Film-stability in a vertical rotating tube with a core-gas flow
Linear hydrodynamic stability of interface between Newtonian liquid film and core fluid under influence of swirl, core flow, and gravity
Lu, P.-C.↗
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Influence of flow on interface shape stability in low gravity
The objectives are to: (1) Understand the influence in low gravity of flow on interface shape. For example, document and control the influence of axial flow on the Plateau-Rayleigh instability of a liquid bridge; and (2) Extend the ground-based density-matching technique of low gravity simulation to situations with flow; that is, develop Plateau chamber experiments for which flow can be controlled. Containerless containment of liquid by surface tension has broad importance in low gravity. For space vehicles, the behavior of liquid/gas interfaces is crucial to successful liquid management systems. In microgravity science, free interfaces are exploited in various applications. Examples include float-zone crystal growth, phase separation near the critical point of liquid mixtures (spinoidal decomposition) and quenching of miscibility gap molten metal alloys. In some cases, it is desired to stabilize the capillary instability while in others it is desired to induce capillary breakup. In all cases, understanding the stability of interface shape in the presence of liquid motion is central.
Steen, Paul H.↗
Enhancements to Linear Stability-Based, CFD-integrated Transition Prediction for High-Speed Flows
Combining linear stability calculations with computational fluid dynamics (CFD) simulations has great potential for the automated modeling of high-speed flows, especially when adequate information about the configuration and the disturbance environment is available. However, a significant impediment to the applicability of this technique is the lack of an efficient method to calculate the crucial amplification ratio corresponding to the onset of transition in hypersonic flows. This ratio, also known as the "transition N-factor," is dependent upon the freestream disturbance environment as well as the surface properties of the test article. In response to the need for an engineering solution to predict the transition N-factor within conventional hypersonic wind tunnels, this paper presents a data-driven correlation that expands the existing correlations from straight circular cones with a narrow range of half angles to a broader array of axisymmetric configurations. Furthermore, when tested against a chosen dataset that was not used in its calibration, the suggested correlation shows good predictive accuracy with an RMS error of only 6.9%. Although similar accuracy may also be achieved via existing correlations based on similar datasets, predictions based on the proposed correlation have the advantage of not requiring an extensive amount of configuration-specific data. Practical applications often have access to the input parameters needed for this correlation, such as the freestream disturbance intensity, Mach number, and body-based slenderness Reynolds number. Additionally, this correlation outperforms the traditional assumption of a constant N-factor, particularly for configurations with blunted nose geometries. The development of this correlation is grounded in an extensive dataset encompassing conical models with body half-angles varying between 5 degrees and 16 degrees, Mach numbers ranging from 5 to 14, and nosetip-based Reynolds numbers approaching the transition reversal limit for blunt-nosed cones.
CFD↗
Enhancements to Linear Stability-Based, CFD-integrated Transition Prediction for High-Speed Flows
Combining linear stability calculations with computational fluid dynamics (CFD) simulations has great potential for the automated modeling of high-speed flows, especially when adequate information about the configuration and the disturbance environment is available. However, a significant impediment to the applicability of this technique is the lack of an efficient method to calculate the crucial amplification ratio corresponding to the onset of transition in hypersonic flows. This ratio, also known as the "transition N-factor," is dependent upon the freestream disturbance environment as well as the surface properties of the test article. In response to the need for an engineering solution to predict the transition N-factor within conventional hypersonic wind tunnels, this paper presents a data-driven correlation that expands the existing correlations from straight circular cones with a narrow range of half angles to a broader array of axisymmetric configurations. Furthermore, when tested against a chosen dataset that was not used in its calibration, the suggested correlation shows good predictive accuracy with an RMS error of only 6.9%. Although similar accuracy may also be achieved via existing correlations based on similar datasets, predictions based on the proposed correlation have the advantage of not requiring an extensive amount of configuration-specific data. Practical applications often have access to the input parameters needed for this correlation, such as the freestream disturbance intensity, Mach number, and body-based slenderness Reynolds number. Additionally, this correlation outperforms the traditional assumption of a constant N-factor, particularly for configurations with blunted nose geometries. The development of this correlation is grounded in an extensive dataset encompassing conical models with body half-angles varying between 5 degrees and 16 degrees, Mach numbers ranging from 5 to 14, and nosetip-based Reynolds numbers approaching the transition reversal limit for blunt-nosed cones.
