SEARCH · Engineering Papers

Results for “cavitation bubbles”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2

All sources NASA NTRS DOE OSTI

NASA NTRS1972

Investigation of characteristics of feed system instabilities

The relationship between the structural and feed system natural frequencies in structure-propulsion system coupled longitudinal oscillations (pogo) is investigated. The feed system frequencies are usually very dependent upon the compressibility (compliance) of cavitation bubbles that exist to some extent in all operating turbopumps. This document includes: a complete review of cavitation mechanisms; development of a turbopump cavitation compliance model; an accumulation and analysis of all available cavitation compliance test data; and a correlation of empirical-analytical results. The analytical model is based on the analysis of flow relative to a set of cascaded blades, having any described shape, and assumes phase changes occur under conditions of isentropic equilibrium. Analytical cavitation compliance predictions for the J-2 LOX, F-1 LOX, H-1 LOX and LR87 oxidizer turbopump inducers do not compare favorably with test data. The model predicts much less cavitation than is derived from the test data. This implies that mechanisms other than blade cavitation contribute significantly to the total amount of turbopump cavitation.

Vaage, R. D.↗

NASA NTRS1988

Elasticity effects on cavitation in a squeeze film damper undergoing noncentered circular whirl

Elasticity of the liner and its effects on cavitation were numerically determined for a squeeze film damper subjected to dynamic loading. The loading was manifested as a prescribed motion of the rotor undergoing noncentered circular whirl. The boundary conditions were implemented using Elrod's algorithm which conserves lineal mass flux through the moving cavitation bubble as well as the oil film region of the damper. Computational movies were used to analyze the rapidly changing pressures and vapor bubble dynamics throughout the dynamic cycle for various flexibilities in the damper liner. The effects of liner elasticity on cavitation were only noticeable for the intermediate and high values of viscosity used in this study.

Brewe, David E.↗

NASA NTRSDate not supplied

Cavitation Effects on the Structural Dynamics of Turbomachinery Components

The structural integrity of inducer and impeller blades in rocket engine turbomachinery must be evaluated in the face of complex excitation mechanisms including fluctuating pressures due to cavitation. Cavitation occurs when the local fluid pressure drops below the vapor pressure, causing the formation of vapor-filled bubbles. Cavitation can exist to various extents within the typical operating range of rocket engine turbopumps. Despite recent progress towards reducing uncertainties in structural dynamic models of turbomachinery components, the extent to which pump cavitation affects the structural dynamic properties (i.e., natural frequencies, damping, and mode shapes) of inducer and impeller blades remains largely unknown. To study the structural dynamic effects of cavitating flows, experiments are conducted in a high-speed water tunnel. The test articles mimic a single inducer blade that is unwrapped from the hub, thus resembling a low aspect ratio cantilevered plate. To induce cavitation, the plates are oriented at a non-zero angle of attack and have rough strips near their leading edges. To control the extent of cavitation, the static pressure of the water tunnel is controlled between roughly 0.5 and 1.5 atm. A high-speed camera is used to quantify the coverage of the cavitations heet. The sheet coverage is then correlated to changes in fluid-added mass and hydroelstic damping. In addition, a corresponding two-way coupled CFD/FE model is under development for test/analysis correlation.

Ben Davis↗

NASA NTRSDate not supplied

Cavitation Effects on the Structural Dynamics of Turbomachinery Components

The structural integrity of inducer and impeller blades in rocket engine turbomachinery must be evaluated in the face of complex excitation mechanisms including fluctuating pressures due to cavitation. Cavitation occurs when the local fluid pressure drops below the vapor pressure, causing the formation of vapor-filled bubbles. Cavitation can exist to various extents within the typical operating range of rocket engine turbopumps. Despite recent progress towards reducing uncertainties in structural dynamic models of turbomachinery components, the extent to which pump cavitation affects the structural dynamic properties (i.e., natural frequencies, damping, and mode shapes) of inducer and impeller blades remains largely unknown. To study the structural dynamic effects of cavitating flows, experiments are conducted in a high-speed water tunnel. The test article is a low aspect ratio cantilevered plate, thus mimicing a single inducer blade that is unwrapped from its hub. The test article is oriented at zero angle of attack and has a triangular trip at its leading edge to induce cavitation. To change the extent of cavitation, the static pressure of the water tunnel is controlled. A high-speed camera is used to quantify the coverage of the cavitation sheet.

