Caltech Authors
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Repository of works by Caltech published authors.
Mostrando recursos 1 - 20 de 14.621
1.
The dynamic behavior and compliance of a stream of cavitating bubbles - Brennen, C.
The role played by turbopump cavitation in the POGO instability of liquid rockets motivates the present study on the dynamic response of streams of cavitating bubbles to imposed pressure fluctuations. Both quasistatic and more general linearized dynamic analyses are made of the perturbations to a cavitating flow through a region of reduced pressure in which the bubbles first grow and then collapse. The results when reduced coupled with typical bubble number density distribution functions yield compliances which compare favorably with the existing measurements. Since the fluids involved are frequently cryogenic, a careful examination was made of the thermal effects both...
2.
Cavity-flow wall effects and correction rules - Wu, T. Yao-Tsu; Whitney, Arthur K.; Brennen, Christopher
This paper is intended to evaluate the wall effects in the pure-drag case of plane cavity flow past an arbitrary body held in a closed tunnel, and to establish an accurate correction rule. The three theoretical models in common use, namely, the open-wake, Riabouchinsky and re-entrant-jet models, are employed to provide solutions in the form of some functional equations. From these theoretical solutions several different rules for the correction of wall effects are derived for symmetric wedges. These simple correction rules are found to be accurate, as compared with their corresponding exact numerical solutions, for all wedge angles and for...
3.
Bow Wave Dynamics - Waniewski, T. A.; Brennen, C. E.; Raichlen, F.
Experimental studies of air entrainment by breaking waves are essential for advancing the understanding of these flows and creating valid models. The present study used experimental simulations of a ship bow wave to examine its dynamics and air entrainment processes. The simulated waves were created by a deflecting plate mounted at an angle
in a supercritical free-surface flow in a flume. Measurements of the bow wave geometry at two scales and also for a bow wave created by a wedge in a towing tank are presented. Contact line and bow wave profile measurements from the different experiments are compared and demonstrate...
4.
A New Microtensile Tester for the Study of MEMS Materials with the Aid of Atomic Force Microscopy - Chasiotis, Ioannis; Knauss, Wolfgang G.
An apparatus has been designed and implemented to measure the elastic tensile properties (Young's modulus and tensile strength) of surface micromachined polysilicon specimens. The tensile specimens are "dog-bone" shaped ending in a large "paddle" for convenient electrostatic or, in the improved apparatus, ultraviolet (UV) light curable adhesive gripping deposited with electrostatically controlled manipulation. The typical test section of the specimens is 400 µm long with 2 µm x 50 µm cross section. The new device supports a nanomechanics method developed in our laboratory to acquire surface topologies of deforming specimens by means of Atomic Force Microscopy (AFM) to determine (fields...
5.
Observation of Damage Growth in Compressively Loaded Laminates - Chai, H.; Knauss, W. G.; Babcock, C. D.
An experimental program to determine tie phenomenological aspects of composite-panel failure under simultaneous compressive n-plane loading and low-velocity transverse impact [C-75 m/s (0-250 ft/s)] is described. High-speed photography coupled with the shadow-moire technique is used to record the phenomenon of failure propagation. The information gained from these records, supplemented by plate sectioning and observation for interior damage, has provided information regarding the failure-propagation mechanism.
The results show that the failure process can be divided roughly into two phases. In the first phase the plane is impacted, and the resulting response causes interlaminar separation. In the second phase the local damage spreads...
6.
Impeller-Induced Rotor-Dynamic Forces - Acosta, Allan J.; Brennen, Christopher E.; Caughey, Thomas K.
The flow through and around the rotor of a turbomachine exerts a force on the rotor and, hence, rotor shaft and bearing system. In some circumstances this force may lead to excitation of shaft whirl in the direction of impeller rotation. Recent international research of this phenomenon is briefly reviewed; these findings suggest that turbomachines intended to operate well above the first critical speed should take the effect into account.
7.
Analyses of Hydrodynamic Radial Forces on Centrifugal Pump Impellers - Adkins, D. R.; Brennen, C. E.
