scholarly journals The impulsive motion of a liquid resulting from a particle collision

1998 ◽  
Vol 375 ◽  
pp. 345-361 ◽  
Author(s):  
R. ZENIT ◽  
M. L. HUNT
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Pressure Pulse ◽  
Fluid Pressure ◽  
Particle Diameter ◽  
Digital Camera ◽  
Particle Collision ◽  
High Frequency Response ◽  
Response Pressure ◽  
Impulse Pressure

When two particles collide in a liquid, the impulsive acceleration due to the rebound produces a pressure pulse that is transmitted through the fluid. Detailed measurements were made of the pressure pulse and the motion of the particles by generating controlled collisions with an immersed dual pendulum. The experiments were performed for a range of impact velocities, angles of incidence, and distances between the wall and the pairs of particles. The radiated fluid pressure was measured using a high-frequency-response pressure transducer, and the motion of the particles was recorded using a high-speed digital camera. The magnitude of the impulse pressure was found to scale with the particle velocity, the particle diameter and the density of the fluid. Additionally, a model is proposed to predict the impulse field in the fluid based on the impulse pressure theory. The model agrees well with the experimental measurements.

Mechanics of Immersed Particle Collisions

1999 ◽  
Vol 121 (1) ◽  
pp. 179-184 ◽  
Author(s):  
Roberto Zenit ◽  
Melany L. Hunt
Keyword(s):  
High Speed ◽  
Control Volume ◽  
Particle Diameter ◽  
Digital Camera ◽  
Pressure Profile ◽  
Stokes Number ◽  
Elastic Collision ◽  
Initial Kinetic Energy ◽  
Fluid Inertia ◽  
Particle Collisions

The present work investigates the mechanics of particle collisions submerged in a liquid using a simple pendulum experiment. Particle trajectories for different particles in water are measured using a high-speed digital camera and the magnitude of the collision is recorded using a high-frequency-response pressure transducer at the colliding surface. The particle deceleration occurs at distances less than half a particle diameter from the wall. The measured collision impulse increases with impact velocity and particle mass. Comparisons are drawn between the measured pressures and the predictions of basic impact mechanics assuming a perfectly elastic collision. A control-volume model is proposed that accounts for the fluid inertia and viscosity. When a particle approaches a planar surface or another particle, the fluid is squeezed prior to contact, reducing the initial kinetic energy and decelerating the particle. The pressure profile is integrated over the surface of the particle to obtain a force that is a function of the initial particle Reynolds number, Reo, and the ratio of the densities of the particle and fluid phases, ρp/ρf. The model predicts a critical Stokes number at which the particle reaches the wall with zero velocity. Comparisons between the proposed model and the experimental measurements show qualitative agreement.

Unsteady Viscous Flow in a High-Speed Core Compressor

1992 ◽  
Vol 114 (2) ◽  
pp. 287-294 ◽  
Author(s):  
M. A. Cherrett ◽  
J. D. Bryce
Keyword(s):  
High Speed ◽  
Secondary Flows ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Unsteady Viscous Flow ◽  
Novel Method ◽  
Multistage Compressor ◽  
Response Pressure ◽  
Random Fluctuations ◽  
Unsteady Pressure Measurements

A probe incorporating a miniature high-frequency response pressure transducer has been traversed behind the first three stages of a high-speed multistage compressor operating at throttle settings corresponding to near choke, peak efficiency, and near surge. A novel method of compensating for transducer temperature sensitivity was employed. Consequently, time-averaged pressures derived from the transducer were found to be in good agreement with pneumatic pressure measurements. Analysis of the unsteady pressure measurements revealed both the periodic and random fluctuations in the flow field. This provided information on rotor-rotor interaction effects and the nature of viscous blade wake and secondary flows in each stage.

Spatial Correlation Based Stall Inception Analysis

2007 ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris
Keyword(s):  
Spatial Correlation ◽  
High Speed ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Fourier Decomposition ◽  
Stall Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Wide Range ◽  
Response Pressure

Investigations of stall inception and compressor pre-stall behavior have used a variety of techniques to make inferences about the mechanisms of rotating stall inception. Many of these techniques utilized data from arrays of circumferentially spaced hot-wires or high frequency response pressure transducers. This paper presents results from the application of several typical analysis techniques to the interpretation of unsteady casing pressure measurements recorded during two representative stall event in a high-speed axial compressor stage. Results from visual pressure trace inspection, spatial Fourier decomposition, wavelet filtering, and traveling wave energy techniques are presented and compared. The effects of measurement and analysis parameters are also briefly discussed. A new analysis technique based on windowed two-point spatial correlation between adjacent stall inception sensors is described. The method was found to provide both spatial and temporal information about rotating features in the compressor flow and is insensitive to low pass filtering and parameter selection over a wide range of values. It was also found to be valuable for analysis of both pre-stall and stall inception behavior.

