Nonlinear combustion instability in liquid- propellant rocket engines
Nonlinear combustion instability in liquid propellant rocket engines, describing unsteady combustor flow with single wave equation
Powell, E. A.↗
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Results for “flow instability”
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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Experimental investigation of recirculating cells in laminar coaxial jets.
Utilizing several unique means of introducing smoke into the flow field for careful visualization in addition to hot-wire techniques, experiments are performed in a specially designed facility producing laminar flows up to considerably high Reynolds numbers. Characteristics of the cells and the flow conditions that bring them about are documented by smoke photographs in the Reynolds number velocity ratio plane and the results are compared to previous analytical predictions. The cells are found to fall into three categories with different flow characteristics involving unsteadiness in position, and shear layer instabilities which result in higher mixing with the outer streams.-
Warpinski, N. R.↗
Magnetic field merging in the solar wind
Magnetic field merging in the solar wind is discussed in terms of steady-state merging, which involves a steady flow field, and of spontaneous merging, which involves an instability such as the tearing instability. Spontaneous merging is found to be more effective than steady-state merging.
Schindler, K.↗
Effect of a bulge on the secondary instability of boundary layers
The influence of a two-dimensional hump on the three-dimensional (3-D) subharmonic secondary instability on a flat plate is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for the inviscid/viscous interaction. The primary wave is taken in the form of a two-dimensional (2-D) Tollmien-Schlichting (T-S) wave. The secondary wave is taken in the form of a 3-D subharmonic T-S wave.
Nayfeh, Ali H.↗
Stability of three-dimensional boundary layers
The computational modeling of the transition process characteristic of flows over swept wings is discussed. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full three-dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that regular stability theory is insufficient to explain the discrepancies between experiments and between theory and experiment. The leading edge region of a swept wing will be considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.
Reed, Helen L.↗
Effect of a bulge on the subharmonic instability of boundary layers
The influence of a two-dimensional hump on the three-dimensional (3-D) subharmonic secondary instability on a flat plate is investigated. The mean flow is calculated by using interacting boundary layers, thereby accounting for the viscid/inviscid interaction. The primary wave is taken in the form of a two-dimensional (2-D) Tollmien-Schlichting (T-S) wave. The secondary wave is taken in the form of a 3-D subharmonic wave. The results show that increasing the hump height results in an increase in the amplification factors of the primary and subharmonic waves. When the hump causes separation, the growth rates of both the primary and subharmonic waves are considerably larger than those obtained in the case of no separation.
Nayfeh, Ali H.↗
Numerical simulation of swept-wing flows
The transition process characteristics of flows over swept wings were computationally modelled. The crossflow instability and crossflow/T-S wave interaction are analyzed through the numerical solution of the full three dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. The leading-edge region of a swept wing is considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.
Reed, Helen L.↗
Numerical simulation of swept-wing flows
Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.
Reed, Helen L.↗
Effects of Gravity on the Transition to Turbulence of Gas Jet Diffusion Flames
An ongoing study of the transition to turbulence of gas jet diffusion flames conducted in a reduced microgravity environment at the NASA Lewis 2.2 second drop tower is described. The experiments were based on propane injected into quiescent air. Several differences with the corresponding normal gravity process were observed. In particular, large scale structures appeared intermittently in microgravity which are manifested at the flame base and convected down stream. As the Reynolds number increased, a continuous train of structures was observed along the flame front. These observations are explained by instability of the shear layer associated with injection of flow into quiescent surroundings.
Bahadori, M. Y.↗
Coordinated Studies of Magnetospheric/Ionospheric Coupling and Dynamics in the Diffuse Aurora
The results of the studies carried out under the grant are described in detail in the following publications: Atmospheric Response in Aurora experiment: Observations of E and F region neutral winds in a region of postmidnight diffuse aurora; Walterscheid, Modified geostrophy in the thermosphere, ARIA II neutral flywheel-driven field-aligned currents in the postmidnight sector of the auroral oval: A case study; Observations of unstable atmospheric shear layers in the lower E region in the post-midnight auroral oval; and Depletion of oxygen in aurora: Evidence for a local mechanism. The objective of the Atmospheric Response in Aurora (ARIA) experiment was to measure the response of the E-region neutral flow to substorm activity in the post-midnight sector of the auroral oval. To this end, neutral wind profiles were obtained from a series of four sets of rocket flights using the chemical release technique. The measurements covered conditions ranging from quiet to disturbed. A consistent feature of the observed winds in disturbed conditions is the presence of an E-region jet located between approximately 110 and 120 km altitude. The profiles presented here show that the neutral wind speeds near 110-120 km altitude increase and the hodographs become more elongated or linear in response to higher magnetic activity levels. The wind speeds decrease and the hodographs become more circular as the activity level decreases. The presence of a wind maximum implies shears both above and below. The observations consistently show larger shears below the peak and smaller shears above. In fact, the bottom-side shears during disturbed conditions have Richardson numbers close to or below the critical value of 0.25 suggesting that the flow is highly unstable in that height range. The instability is expected to produce waves, turbulence, and enhanced diffusivity.
