Analysis of flexible baffles for damping tank sloshing.
Damping of liquid oscillations in cylindrical tanks, determining rigid and flexible baffle loss coefficients, baffle efficiency and maximum bending stress
LIQUID SLOSHING↗
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Analysis of flexible baffles for damping tank sloshing.
Damping of liquid oscillations in cylindrical tanks, determining rigid and flexible baffle loss coefficients, baffle efficiency and maximum bending stress
OSCILLATING FLOW↗
A theoretical evaluation of rigid baffles in suppression of combustion instability
An analytical technique for the prediction of the effects of rigid baffles on the stability of liquid propellant combustors is presented. This analysis employs both two and three dimensional combustor models characterized by concentrated combustion sources at the chamber injector and a constant Mach number nozzle. An eigenfunction-matching method is used to solve the linearized partial differential equations describing the unsteady flow field for both models. Boundary layer corrections to this unsteady flow are used in a mechanical energy dissipation model to evaluate viscous and turbulence effects within the flow. An integral stability relationship is then employed to predict the decay rate of the oscillations. Results of this analysis agree qualitatively with experimental observations and show that sufficient dissipation exists to indicate that the proper mechanism of baffle damping is a fluid dynamic loss.
Combustion instability↗
Survey of baffle plate samples, specimen machining, and hydrogen measurements
This report outlines preliminary results on the survey and characterization of irradiated baffle plate, baffle former, and flux thimble tube specimens as part of the ongoing investigation into irradiation-induced embrittlement in austenitic stainless steels at ambient (room temperature) conditions. The specimens originated from commercial pressurized water reactor (PWR) components, covering displacement damage doses ranging from approximately 0.065 to 75 dpa. Initial scanning electron microscopy (SEM) surveys revealed that specimen surfaces exhibited fine machining marks and in-service-formed oxide layers on the side surfaces of the analyzed specimens. The oxide layers revealed specific features resembling localized "pitting-like" corrosion. An additional set of specimens representing in-service oxidation is being preserved for future microstructure analysis work. As believed, this will provide additional insights into long-term material degradation in PRWs. Specimen machining challenges emerged due to a complex failure of the electric discharge machining (EDM) system located in hot area. Despite partial restoration, issues persist with the EDM’s secondary power supply, necessitating the exploration of alternative EDM or computer numerical control (CNC) machining approaches to facilitate tensile specimen preparation. Currently, low speed saw cutting is in progress to prepare specimens for hydrogen measurements and general microstructure analysis. The near-term goals include completing tensile specimen machining for advanced mechanical testing and characterizing fracture mechanisms, and stress-corrosion cracking testing, ultimately aiming to identify and mitigate the ambient-condition intergranular cracking through targeted post-irradiation annealing strategies.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Analysis of Deformation and Fracture Mechanisms in the Harvested High-Dose Baffle-Former Bolt with Stress-Corrosion Cracks Formed While in Service
This report presents the results of advanced mechanical testing conducted on miniature tensile specimens excised from an irradiated baffle-former bolt, a commercial pressurized water reactor component. The specimens were extracted from the midsection of the bolt shank, where the estimated damage dose reached 23 displacements per atom. The mechanical testing included the following tests: (1) conventional tensile testing at room temperature, augmented by digital image correlation (DIC) to enable noncontact strain measurements, and (2) in situ tensile testing within a scanning electron microscopy (SEM) instrument equipped with energy-dispersive x-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) detectors to evaluate active deformation and fracture mechanisms. Additionally, SEM fractographic analysis revealed alterations in the fracture mechanism from a predominantly ductile fracture in nonirradiated steel to a mixed fracture mode (still dominating ductile and minor cleavage spots) in irradiated specimens derived from the baffle bolts. The findings indicate a complex strain localization behavior for in-service irradiated steel specimens. Beyond conventional necking at the macro scale and defect-free channel formation at the micro scale, DIC results identified the presence of deformation bands approximately 100 μm in width. These bands consist of chains of grains exhibiting elevated local strain levels and may be considered an intermediate or mesoscale level of strain localization. These bands become discernible near the yield stress as localized hot spots, areas of elevated strain, persisting throughout most of the experiment. The formation of mesoscale deformation bands as a strain localization mechanism may exacerbate the defect-free channel formation in irradiated materials, further promoting irradiation-assisted stress corrosion crack initiation.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Pressures on ring baffles. Damping coefficients for mechanical models of liquid sloshing Quarterly progress report no. 16, 1 Jan. - 31 Mar. 1965
Harmonic analysis of pressures on ring baffles, force measurements for solid and perforated ring baffles, and inertia damping coefficient for model of liquid sloshing - fuel tank
DAMPING↗
Efficient baffle prevents oil backstreaming in diffusion pumps
High vacuum diffusion pump baffle, positioned immediately above pump stack, prevents vaporized pumping oil from entering and contaminating test chamber. Pumping vapors are collected and condensed on the baffle and flow back to pump base reservoir.