Fluid-Structure Interaction↗

NASA NTRSDate not supplied

Cavitation Effects on the Structural Dynamics of Turbomachinery Components

The structural integrity of inducer and impeller blades in rocket engine turbo machinery must be evaluated in the face of complex excitation mechanisms including fluctuating pressures due to cavitation. Cavitation occurs when the local fluid pressure drops below the vapor pressure, causing the formation of vapor-filled bubbles. Cavitation can exist to various extents within the typical operating range of rocket engine turbo pumps. Despite recent progress towards reducing uncertainties in structural dynamic models of turbo machinery components, the extent to which pump cavitation affects the structural dynamic properties (i.e., natural frequencies, damping, and mode shapes) of inducer and impeller blades remains largely unknown. To study the structural dynamic effects of cavitating flows, experiments are conducted in a high-speed water tunnel. The test article is a low aspect ratio cantilevered plate, thus mimicing a single inducer blade that is unwrapped from its hub. The test article is oriented at zero angle of attack and has a triangular trip at its leading edge to induce cavitation. To change the extent of cavitation, the static pressure of the water tunnel is controlled. A high-speed camera is used to quantify the coverage of the cavitation sheet.

Structural Dynamics↗

NASA NTRS1962

Observations on Cavitation Damage in a Flowing System

Cavitation damage to specimens of stainless steel, carbon steel, aluminum, and plexiglas, placed in a cavitating venturi using water and mercury as test fluids is mostly in the form of irregularly shaped pits which do not change with additional exposure to the cavitating field within the limited durations utilized. The rate of damage is very high initially, decreases for a relatively short period of time, then increases again up to the maximum test durations of 150 hours with water and 270 hours with mercury. Observation of damage effects by several independent techniques, using a variety of specimen materials, with two different fluids under various fluid dynamic conditions, leads to a suggested correlating model in terms of the cavitation bubble density and energy and specimen material strength.

VENTURI TUBE↗

NASA NTRS1982

High-speed motion picture camera experiments of cavitation in dynamically loaded journal bearings

A high-speed camera was used to investigate cavitation in dynamically loaded journal bearings. The length-diameter ratio of the bearing, the speeds of the shaft and bearing, the surface material of the shaft, and the static and dynamic eccentricity of the bearing were varied. The results reveal not only the appearance of gas cavitation, but also the development of previously unsuspected vapor cavitation. It was found that gas cavitation increases with time until, after many hundreds of pressure cycles, there is a constant amount of gas kept in the cavitation zone of the bearing. The gas can have pressures of many times the atmospheric pressure. Vapor cavitation bubbles, on the other hand, collapse at pressures lower than the atmospheric pressure and cannot be transported through a high-pressure zone, nor does the amount of vapor cavitation in a bearing increase with time. Analysis is given to support the experimental findings for both gas and vapor cavitation.

Jacobson, B. O.↗

NASA NTRS1983

High-speed motion picture camera experiments of cavitation in dynamically loaded journal bearings

Hamrock, B. J.↗

DOE OSTI2024

Kelvin-Helmholtz instability as one of the key features for fast and efficient emulsification by hydrodynamic cavitation

The paper investigates the oil–water emulsification process inside a micro-venturi channel. More specifically, the possible influence of Kelvin-Helmholtz instability on the emulsification process. High-speed visualizations were conducted inside a square venturi constriction with throat dimensions of 450 µm by 450 µm, both under visible light and X-Rays. We show that cavity shedding caused by the instability results in the formation of several cavity vortices. Their rotation causes the deformation of the oil stream into a distinct wave-like shape, combined with fragmentation into larger drops due to cavitation bubble collapse. Later on, the cavity collapse further disperses the larger drops into a finer emulsion. Thus, it turns out that the Kelvin-Helmholtz instability is similarly characteristic for hydrodynamic cavitation emulsification inside a microchannel as is the Rayleigh-Taylor instability for acoustically driven emulsion formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1980

