-bladed model propellers and rotors. A concurrent free-wake analysis was conducted for comparative purposes. Schlieren pictures showing wake asymmetry, interaction, and instability are presented. Various factors and mechanisms believed to be responsible for these are discussed along with the effects produced by the number of blades, collective pitch, and tip speed. Free-wake calculations that qualitatively confirm those factors responsible for wake asymmetry and interaction are also presented.

Tangler, J. L.↗
NASA NTRS2008

SmaggIce 2.0: Additional Capabilities for Interactive Grid Generation of Iced Airfoils

The Surface Modeling and Grid Generation for Iced Airfoils (SmaggIce) software toolkit has been extended to allow interactive grid generation for multi-element iced airfoils. The essential phases of an icing effects study include geometry preparation, block creation and grid generation. SmaggIce Version 2.0 now includes these main capabilities for both single and multi-element airfoils, plus an improved flow solver interface and a variety of additional tools to enhance the efficiency and accuracy of icing effects studies. An overview of these features is given, especially the new multi-element blocking strategy using the multiple wakes method. Examples are given which illustrate the capabilities of SmaggIce for conducting an icing effects study for both single and multi-element airfoils.

Kreeger, Richard E.↗
NASA NTRS2009

Stability Analysis of Roughness Array Wake in a High-Speed Boundary Layer

Computations are performed to examine the effects of both an isolated and spanwise periodic array of trip elements on a high-speed laminar boundary layer, so as to identify the potential physical mechanisms underlying an earlier transition to turbulence as a result of the trip(s). In the context of a 0.333 scale model of the Hyper-X forebody configuration, the time accurate solution for an array of ramp shaped trips asymptotes to a stationary field at large times, indicating the likely absence of a strong absolute instability in the mildly separated flow due to the trips. A prominent feature of the wake flow behind the trip array corresponds to streamwise streaks that are further amplified in passing through the compression corner. Stability analysis of the streaks using a spatial, 2D eigenvalue approach reveals the potential for a strong convective instability that might explain the earlier onset of turbulence within the array wake. The dominant modes of streak instability are primarily sustained by the spanwise gradients associated with the streaks and lead to integrated logarithmic amplification factors (N factors) approaching 7 over the first ramp of the scaled Hyper-X forebody, and substantially higher over the second ramp. Additional computations are presented to shed further light on the effects of both trip geometry and the presence of a compression corner on the evolution of the streaks.

Choudhari, Meelan↗
NASA NTRS1977

A computationally fast one-dimensional diffusion-photochemistry model of SST wakes

A computational technique applicable to analysis of supersonic transport (SST) wake photochemistry and diffusion is presented. Sensitivity studies of SST effluent effects upon ozone depletion are facilitated by the computational rapidity of the method. The article compares results from other studies and predictions of some variables related to global NOx input. Results indicate that the NO/NO2 ratio in an SST wake at photochemical equilibrium is a sensitive function of photolysis rates.

Matloff, G. L.↗
NASA NTRS1980

Three dimensional mean flow and turbulence characteristics of the near wake of a compressor rotor blade

The investigation was carried out using the rotating hot wire technique. Measurements were taken inside the end wall boundary layer to discern the effect of annulus and hub wall boundary layer, secondary flow, and tip leakage on the wake structure. Static pressure gradients across the wake were measured using a static stagnation pressure probe insensitive to flow direction changes. The axial and the tangential velocity defects, the radial component of velocity, and turbulence intensities were found to be very large as compared to the near and far wake regions. The radial velocities in the trailing edge region exhibited characteristics prevalent in a trailing vortex system. Flow near the blade tips found to be highly complex due to interaction of the end wall boundary layers, secondary flows, and tip leakage flow with the wake. The streamwise curvature was found to be appreciable near the blade trailing edge. Flow properties in the trailing edge region are quite different compared to that in the near and far wake regions with respect to their decay characteristics, similarity, etc. Fourier decomposition of the rotor wake revealed that for a normalized wake only the first three coefficients are dominant.

Ravindranath, A.↗
NASA NTRS1977

Aerodynamic interference effects on tilting proprotor aircraft

The Green's function method was used to study tilting proprotor aircraft aerodynamics with particular application to the problem of the mutual interference of the wing-fuselage-tail-rotor wake configuration. While the formulation is valid for fully unsteady rotor aerodynamics, attention was directed to steady state aerodynamics, which was achieved by replacing the rotor with the actuator disk approximation. The use of an actuator disk analysis introduced a mathematical singularity into the formulation; this problem was studied and resolved. The pressure distribution, lift, and pitching moment were obtained for an XV-15 wing-fuselage-tail rotor configuration at various flight conditions. For the flight configurations explored, the effects of the rotor wake interference on the XV-15 tilt rotor aircraft yielded a reduction in the total lift and an increase in the nose-down pitching moment. This method provides an analytical capability that is simple to apply and can be used to investigate fuselage-tail rotor wake interference as well as to explore other rotor design problem areas.