Experimental Study of Surge Precursors in a High-Speed Multistage Compressor

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Nicolas Courtiade ◽  
Xavier Ottavy
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Rotation Speed ◽  
Characteristic Line ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Stable Operating ◽  
Variable Duration ◽  
Multistage Compressor ◽  
Operating Points

Pressure measurements using high frequency response sensors have been carried out on the third rotor of the 3.5-stage high speed compressor CREATE (rotation speed: 11,543 RPM, Rotor 1 tip speed: 313 m/s) over the complete characteristic line and during the surge transient. Precursors to the instabilities occurring near surge are observable at stable operating points. Just before surge, these precursors characterized as rotating disturbances grow in amplitude and provoke the onset a stall cell after a variable duration, which finally triggers surge. This paper presents a detailed analysis of the phenomena of rotating instabilities and surge transient and shows that it is possible to develop an antisurge active control system based on the early detection of the precursors.

An evaluation technique for high-frequency dynamic behavior of a sandwich microcantilever beam

2017 ◽  
Vol 21 (3) ◽  
pp. 1133-1149
Author(s):  
Yun Young Kim
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Beam Theory ◽  
Tone Burst ◽  
Ultrasonic Frequency ◽  
Vibration Modes ◽  
High Frequency Response ◽  
Frequency Regime ◽  
Contact Transducer ◽  
Microcantilever Beam

A method was developed to measure the first- and second-order vibration modes in a sandwich microcantilever beam oscillating in the megahertz frequency regime in the present study. Taking advantage of the ultrasonic frequency, a test platform was developed to induce free vibration of the microcantilever using a high-power radio frequency pulser that transmits tone burst signals to a contact transducer, and the resonant frequencies of the microcantilever were measured using a laser-optic interferometer. Results show that the microcantilever’s vibration above 8 MHz can be successfully detected, and its vibration modes were identified through a theoretical study based on the Euler–Bernoulli beam theory and a numerical analysis using the finite element method. The present study proposes a facile and effective way to actuate a high-speed sandwich microcantilever and detect its high-frequency response so that the technique can be employed to study the characteristics of micro- and nanomechanical sandwich structures and their properties.

scholarly journals Unsteady Viscous Flow in a High Speed Core Compressor

1991 ◽  
Author(s):  
M. A. Cherrett ◽  
J. D. Bryce
Keyword(s):  
High Speed ◽  
Secondary Flows ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Unsteady Viscous Flow ◽  
Novel Method ◽  
Multistage Compressor ◽  
Response Pressure ◽  
Random Fluctuations ◽  
Unsteady Pressure Measurements

A probe incorporating a miniature high-frequency response pressure transducer has been traversed behind the first three stages of a high-speed multistage compressor operating at throttle settings corresponding to near choke, peak efficiency and near surge. A novel method of compensating for transducer temperature sensitivity was employed. Consequently, time-averaged pressures derived from the transducer were found to be in good agreement with pneumatic pressure measurements. Analysis of the unsteady pressure measurements revealed both the periodic and random fluctuations in the flowfield. This provided information on rotor-rotor interaction effects and the nature of viscous blade wake and secondary flows in each stage.

scholarly journals A High-Frequency-Response Pressure Probe for the Measurement of Unsteady Flow Between Two Rotors in a Hydrodynamic Turbomachine

1996 ◽  
Author(s):  
C. Achtelik ◽  
J. Eikelmann
Keyword(s):  
Unsteady Flow ◽  
Frequency Response ◽  
High Frequency ◽  
Torque Converter ◽  
Pressure Probe ◽  
Ensemble Averaging ◽  
Probe Diameter ◽  
High Frequency Response ◽  
Single Sensor ◽  
Response Pressure

A new, specially-developed high-frequency-response pressure probe was used to measure the unsteady flow in the interaction region between the pump and the turbine in a hydrodynamic torque converter. In order to reduce the probe diameter, a single-hole, single-sensor cylindrical probe (⌀=1.33mm) was developed, to replace the standard multi-hole probe. The smaller the probe the higher the accuracy in unsteady flow. Therefore this is an improvement over three-hole probe. Three-hole probe measurements were simulated by recording data in three different angular positions. The time variable velocity vectors were determined using the probe’s calibration coefficients and the knowledge of the rotor positions (measured by angle-encoders) for every measurement value. During the data processing, a double ensemble averaging was carried out, taking into account the positions of the pump and the turbine.

Experimental Study of Surge Precursors in a High-Speed Multistage Compressor

2012 ◽  
Author(s):  
Nicolas Courtiade ◽  
Xavier Ottavy
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Rotation Speed ◽  
Critical Size ◽  
Rotating Stall ◽  
Characteristic Line ◽  
High Frequency Response ◽  
Stable Operating ◽  
Multistage Compressor ◽  
Operating Points

Pressure measurements using high frequency response sensors have been carried out on the 3rd rotor of the 3 1/2-stage high speed compressor CREATE (rotation speed: 11543 RPM, Rotor 1 tip speed: 313 m/s), over the complete characteristic line and during the surge transient. It seems that precursors to the instabilities occurring near surge are observable at stable operating points. Just before the surge, these precursors characterized as rotating disturbances transition smoothly to part span rotating stall cells, and bring the machine to surge as they grow and reach a critical size: this paper presents a detailed analysis of the phenomena of rotating stall and surge transient and shows that it is possible to develop an anti-surge active control system based on the early detection of the precursors.

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