Dynamics of cavitating cascades

The unsteady dynamics of cavitating cascades and inducer pumps were studied with a view to understanding (and possibly predicting) the dynamic characteristics of these devices. The chronology of the research is summarized as well as the final conculsions for each task. The construction of a dynamic pump test facility and its use in making experimental measurements of the transfer function is described as well as tests conducted using a scale model of the low pressure liquid oxygen turbopump inducer in the shuttle main engine. Auto-oscillation and unsteady inlet flow characteristics are discussed in addition to blade cavity influence and bubbly cavitation.

Brennen, C. E.↗

NASA NTRS2012

Investigation of Turbulent Tip Leakage Vortex in an Axial Water Jet Pump with Large Eddy Simulation

Detailed steady and unsteady numerical studies were performed to investigate tip clearance flow in an axial water jet pump. The primary objective is to understand physics of unsteady tip clearance flow, unsteady tip leakage vortex, and cavitation inception in an axial water jet pump. Steady pressure field and resulting steady tip leakage vortex from a steady flow analysis do not seem to explain measured cavitation inception correctly. The measured flow field near the tip is unsteady and measured cavitation inception is highly transient. Flow visualization with cavitation bubbles shows that the leakage vortex is oscillating significantly and many intermittent vortex ropes are present between the suction side of the blade and the tip leakage core vortex. Although the flow field is highly transient, the overall flow structure is stable and a characteristic frequency seems to exist. To capture relevant flow physics as much as possible, a Reynolds-averaged Navier-Stokes (RANS) calculation and a Large Eddy Simulation (LES) were applied for the current investigation. The present study reveals that several vortices from the tip leakage vortex system cross the tip gap of the adjacent blade periodically. Sudden changes in local pressure field inside tip gap due to these vortices create vortex ropes. The instantaneous pressure filed inside the tip gap is drastically different from that of the steady flow simulation. Unsteady flow simulation which can calculate unsteady vortex motion is necessary to calculate cavitation inception accurately even at design flow condition in such a water jet pump.

Hah, Chunill↗

DOE OSTI2023

Dynamics of oil–water interface at the beginning of the ultrasonic emulsification process

A lot of effort has been dedicated in recent years towards understanding the basics of cavitation induced emulsification, mainly in the form of single cavitation bubbles. Regarding bulk acoustic emulsification, a lot less research has been done. In our here presented work we utilize advanced high-speed observation techniques in visible light and X-Rays to build upon that knowledge and advance the understanding of bulk emulsion preparation. During research we discovered that emulsion formation has an acute impact on the behavior of the interface and more importantly on its position relative to the horn, hence their interdependence must be carefully studied. We did this by observing bulk emulsification with 2 cameras simultaneously and corroborating these measurements with observation under X-Rays. Since the ultrasonic horns location also influences interface behavior, we shifted its initial position to different locations nearer to and further away from the oil–water interface in both phases. We found that a few millimeters distance between the horn and interface is not enough for fine emulsion formation, but that they must be completely adjacent to each other, with the horn being located inside the oil–water interface. We also observed some previously undiscovered phenomena, such as the splitting of the interface to preserve continuous emulsion formation, climbing of the interface up the horn and circular interface protrusions towards the horn forming vertical emulsion streams. Interestingly, no visible W/O emulsion was ever formed during our experiments, only O/W regardless of initial horn position.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Data-driven picosecond X-ray imaging for quantitative plasma-induced shock characterization