Hydrodynamic interactions that occur between a centrifugal pump impeller and a volute are experimentally and theoretically investigates. The theoretical analysis considers the inability of the blades to perfectly guide the flow through the impeller, and also includes a quasi-one dimensional treatment of flow in the volute. Flow disturbances at the impeller discharge and the resulting forces are determined by the theoretical model. The model is then extended to obtain the hydrodynamic force perturbations that are caused by the impeller whirling eccentrically in the volute. Under many operating conditions, these force perturbations were found to be destabilizing. Comparisons are made between...
8.
Experiments on Chute Flows of Granular Materials - Ahn, H.; Brennen, C.E.; Sabersky, R. H.
Experiments on continuous, steady flows of granular materials down an inclined channel or chute were made with the object of acquiring information on the rheological properties of the granular material flow and the nature of the boundary condition on the base of the channel. Specifically measurements were made of the mean material velocities and velocity profiles on all boundaries of the flow using cross-correlation of two neighboring fibre-optic displacement probes. The output from these probes was used to obtain (1) the unsteady or random component of the particle velocity in the longitudinal direction and (2) a measure of the volume...
9.
Measurements of Velocity, Velocity Fluctuation, Density, and Stresses in Chute Flows of Granular Materials - Ahn, H.; Brennen, C. E.; Sabersky, R. H.
Experiments on continuous, steady flows of granular materials down an inclined channel or chute have been conducted with the objectives of understanding the characteristics of chute flows and of acquiring information on the rheological behavior of granular material flow. Two neighboring fiber-optic displacement probes provide a means to measure (1) the mead velocity by cross-correlating two signals from the probes, (2) the unsteady or random component of the particle velocity in the longitudinal direction by a procedure of identifying particles, and (3) the mean particle spacing at the boundaries by counting the frequency of passage of the particles. In addition,...
10.
Analysis of the Fully Developed Chute Flow of Granular Materials - Ahn, Hojin; Brennen, Christopher E.; Sabersky, Rolf H.
Existing constitutive relations and governing equations have been used to solve for fully developed chute flows of granular materials. In particular, the results of Lun et al. (1984) have been employed and the boundary value problem has been formulated with two parameters (the coefficient of restitution between particles, and the chute inclination), and three boundary values at the chute base wall, namely the values of solid fraction, granular temperature, and mean velocity at the wall. The boundary value problem has been numerically solved by the "shooting method." The results show the significant role played by granular conduction in determining the...
11.
Rotor-Stator Interaction in a Diffuser Pump - Arndt, N.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.
The interatction between impeller blades and diffuser vanes in a diffuser pump was investigated. Steady and unsteady pressure measurements were taken on the diffuser vanes, and the shroud wall of a vaned and a vaneless diffuser. Steady, unsteady, and ensemble-averaged unsteady data, as well as frequency spectra, are presented. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between impeller blade trailing and diffuser vane leading edge (1.5 and 4.5 percent based on impeller discharge radius). The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at midvane height. The...
12.
Experimental Investigation of Rotor-Stator Interaction in a Centrifugal Pump with Several Vaned Diffusers - Arndt, N.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.
This paper describes an experimental investigation of rotor-stator interaction in a centrifugal pump with several vaned diffusers. Steady and unsteady diffuser vane pressure measurements were made for a two-dimensional test impeller. Unsteady impeller blade pressure measurements were made for a second two-dimensional impeller with blade number and blade geometry identical to the two-dimensional impeller used for the diffuser vane pressure measurements. The experiments were conducted for different flow coefficients and differeent radial gaps between the impeller blade trailing edge and the diffuser vane leading edge (5 and 8 percent of the impeller discharge radius). The largest pressure fluctuations on the...
13.
Observations on Off-Design Flows in Non-Cavitating Axial Flow Inducers - Bhattacharyya, Abhijit; Acosta, Allan J.; Brennen, Christopher E.; Caughey, Thomas K.
This paper describes an investigation of the flows in unshrouded and shrouded inducers which are known to be highly complex, three dimensional flows with real fluid effects. A flow visualization technique using tufts and paint dots was used to study the flows on the blade, hub and housing at off-design flows. It was found that the blade boundary layer flows were attached to the blade surface and that leakage flows were the cause of the upstream swirling backflow in unshrouded inducers. It was also found that shrouded inducers showed flow reversal near the leading edge in addition to the discharge-to-suction...
14.