Meneghetti, J. R.↗
The variable magnetic baffle as a control device for Kaufman thrusters.
The variable magnetic baffle described in this paper aids in control of electron flow from the hollow cathode plasma into the main discharge region by augmenting the fringe magnetic field which impedes this electron flow in conventionally baffled Kaufman thrusters. A passive, low loss, and automatic control device is obtained by using the discharge current to excite the control winding. Used in conjunction with typical thruster control loops, stable operation has been obtained over a 10:1 throttling range with a 30 cm thruster. Discharge ignition and overcurrent recycling is also facilitated through use of this device in a permanent magnet thruster.
Poeschel, R. L.↗
Ion thruster with a combination keeper electrode and electron baffle
An ion thruster is described in which the cathode front end, surrounded by our insulator, is mounted flush with the front end of the flanged portion of the cathode pole piece. The thruster's baffle positioned in front of the cathode's front end supports the thruster's keeper electrode which is space apart and directed to the cathode's open end. The baffle is at the keeper's electrode potential.
Pawlik, E. V.↗
Analysis of the effects of baffles on combustion instability
An analytical model has been developed for predicting the effects of baffles on combustion instability. This model has been developed by coupling an acoustic analysis of the wave motion within baffled chambers with a model for the oscillatory combustion response of a propellant droplet developed by Heidmann. A computer program was developed for numerical solution of the resultant coupled equations. Diagnostic calculations were made to determine the reasons for the improper prediction. These calculations showed that the chosen method of representing the combustion response was a very poor approximation. At the end of the program, attempts were made to minimize this effect but the model still improperly predicts the stability trends. Therefore, it is recommended that additional analysis be done with an improved approximation.
Oberg, C. L.↗
Electron diffusion through the baffle aperture of a hollow cathode thruster
The use of a hollow cathode in place of an oxide cathode to increase thruster operating lifetimes requires, among other things, the addition of a baffle to restrict the flow of electrons from the hollow cathode. A theoretical model is developed which relates the baffle aperture area of a hollow-cathode thruster to the magnetic flux density and plasma properties in the aperture region, with the result that this model could be used as an aid in thruster design. Extensive Langmuir probing is undertaken to verify the validity of the model and demonstrate its capability. It is shown that the model can be used to calculate the aperture area required to effect discharge operation at a specified discharge voltage and arc current.
Brophy, J. R.↗
Effect of baffle on the asymmetric gravity jitter excited slosh waves in microgravity
The paper investigates the dynamical behavior of fluids affected by asymmetric gravity jitter oscillations, in particular, the effect of surface tension on partially filled rotating fluids in a full-scale Gravity Probe-B Spacecraft dewar tank, with and without the installation of the baffle-board, imposed by time-dependent directions of background gravity. The time-sequence evolution of the 3D behavior of the liquid-vapor interface oscillations resulting in the excitation of large amplitude slosh waves exerted by gravity jitter disturbances are examined. It is shown that the damping effect provided by baffle reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in the liquid-vapor distribution.
Hung, R. J.↗
Comparison of Several Methods of Predicting the Pressure Loss at Altitude Across a Baffled Aircraft-Engine Cylinder
Several methods of predicting the compressible-flow pressure loss across a baffled aircraft-engine cylinder were analytically related and were experimentally investigated on a typical air-cooled aircraft-engine cylinder. Tests with and without heat transfer covered a wide range of cooling-air flows and simulated altitudes from sea level to 40,000 feet. Both the analysis and the test results showed that the method based on the density determined by the static pressure and the stagnation temperature at the baffle exit gave results comparable with those obtained from methods derived by one-dimensional-flow theory. The method based on a characteristic Mach number, although related analytically to one-dimensional-flow theory, was found impractical in the present tests because of the difficulty encountered in defining the proper characteristic state of the cooling air. Accurate predictions of altitude pressure loss can apparently be made by these methods, provided that they are based on the results of sea-level tests with heat transfer.