Imaging dynamic events, especially shockwave behavior, is key to advancing high-energy-density (HED) research. Recent advances in fourth- and fifth-generation X-ray light sources allow for high-resolution imaging of fast phenomena, but limited beam time necessitates maximizing data acquisition. We present a benchtop-scale pulsed plasma device submerged in liquid heptane, capable of generating dynamic events at rates exceeding 10 Hz, supporting the field’s data-driven goals by producing large, high-quality imaging datasets. Using X-ray phase contrast imaging (XPCI) at the Advanced Photon Source, we imaged weak shockwaves (Mach ~ 1.2) in heptane interacting with plasma-induced cavitation bubbles, causing deviation from Rankine-Hugoniot behavior; to our knowledge, this represents the first direct imaging of such interaction. Our quantitative analysis offers insight into weak shock phenomena and energy-focusing applications in pulsed plasmas. These results highlight the potential for large datasets to advance dynamic HED research at current light source facilities, and have implications for fields such as inertial confinement fusion, plasma-enhanced chemical processing, and biomedical applications.

36 MATERIALS SCIENCE↗

NASA NTRS1971

Ultrasonic metal etching for metallographic analysis

Ultrasonic etching delineates microstructural features not discernible in specimens prepared for metallographic analysis by standard chemical etching procedures. Cavitation bubbles in ultrasonically excited water produce preferential damage /etching/ of metallurgical phases or grain boundaries, depending on hardness of metal specimens.

Young, S. G.↗

NASA NTRS1974

Cracking and reformation of saturated hydrocarbons by ultrasound in the presence of water

The exposure of saturated hydrocarbons to ultrasound (800 kHz, 6 W/sq cm) in the presence of water results in: (1) cleavage of the carbon chain, producing saturated and unsaturated hydrocarbons with a lower number of carbons than the initial hydrocarbon (cracking); and (2) recombination after cleavage, producing saturated and unsaturated hydrocarbons with a higher number of carbons than the initial hydrocarbon (reformation). The addition of argon facilitates these phenomena. The effects are attributed to a homolytic (radical) mechanism occurring within the cavitation bubbles under the effects of microsparks.

Prudhomme, M. R. O.↗

NASA NTRS1983

Vapor Cavitation in Dynamically Loaded Journal Bearings

High speed motion camera experiments were performed on dynamically loaded journal bearings. The length to diameter ratio of the bearing, the speed of the roller and the tube, the surface material of the roller, and the static and dynamic eccentricity of the bearing were varied. One hundred and thirty-four cases were filmed. The occurrence of vapor cavitation was clearly evident in the films and figures presented. Vapor cavitation was found to occur when the tensile stress applied to the oil exceeded the tensile strength of the oil or the binding of the oil to the surface. The physical situation in which vapor cavitation occurs is during the squeezing and sliding motion within a bearing. Besides being able to accurately capture the vapor cavitation on film, an analysis of the formation and collapse of the cavitation bubbles and characteristics of the bubble content are presented.

Jacobson, B. O.↗

NASA NTRS1985

Study of journal bearing dynamics using 3-dimensional motion picture graphics

Computer generated motion pictures of three dimensional graphics are being used to analyze journal bearings under dynamically loaded conditions. The motion pictures simultaneously present the motion of the journal and the pressures predicted within the fluid film of the bearing as they evolve in time. The correct prediction of these fluid film pressures can be complicated by the development of cavitation within the fluid. The numerical model that is used predicts the formation of the cavitation bubble and its growth, downstream movement, and subsequent collapse. A complete physical picture is created in the motion picture as the journal traverses through the entire dynamic cycle.

Brewe, D. E.↗

NASA NTRS1993

Adaptation of the Advanced Spray Combustion Code to Cavitating Flow Problems

A very important consideration in turbopump design is the prediction and prevention of cavitation. Thus far conventional CFD codes have not been generally applicable to the treatment of cavitating flows. Taking advantage of its two-phase capability, the Advanced Spray Combustion Code is being modified to handle flows with transient as well as steady-state cavitation bubbles. The volume-of-fluid approach incorporated into the code is extended and augmented with a liquid phase energy equation and a simple evaporation model. The strategy adopted also successfully deals with the cavity closure issue. Simple test cases will be presented and remaining technical challenges will be discussed.

Liang, Pak-Yan↗