Soohoo, P.↗
NASA NTRS1991

Prediction of unsteady rotor-surface pressure and heat transfer from wake passings

The research described in this paper is a numerical investigation of the effects of unsteady flow on gas turbine heat transfer, particularly on a rotor blade surface. The unsteady flow in a rotor blade passage and the unsteady heat transfer on the blade surface as a result of wake/blade interaction are modeled by the inviscid flow/boundary layer approach. The Euler equations which govern the inviscid flow are solved using a time-accurate marching scheme. The unsteady flow in the blade passage is induced by periodically moving a wake model across the passage inlet. Unsteady flow solutions in the passage provide pressure gradients and boundary conditions for the boundary-layer equations which govern the viscous flow adjacent to the blade surface. Numerical solutions of the unsteady turbulent boundary layer yield surface heat flow values which can then be compared to experimental data. Comparisons with experimental data show that unsteady heat flux on the blade suction surface is well predicted, but the predictions of unsteady heat flux on the blade pressure surface do not agree.

Tran, Le T.↗
NASA NTRSDate not supplied

Single-Component Average Velocity Profiles in the Wake of the Orion Crew Capsule at the National Transonic Facility

A minimally intrusive molecular tagging instrument measured single-component average velocity profiles in two planes in the wake of the Orion capsule with different heat shield configurations in the National Transonic Facility at the NASA Langley Research Center. Reynolds number effects at subsonic conditions have proven difficult to predict due to the largely separated wake flow. Therefore two measurement planes in the wake of the model were probed to measure the wake profile for different heat shield configurations and act as a validation reference for computational tools. Air testing included Mach numbers of 0.3, 0.5, and 0.7 at Reynolds numbers of 5.3 and 7.5 million. In cryogenic nitrogen, the instrument was employed under transient conditions during the facility warm up at M = 0.3 with decreasing Reynolds numbers from 16 million. An exhaustive list of the results is shown and discussed here. For free transition heat shield configurations, the size of the wake was found to increase with Mach number, yet remain constant with Reynolds number for low (M = 0.3) and high (M = 0.7) subsonic Mach numbers. However, intermediate Mach numbers (M = 0.5) showed that the wake was smaller at higher Reynolds numbers for the IDAT heat shield. The addition of surface roughness in the form of grit, known as the fixed transition cases, negated any Mach number dependence to the wake profile and increased the size of the wake for all cases.

Velocimetry↗
NASA NTRSDate not supplied

Single-Component Average Velocity Profiles in the Wake of the Orion Crew Capsule at the National Transonic Facility

A minimally intrusive molecular tagging instrument measured single-component average velocity profiles in two planes in the wake of the Orion capsule with different heat shield configurations in the National Transonic Facility at the NASA Langley Research Center. Reynolds number effects at subsonic conditions have proven difficult to predict due to the largely separated wake flow. Therefore two measurement planes in the wake of the model were probed to measure the wake profile for different heat shield configurations and act as a validation reference for computational tools. Air testing included Mach numbers of 0.3, 0.5, and 0.7 at Reynolds numbers of 5.3 and 7.5 million. In cryogenic nitrogen, the instrument was employed under transient conditions during the facility warm up at M = 0.3 with decreasing Reynolds numbers from 16 million. An exhaustive list of the results is shown and discussed here. For free transition heat shield configurations, the size of the wake was found to increase with Mach number, yet remain constant with Reynolds number for low (M = 0.3) and high (M = 0.7) subsonic Mach numbers. However, intermediate Mach numbers (M = 0.5) showed that the wake was smaller at higher Reynolds numbers for the IDAT heat shield. The addition of surface roughness in the form of grit, known as the fixed transition cases, negated any Mach number dependence to the wake profile and increased the size of the wake for all cases.

Velocimetry↗
NASA NTRS1986

Unsteady heat transfer and direct comparison to steady-state measurements in a rotor-wake experiment

Circumferentially local and time-resolved heat transfer measurements were obtained for a circular cylinder in crossflow located downstream of a rotating spoked wheel wake generator in a steady flow tunnel. The unsteady heat transfer effects were obtained by developing an extension of a thin film gauge technique employed to date exclusively in short-duration facilities. The time-average thin film results and conventional steady-state heat transfer measurements were compared. Time-averaged wake-induced stagnation heat transfer enhancement levels above the nowake case were about 10% for the four cylinder Reynolds numbers. This enhancement level was nearly independent of bar passing frequency and was related directly to the time integral of the heat transfer spikes observed at the bar passing frequency. It is observed that the wake-induced heat transfer spikes have peak magnitudes averaging 30 to 40% above the interwake heat transfer level.

Obrien, J. E.↗
NASA NTRS1986

Unsteady heat transfer and direct comparison to steady-state measurements in a rotor-wake experiment

Circumferentially local and time-resolved heat transfer measurements were obtained for a circular cylinder in crossflow located downstream of a rotating spoked wheel wake generator in a steady flow tunnel. The unsteady heat transfer effects were obtained by developing an extension of a thin film gauge technique employed to date exclusively in short-duration facilities. The time-average thin film results and conventional steady-state heat transfer measurements were compared. Time-averaged wake-induced stagnation heat transfer enhancement levels above the nowake case were about 10 percent for the four cylinder Reynolds numbers. This enhancement level was nearly independent of bar passing frequency and was related directly to the time integral of the heat transfer spikes observed at the bar passing frequency. It is observed that the wake-induced heat transfer spikes have peak magnitudes averaging 30 to 40 percent above the interwake heat transfer level.