Neustein, Joseph↗
Reflective Baffles For Telescope
Nonimaged light causing unacceptable heating rejected instead of absorbed. Precise reflective baffles incorporated into reflective telescope to prevent undesired portion of incident light from entering sensitive optical and electronic instruments in focal region of main reflector. In original intended application, telescope and associated instruments placed in geostationary orbit to observe selected area of Earth; undesired light solar reflected from adjacent areas of Earth or coming directly from Sun when line of sight to Sun lies near field of view. Terrestrial optical instruments also improved by installation of reflective baffles.
Hovis, Warren A.↗
Space- and Ground-Based Crystal Growth Using a Baffle (CGB)
The composition of semiconductor crystals produced in space by conventional melt-growth processes (directional solidification and zone melting) is affected by minute levels of residual micro-acceleration, which causes natural convection. The residual acceleration has random magnitude, direction and frequency. Therefore, the velocity field in the melt is apriori unpredictable. As a result, the composition of the crystals grown in space can not be predicted and reproduced. The method for directional solidification with a submerged heater or a baffle was developed under NASA sponsorship. The disk-shaped baffle acts as a partition, creating a small melt zone at the solid-liquid interface. As a result, in ground based experiment the level of buoyancy-driven convection at the interface is significantly reduced. In several experiments with Te-doped GaSb, nearly diffusion controlled segregation was achieved.
Ostrogorsky, A. G.↗
Preservation of Thermal Control Specular Gold Baffle Surface on the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Electronics Compartment (IEC)
Extremely tight thermal control property degradation allowances on the vapor-deposited, gold-coated IEC baffle surface, made necessary by the cryogenic JWST Observatory operations, dictate tight contamination requirements on adjacent surfaces. Theoretical degradation in emittance with contaminant thickness was calculated. Maximum allowable source outgassing rates were calculated using worst case view factors from source to baffle surface. Tight requirements pushed the team to change the design of the adjacent surfaces to minimize the outgassing sources
MonteedeGarcia, Kristina↗
Slosh Baffle Design and Test for Spherical Liquid Oxygen and Liquid Methane Propellant Tank for a Lander
A Vertical Test Bed (VTB) is being developed to investigate exploration technologies with earth-based landing trajectories. During this activity, a concern emerged that the VTB, with large liquid tanks, could experience unstable slosh interaction between the propellant fluid motion and the control system, leading to an investigation of slosh characteristics of the VTB. As such, slosh modeling, analysis and testing were performed, that both verified models and lead to the conclusion that baffles would be required for the full-scale vehicle. Follow-on design and testing supported development of these baffles and measurement of their performance. The majority of the tests conducted, including both subscale and full, involved the use of clear tanks containing water as a reasonable substitute for the cryogenic propellants, though a few tests involved the actual liquid oxygen and methane. Along the way, some unique test and data recording methods were employed to reduce testing complexity and cost.
Strahan, Alan↗
Validation of Slosh Model Parameters and Anti-Slosh Baffle Designs of Propellant Tanks by Using Lateral Slosh Testing
The slosh dynamics of propellant tanks can be represented by an equivalent pendulum-mass mechanical model. The parameters of this equivalent model, identified as slosh model parameters, are slosh mass, slosh mass center of gravity, slosh frequency, and smooth-wall damping. They can be obtained by both analysis and testing for discrete fill heights. Anti-slosh baffles are usually needed in propellant tanks to control the movement of the fluid inside the tank. Lateral slosh testing, involving both random testing and free-decay testing, are performed to validate the slosh model parameters and the damping added to the fluid by the anti-slosh baffles. Traditional modal analysis procedures are used to extract the parameters from the experimental data. Test setup of sub-scale test articles of cylindrical and spherical shapes will be described. A comparison between experimental results and analysis will be presented.
Perez, Jose G.↗