Larsen, M. F.↗
Fluid Physical and Transport Phenomena Studies aboard the International Space Station: Planned Experiments
This paper provides an overview of the microgravity fluid physics and transport phenomena experiments planned for the International Spare Station. NASA's Office of Life and Microgravity Science and Applications has established a world-class research program in fluid physics and transport phenomena. This program combines the vast expertise of the world research community with NASA's unique microgravity facilities with the objectives of gaining new insight into fluid phenomena by removing the confounding effect of gravity. Due to its criticality to many terrestrial and space-based processes and phenomena, fluid physics and transport phenomena play a central role in the NASA's Microgravity Program. Through widely publicized research announcement and well established peer-reviews, the program has been able to attract a number of world-class researchers and acquired a critical mass of investigations that is now adding rapidly to this field. Currently there arc a total of 106 ground-based and 20 candidate flight principal investigators conducting research in four major thrust areas in the program: complex flows, multiphase flow and phase change, interfacial phenomena, and dynamics and instabilities. The International Space Station (ISS) to be launched in 1998, provides the microgravity research community with a unprecedented opportunity to conduct long-duration microgravity experiments which can be controlled and operated from the Principal Investigators' own laboratory. Frequent planned shuttle flights to the Station will provide opportunities to conduct many more experiments than were previously possible. NASA Lewis Research Center is in the process of designing a Fluids and Combustion Facility (FCF) to be located in the Laboratory Module of the ISS that will not only accommodate multiple users but, allow a broad range of fluid physics and transport phenomena experiments to be conducted in a cost effective manner.
Singh, Bhim S.↗
MESSENGER Orbital Observations of Large-Amplitude Kelvin-Helmholtz Waves at Mercury's Magnetopause
We present a survey of Kelvi\ n-Helmholtz (KH) waves at Mercury's magnetopause during MESSENGER's first Mercury year in orb it. The waves were identified on the basis of the well-established sawtooth wave signatures that are associated with non-linear KH vortices at the magnetopause. MESSENGER frequently observed such KH waves in the dayside region of the magnetosphere where the magnetosheath flow velocity is still sub -sonic, which implies that instability growth rates at Mercury's magnetopau~ are much larger than at Earth. We attribute these greater rates to the limited wave energy dissipation in Mercury's highly resistive regolith. The wave amplitude was often on the order of ' 00 nT or more, and the wave periods were - 10- 20 s. A clear dawn-dusk asymmetry is present in the data, in that all of the observed wave events occurred in the post-noon and dusk-side sectors of the magnetopause. This asymmetry is like ly related to finite Larmor-radius effects and is in agreement with results from particle-in-cell simulations of the instability. The waves were observed almost exclusively during periods when the north-south component of the magnetosheath magnetic field was northward, a pattern similar to that for most terrestrial KH wave events. Accompanying plasma measurements show that the waves were associated with the transport of magnetosheath plasma into the magnetosphere.
Sundberg, Torbjorn↗
CFD Simulations of the Supersonic Inflatable Aerodynamic Decelerator (SIAD) Ballistic Range Tests
A series of ballistic range tests were performed on a scaled model of the Supersonic Flight Demonstration Test (SFDT) intended to test the Supersonic Inflatable Aerodynamic Decelerator (SIAD) geometry. The purpose of these experiments were to provide aerodynamic coefficients of the vehicle to aid in mission and vehicle design. The experimental data spans the moderate Mach number range, $3.8-2.0$, with a total angle of attack ($alpha_T$) range, $10o-20o$. These conditions are intended to span the Mach-$alpha$ space for the majority of the SFDT experiment. In an effort to validate the predictive capabilities of Computational Fluid Dynamics (CFD) for free-flight aerodynamic behavior, numerical simulations of the ballistic range experiment are performed using the unstructured finite volume Navier-Stokes solver, US3D. Comparisons to raw vehicle attitude, and post-processed aerodynamic coefficients are made between simulated results and experimental data. The resulting comparisons for both raw model attitude and derived aerodynamic coefficients show good agreement with experimental results. Additionally, near body pressure field values for each trajectory simulated are investigated. Extracted surface and wake pressure data gives further insights into dynamic flow coupling leading to a potential mechanism for dynamic instability.