Obrien, J. E.↗
NASA NTRS1988

Positioning Rotors In Turbine Flowmeters

Lengths of wakes roughly proportional to thickness of vanes. Mathematical model simplifies analysis of effects of flow-straightening vanes in turbine flowmeter. Yields numerical solution of differential equations of flow for quick examination of efforts of thicknesses of vanes and rate of flow on extent of wake behind vanes. From examination, minimum distance at which flowmeter rotor placed behind vanes determined.

Lynch, Edward D.↗
NASA NTRS1985

The effect of hydrodynamic turbulence on Langmuir waves in a slightly ionized plasma

In the lower altitude regions of the ionosphere, the gas present is only slightly ionized, and it behaves as a fluid. It is expected that a turbulent wake will form behind a spacecraft. Information is to be obtained regarding the effect of this turbulence on plasma waves measured by the spacecraft. If the turbulence is two-dimensional (2-D) and carries enstrophy, a fluctuating magnetic field and electric fields are produced. The fields induce fluctuations in the electron population which correlate with the magnetic and electric fluctuations which produced them. This correlation causes diffusion which changes the electron distribution and heats the electrons. As a result, the Langmuir frequency increases, and the Landau damping of Langmuir waves in the plasma decreases. Details regarding these processes are discussed, taking into account the results of a mathematical analysis.

Parish, J. L.↗
NASA NTRS1974

Further analysis of broadband noise measurements for a rotating blade operating with and without its shed wake blown downstream

An experimental investigation has been conducted to investigate the broadband noise generated by a rotating-blade system. Tests were made with circular and NACA 0012 rotor-blade sections. The blades were operated only with zero lift at each radial station. Tests were made both with zero axial velocity, so that the blades operated in their own turbulent wake, and with a small axial velocity imposed by the wind tunnel to blow the wake of one blade away before the passage of the next blade. The rotor with cylindrical blades generally radiated more noise throughout the noise spectrum than did the rotor with airfoil blades. Blowing the blade wake away from the rotor with cylindrical blades did not have any appreciable effect on the amplitude frequency spectrum, and the predominant noise was broadband, either with tunnel wind on or off. For the rotor with airfoil blades, however, blowing the blade wake away changed the character of the noise spectrum completely in that broadband noise was eliminated or diminished to such an extent as to be indistinguishable. The broadband noise of the airfoil-bladed rotor with zero axial velocity is apparently caused by lift fluctuations due to velocity components of the turbulence normal to the plane of rotation.

Scheiman, J.↗
NASA NTRS1971

Some implications of satellite spin effects in cylindrical probe measurements

In-situ measurements of ambient electron densities with satellite-borne cylindrical probes exhibit periodic variations synchronous with the satellite's spin cycle. Representing these fluctuations as a superposition of effects attributable to both the presence of the satellite wake and the geomagnetic field leads to a model of the modulations of accelerated electron current to cylindrical probes in which one modulation component displays current variations dependent upon the probe-velocity angle (psi) and the other displays variations dependent upon the angle between the probe axis and the geomagnetic field lines (beta). The modulations produce an electron current decrease whenever the probe axis rotates into the satellite wake or whenever the probe axis rotates toward alignment with the geomagnetic field lines. With increasing altitude, the modulation dependent upon psi decreases whereas the modulation dependent upon beta increases. The analysis results imply that the most accurate of atmospheric electron densities by satellite-borne cylindrical probes come from measurements taken out of the satellite's wake and when the probe axis is within 20 degrees of being perpendicular to the geomagnetic field lines.

Miller, N. J.↗
NASA NTRS1972

Some implications of satellite spin effects in cylindrical probe measurements.

Observation that in situ measurements of ambient electron densities with satellite-borne cylindrical probes exhibit periodic variations synchronous with the satellite spin cycle. Representing these fluctuations as a superposition of effects attributable to both the presence of the satellite wake and the geomagnetic field leads to a model of the modulations of accelerated electron current to cylindrical probes in which one modulation component displays current variations dependent on the probe velocity angle (psi), and the other displays variations dependent on the angle between the probe axis and the geomagnetic-field lines (beta). The modulations produce an electron current decrease whenever the probe axis rotates into the satellite wake or whenever the probe axis rotates toward alignment with the geomagnetic-field lines. As altitude increases, the modulation dependent on psi decreases, whereas the modulation dependent on beta increases. The psi-dependent modulation component can be associated with the presence of a wake structure, and the beta-dependent component can be associated with the magnetic influence on the transport properties of thermal electrons, assuming that the electron fluxes are predominant along the field lines. The analysis results imply that the most accurate determinations of atmospheric electron densities by satellite-borne cylindrical probes come from measurements taken out of the wake of the satellite when the probe axis is within 20 deg of being perpendicular to the geomagnetic-field lines.

Miller, N. J.↗