CFD↗
Three-Dimensional Navier-Stokes Simulation of Space Shuttle Main Propulsion 17-inch Disconnect Valves
A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle external tank/orbiter propellant feed line disconnect flapper valves with upstream elbows. The Navier-Stokes code, INS3D, is modified to handle interior obstacles and a simple turbulence model. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 million. The predicted hydrodynamical stability of the flappers correlates well with the measurements.
Kandula, M.↗
Stability of two fluid wheel flows with an imposed uniform axial magnetic field
Stability of incompressible two-fluid wheel flows with imposed uniform axial magnetic field for gas core nuclear rockets
Monnin, C. F.↗
Theoretical analyses of Baroclinic flows
A stability analysis of a thin horizontal rotating fluid layer which is subjected to arbitrary horizontal and vertical temperature gradients is presented. The basic state is a nonlinear Hadley cell which contains both Ekman and thermal boundary layers; it is given in closed form. The stability analysis is based on the linearized Navier-Stokes equations, and zonally symmetric perturbations in the form of waves propagating in the meridional direction are considered. Numerical methods were used for the stability problem. It was found that the instability sets in when the Richardson number is close to unity and that the critical Richardson number is a non-monotonic function of the Prandtl number. Further, it was found that the critical Richardson number decreases with increasing Ekman number until a critical value of the Ekman number is reached beyond which the fluid is stable.
Antar, B.↗
Compressible and incompressible fluid seals: Influence on rotordynamic response and stability
The flow field inside a whirling annular seal operating a Reynolds numbers of 12,000 and 24,000 and a Taylor number of 6,600 was measured. The rotor was mounted eccentric (50 percent) upon the facilities shaft which resulted in a circular orbit at a whirl ratio of 1.0. Three papers which summarize the work were written and are presented. Addition measurements were performed for the annular seal operating at an eccentricity ratio of 10 percent for Re = 24,000 and Ta = 6,600. A labyrinth seal was also installed into the facility and operated at an eccentricity ratio of 50 percent at the same Reynolds and Taylor numbers. These data are currently being reduced and analyzed.
Thames, Howard D.↗
The stability of dissipative magnetohydrodynamic shear flow in a parallel magnetic field
The linear stability properties of dissipative field-aligned shear flow are described analytically. The results are used to calculate the decay bounds of linearized perturbations occurring in unbounded planes of Couette flow in a parallel magnetic field. It is shown that the perturbations associated with small-amplitude localized disturbances may take the form of rolls along the shear, and exhibit ordinary potential decay, while misaligned perturbations exhibit enhanced decay in the presence of dissipation. A decay criterion is established for MHD shear flow in an accretion disk on the basis of the analytical results.
Lerner, J.↗
Advanced stability theory analyses for laminar flow control
Recent developments of the SALLY computer code for stability analysis of laminar flow control wings are summarized. Extensions of SALLY to study three dimensional compressible flows, nonparallel and nonlinear effects are discussed.
Orszag, S. A.↗
Linear stability analysis of spherical accretion flows onto compact objects
The steady state structure and linear stability of spherical accretion flows onto compact objects are investigated over a wide range of accretion rates (ARs) for a variety of cooling functions as a function of the ratio of specific heats (gamma). Both radial and nonradial shock perturbations are considered. The flows become more extended as AR decreases. The cooling function has a significant effect on the extended structure of settling solutions with gamma = 5/3. In contrast, the extended structure of settling solutions with gamma = 4/3 is nearly independent of the form of the cooling function. For both gamma = 4.3 and gamma = 5.3, radial shock oscillation in the fundamental and first overtone modes are destabilized in spherically extended accretion envelopes. The application of these results to postsupernova neutron star accretion flows and to luminosity oscillations in AM Her objects are discussed.