CFD modeling↗
The ''delta p'' approach from Nike combustion instability
Applicability of delta p approach to study of combustion instability in liquid and solid propellant rocket engines
STAGNATION FLOW↗
CFD Integrated Transition Modeling for High-Speed Flows via Coupled OVERFLOW-LASTRAC Analysis
This work details ongoing efforts at the NASA Langley Research Center to develop and validate a general-use CFD tool that includes built-in predictions of boundary-layer transition in high-speed flows. Existing tools for the coupling of the NASA OVERFLOW structured overset RANS solver and LASTRAC stability analysis code have been extended to capture boundary-layer transition in high-speed flows driven by either Mack’s first-mode or secondmode instabilities and/or crossflow instabilities. The efficacy of this coupled approach has been demonstrated by examining a variety of supersonic and hypersonic test cases for which experimental validation data is available. The intermittency prescription parameters inherited from prior low-speed applications are found to be suitable for some, but not all high-speed flow scenarios. The method is found to be robust for straight cone configurations and improvements necessary to accurately capture transition on geometries with spatially complex amplification factor envelopes with intermediate regions of slow N-factor variation are examined. The automated, coupled analysis is demonstrated for a 3d supersonic test case and found to perform well within the limits of the linear stability analysis on which it relies. Finally, a preliminary investigation of the method’s robustness to non-ideal CFD meshes is conducted.
High-speed flow↗
The Influence of Swirl Brakes and a Tip Discharge Orifice on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Shrouded Centrifugal Pumps
Recent experiments conducted in the Rotor Force Test Facility at the California Institute of Technology have examined the effects of a tip leakage restriction and swirl brakes on the rotordynamic forces due to leakage flows on an impeller undergoing a prescribed circular whirl. The experiments simulate the leakage flow conditions and geometry of the Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump and are critical to evaluating the pump's rotordynamic instability problems. Previous experimental and analytical results have shown that discharge-to-suction leakage flows in the annulus of a shrouded centrifugal pump contribute substantially to the fluid induced rotordynamic forces. Also, previous experiments have shown that leakage inlet (pump discharge) swirl can increase the cross-coupled stiffness coefficient and hence increase the range of positive whirl for which the tangential force is destabilizing. In recent experimental work, the present authors demonstrated that when the swirl velocity within the leakage path is reduced by the introduction of ribs or swirl brakes, then a substantial decrease in both the destabilizing normal and tangential forces could be achieved. Motivation for the present research is that previous experiments have shown that restrictions such as wear rings or orifices at pump inlets affect the leakage forces. Recent pump designs such as the Space Shuttle Alternate Turbopump Design (ATD) utilize tip orifices at discharge for the purpose of establishing axial thrust balance. The ATD has experienced rotordynamic instability problems and one may surmise that these tip discharge orifices may also have an important effect on the normal and tangential forces in the plane of impeller rotation. The present study determines if such tip leakage restrictions contribute to undesirable rotordynamic forces. Additional motivation for the present study is that the widening of the leakage path annular clearance and the installation of swirl brakes in the ATD has been proposed to solve its instability problems. The present study assesses the effect of such a design modification on the rotordynamic forces. The experimental apparatus consists of a solid or dummy impeller, a housing instrumented for pressure measurements, a rotating dynamometer and an eccentric whirl mechanism. The solid impeller is used so that leakage flow contributions to the forces are measured, but the main throughflow contributions are not experienced. The inner surface of the housing has been modified to accommodate meridional ribs or swirl brakes within the leakage annulus. In addition, the housing has been modified to accommodate a discharge orifice that qualitatively simulates one side of the balance piston orifice of the Space Shuttle ATD. Results indicate the detrimental effects of a discharge orifice and the beneficial effects of brakes. Plots of the tangential and normal forces versus whirl ratio show a substantial increase in these forces along with destabilizing resonances at some positive whirl ratios when a discharge orifice is added. When brakes are added, some of the detrimental effects of the orifice are reduced. For the tangential force, a plot versus whirl ratio shows a significant reduction and a destabilizing resonance appears to be eliminated. For the normal force, although the overall force is not reduced, again a destabilizing resonance appears to be eliminated.
Sivo, Joseph M.↗
Morphological and convective instabilities during solidification
Linear stability theory is employed in the present analysis of flow stability between two vertical, infinite, rigid coaxial cylinders at different temperatures. These calculations have been prompted by, and are found to be in general agreement with, experiments on succinonitrile. A long, vertical cylinder sample of this material was heated so that a vertical melt annulus formed between the coaxial heater and the surrounding crystal/melt interface. Above a critical Grashof number of about 200, a helical crystal/melt interface formed which steadily rotated about the cylinder axis and whose wave speed was several orders of magnitude lower than the base flow velocity.
Coriell, S. R.↗
Atomization modeling in a multiphase flow environment and comparison with experiments
An atomization model based on Reitz's instability wave analysis has been implemented into the ARICC3D multiphase CFD combustion code. Preliminary test runs with cold non-evaporating liquid jet and coaxial gas-liquid atomization cases appeared to have verified basic performance of the model, generating realistic-looking sprays. Furthermore, the extended liquid jet is explicitly resolved, and predicted jet lengths agree well with classical correlations. Fair agreement with test data is obtained for predicted spray tip penetrations and liquid mass flux radial distributions, with obvious room for improvement. Some numerical problems also appear to have resulted with the current implementation when low gas Mach number and high liquid velocities are involved.
Liang, P. Y.↗