Rotordynamic Forces in Cavitating Inducers - Bhattacharyya, Abhijit; Acosta, Allan J.; Brennen, Christopher E.; Caughey, Thomas K.
This paper reports an experimental investigation of the rotordynamic forces that occur in a whirling three bladed inducer under the influence of cavitation. The effect of lowering the flow coefficient (and thus causing reverse flows) on these forces were also investigated. The results show the occurrence of large destabilizing peaks in the force tangential to the whirl orbit for positive whirl frequency ratios. Cavitation caused these forces to become destabilizing at both negative and positive whirl frequency ratios. The magnitude of the destabilizing forces increased with decreasing vacitation numbers and flow coefficient. The rotordynamic data obtained do not exhibit the...
15.
Rotordynamic Forces in Cavitating Inducers - Bhattacharyya, A.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.
This paper reports an experimental investigation of rotordynamic forces in a whirling axial flow inducer under the influence of cavitation at various flow coefficients. The results show the occurrence of large destabilizing peaks in the force tagential to the whirl orbit for positive whirl frequency ratios. The magnitude of the destabilizing forces increased with a decrease in cavitation number and flow coefficient. The rotordynamic data obtained do not exhibit quadratic functional behavior normally assumed in many rotordynamic models. Consequently, conventional generalized stiffness, damping, and intertia matrices cannot be determined for the inducer. The results demonstrate the complexity of rotordynamic forces...
16.
Aging and Degradation in Dilute Polymer Solutions - Brennen, C. E.; Gadd, G. E.
This paper describes studies of the properties of dilute solutions of polymers which have been found to reduce friction in turbulent flows. The substances tested, in solution in tap water, were guar gum, polyethylene oxide (Union Carbide 'Polyox' WSR 301) and polyacrylamide (Dow 'Separan' AP 30). It had been previously found that solutions of 'Polyox' and 'Separan' exhibit normal-stress difference effects. Correspondingly for'Polyox' solutions, it has been reported that the pressure increment at the mouth of a pitot tube, or open-ended tube facing into the flow, can be reduced below the value [formula] normal for Newtonian liquids, where [Greek rho]...
17.
Wave Patterns on the Surface of Hydrodynamic Cavities - Brennen, C.
In experiments on cavities behind various axisymmetric headforms, a pattern of waves or ripples with crests parallel to the separation line was observed on the cavity surface just downstream of separation. A theoretical analysis suggests that this pattern results from amplified instabilities in the separated laminar boundary layer on the cavity surface.
18.
Some Cavitation Eexperiments with Dilute Polymer Solutions - Brennen, Christopher
A previous paper (Brennen (1968b)) reported the observation and analysis of wave patterns on the surface of fully developed cavities behind a series of axisymmetric headforms in No.2 water tunnel at Ship Division, NPL. Comparison of theory and experiment appeared to confirm that these waves, which appeared a short distance after separation, grew in amplitude as they were convected downstream and then under certain conditions broke up into turbulence, were the amplified result of a select frequency instability in the separated or cavity surface boundary layer.
The small vertical tunnel (figure 1) was employed to study and extend observation of the...
19.
The Dynamic Balances of Dissolved Air and Heat in Natural Cavity Flows - Brennen, C.
In steady, fully developed and unventilated cavity flows occurring in practice, air (originally dissolved in the water) and heat are diffused through the fluid towards the interface providing a continuous supply of air and vapour to the cavity. This must be balanced by the rate of entrainment of volume of air and vapour away from the cavity in the wake. These equilibria which determine respectively the partial pressure of air within the cavity and the temperature differences involved in the flow are studied in this paper. The particular case of the cavitating flow past a spherical headform has been investigated...
20.
Auto-Oscillation of Cavitating Inducers - Braisted, D. M.; Brennen, C. E.
This paper presents details of measurements on the instability know as auto-oscillation which occurs in systems with cavitating pumps. Specific measurements are made of onset cavitation number and auto-osciallation frequency for a range of inducers. It has been shown that auto-oscillation is a system instability caused by the active dynamic characteristics of the cavitating pump.
A system anslysis is presented which utilized previously measured dynamic transfer functions for the inducers; the resulting predictions of instability are consistent with the observations. Though the onset cavitation number is a function of the entire system it is also show that, given the onset cavitation...
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