Houck, John C.↗
Stability of low-speed reacting flows
Small perturbation, linear, inviscid stability theory is developed and applied to coflowing chemically reacting jets. A necessary condition for the existence of axisymmetric and azimuthal instabilities is derived. The eigenfunction structure provides considerable insight into the underlying physical mechanism. In nonpremixed cases, high temperature tends to occur in regions where the shear layer tries to roll up; this reduces the available momentum, suppressing the growth of instabilties. It is found that chemical reaction during the growth of instabilities is unimportant, suggesting that this effect could be ignored in a viscous theory. Both nonpremixed and premixed flames in axisymmetric shear layers are generally more stable to small perturbations than in the corresponding cold case. However, while for nonpremixed flames the frequency of the most amplified wave decreases with increasing heat release, the opposite occurs for premixed cases.
Mahalingham, S.↗
Stability of erythrocyte suspensions layered on stationary and flowing liquids
The apparent stability of erythrocyte suspensions layered on stationary and flowing Ficoll solutions was studied considering the effects of particle concentration, type and size, and the different flow rates of the particle suspensions and chamber liquid. The data from the flowing system were empirically fitted and, when extrapolated to zero chamber liquid flow rate, gave values comparable to the data from the stationary system, thus confirming the validity of the data and our approach to obtain that data.
Omenyi, S. N.↗
Flow Analysis of Space Shuttle Feed Line 17-inch Disconnect Valve
A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle External Tank/Orbiter propellant feed line disconnect flapper valves with upstream elbows. The full Navier-Stokes code, INS3D, is modified to handle interior obstacles. Grids are generated by SVTGD3D code. Two dimensional initial grids in the flow cross section with and without the flappers are improved by elliptic smoothing to provide better orthogonality, clustering and smoothness to the three dimensional grid. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 x 10(exp 6). The results will serve as a guide to improved design and enhanced testing of the disconnect.
Kandula, Max↗
Stabilization of Taylor-Couette flow due to time-periodic outer cylinder oscillation
The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is driven sinusoidally in time with zero mean rotation. This configuration was studied experimentally by Walsh and Donnelly. The critical Reynolds numbers calculated from linear stability theory agree well with the experimental values, except at large modulation amplitudes and small frequencies. The theoretical values are obtained using Floquet theory implemented in two distinct approaches: a truncated Fourier series representation in time, and a fundamental solution matrix based on a Chebyshev pseudospectral representation in space. For large amplitude, low frequency modulation, the linear eigenfunctions are temporally complex, consisting of a quiescent region followed by rapid change in the perturbed flow velocities.
Murray, B. T.↗
Stability of a nonorthogonal stagnation flow to three-dimensional disturbances
A similarity solution for a low Mach number nonorthogonal flow impinging on a hot or cold plate is presented. For the constant density case, it is known that the stagnation point shifts in the direction of the incoming flow and that this shift increases as the angle of attack decreases. When the effects of density variations are included, a critical plate temperature exists; above this temperature the stagnation point shifts away from the incoming stream as the angle is decreased. This flowfield is believed to have application to the reattachment zone of certain separated flows or to a lifting body at a high angle of attack. Finally, the stability of this nonorthogonal flow to self similar, 3D disturbance is examined. Stability properties of the flow are given as a function of the parameters of this study; ratio of the plate temperature to that of the outer potential flow and angle of attack. In particular, it is shown that the angle of attack can be scaled out by a suitable definition of an equivalent wavenumber and temporal growth rate, and the stability problem for the nonorthogonal case is identical to the stability problem for the orthogonal case.
Lasseigne, D. G.↗
On stability of premixed flames in stagnation - Point flow
A quantitative description of flame stabilization in stagnation-point flow is proposed. Asymptotic and stability analyses are made for a flame model where the density of the gas is assumed to be constant and the reaction zone is assumed to be narrow and concentrated over the flame front. It is shown that, if blowing is sufficiently strong, the corrugations disappear and a plane flame results. The phenomena cannot be fully described by means of classical linear stability analysis.
Sivashinsky, G. I.↗
Film stability in a vertical rotating tube with a core-gas flow.
The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Sarma, G. S. R.↗