scholarly journals Partial Cavities: Pressure Pulse Distribution Around Cavity Closure

1993 ◽  
Vol 115 (2) ◽  
pp. 249-254 ◽  
Author(s):  
Q. Le ◽  
J. P. Franc ◽  
J. M. Michel
Keyword(s):  
Pressure Pulse ◽  
Pulse Height ◽  
Leading Edge ◽  
Limit Case ◽  
Production Rates ◽  
Partial Cavitation ◽  
Pressure Pulses ◽  
Cavity Closure ◽  
Stable Cavity

Pressure pulse height spectra (PPHS) are measured in the case of partial cavitation attached to the leading edge of a hydrofoil. It is shown that the distributions of pressure pulses around cavity closure may significantly differ according to the type of cavity. In the case of a thin, well-closed and stable cavity, the pressure pulse distributions exhibit a strong maximum centered on the visible cavity termination. As the cavity becomes thicker and increasingly open and unsteady, the pressure pulse distribution widens. In the limit case of a cavity periodically shedding bubble clusters, no definite maximum in the pressure pulse distribution is observed. In addition, scaling of pressure pulse height spectra is approached from measurements at two different velocities. It is shown that the pressure pulse height spectra can be correctly transposed from a velocity to another one from two basic scaling rules concerning pulse heights and production rates of bubbles.

A Method for Suppression of Pressure Pulses in Fluid-Filled Piping—Part I: Theoretical Analysis

1992 ◽  
Vol 114 (1) ◽  
pp. 60-65 ◽  
Author(s):  
Y. W. Shin ◽  
A. H. Wiedermann
Keyword(s):  
Theoretical Analysis ◽  
Pressure Pulse ◽  
Substantial Reduction ◽  
Pulse Height ◽  
Practical Interest ◽  
Nondestructive Method ◽  
Trade Off ◽  
Pressure Pulses ◽  
Fluid Jets ◽  
Pressure Surge

A simple, nondestructive method to suppress pressure pulses in fluid-filled piping is theoretically analyzed, and the result provides the basis needed for design and evaluation of a pressure-pulse suppression device based on the proposed theory. The method is based on forming of fluid jets in the event of a pressure surge, such that the pulse height and the energy of the pulse are reduced. The results for pressure pulses in the range of practical interest show that a substantial reduction in the pulse height can be attained, with accompanying reduction of the pulse remaining in the system. The analysis also reveals that a certain amount of trade-off exists in the design of the suppression device; a certain level of pulse energy remaining in the system must be accepted in order to keep the pulse height below a certain level, and vice versa.

Midlatency respiratory-related somatosensory activity and perception of oral pressure pulses in normal humans

2001 ◽  
Vol 90 (6) ◽  
pp. 2048-2056 ◽  
Author(s):  
J. Andrew Daubenspeck ◽  
Harold L. Manning ◽  
John C. Baird
Keyword(s):  
Evoked Potentials ◽  
Pressure Pulse ◽  
Applied Pressure ◽  
Normal Subjects ◽  
Magnitude Production ◽  
Global Field Power ◽  
Oral Pressure ◽  
Pressure Pulses ◽  
Standard Pressure ◽  
The Right

A direct relationship exists within subjects between midlatency features (<100 ms poststimulus) of respiratory-related evoked potentials and the perceived magnitude of applied oral pressure pulse stimuli. We evaluated perception in 18 normal subjects using cross-modality matching of applied pressure pulses via grip force and estimated mechanoafferent activity in these subjects by computing the global field power (GFP) from respiratory-related evoked potentials recorded over the right side of the scalp. We compared across subjects 1) the predicted magnitude production for a standard pressure pulse and 2) the slope (β) and 3) the intercept (INT) of the Stevens power law to the summed GFP over 20–100 ms poststimulus. Both the magnitude production for a standard pressure pulse and the β showed an inverse relationship with the summed GFP over 20–100 ms poststimulus, although there was no relationship between INT and the summed GFP. This may partially reflect characteristics of the mechanosensors and surely includes aspects of cognitive judgment, because we found and corrected for a high correlation between, respectively, β (and INT) for pressure pulses and β (and INT) for estimation of line lengths, a nonrespiratory modality. The relatively shallow, even inverse GFP-to-perception relationship suggests that, despite marked differences in the magnitude of afferent traffic, normal subjects seem to perceive things similarly.

Response of Water-Filled Thin-Walled Pipes to Pressure Pulses: Experiments and Analysis

1980 ◽  
Vol 102 (1) ◽  
pp. 56-61 ◽  
Author(s):  
C. M. Romander ◽  
L. E. Schwer ◽  
D. J. Cagliostro
Keyword(s):  
Pressure Pulse ◽  
Fluid Structure Interaction ◽  
Two Dimensional ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Modeling Techniques ◽  
Pressure Pulses ◽  
Piping Systems ◽  
Dimensional Finite Element ◽  
Thin Walled

Experiments are performed to verify modeling techniques used in fluid-structure interaction codes that predict the response of liquid-filled piping systems to strong pressure pulses. Pressure pulses having a 150-μs rise time, a 2000-psi (13.8 MPa) magnitude, and a 3-ms duration are propagated into straight, water-filled Ni 200 pipes (3-in. (7.6-cm) O.D. 0.065-in. (0.165-cm) wall). Attenuation of the pressure pulse and the strain and deformation along the pipes are measured. The experiments are modeled in WHAM, a two-dimensional, finite-element, compressible fluid-structure interaction code. The experimental and analytical results are discussed in detail and are found to compare favorably.

scholarly journals Cavitation in Turbopumps—Part 2

1962 ◽  
Vol 84 (3) ◽  
pp. 339-349 ◽  
Author(s):  
L. B. Stripling
Keyword(s):  
Correlation Coefficients ◽  
Performance Data ◽  
Inlet Pressure ◽  
Cavitation Performance ◽  
Partial Cavitation ◽  
Cavitation Region ◽  
Cavity Closure ◽  
Correlation Factors ◽  
Mixing Losses

Cavitation performance data of several helical inducers for various flow coefficients are correlated with existing theory. For complete head breakdown conditions, the method employs semiempirical correlation coefficients which supplement the idealized free-streamline solutions obtained by various investigators. Considerations are given to the partial cavitation region utilizing the free-streamline wake solution. The model clearly illustrates the influence of the mixing losses, downstream of the cavity closure, on the inducer’s developed head as the inlet pressure is reduced. With the use of the above semiempirical correlation factors the theory forms a useful basis for design.

On the Phenomenon of Pressure Pulses Reflecting Between Blades of Adjacent Blade Rows of Turbomachines

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Jerzy A. Owczarek
Keyword(s):  
Pressure Pulse ◽  
Physical Phenomenon ◽  
Research Work ◽  
Axial Compressor ◽  
Rotor Blades ◽  
Test Results ◽  
Lehigh University ◽  
Pressure Pulses ◽  
Excitation Frequencies ◽  
Asme Paper

The recently revived interest in “acoustic resonances,” whose details are still not well defined or understood, points to a realization that a new look at some previously unrecognized findings is needed to explain problems encountered in operation of compressors and turbines. The purpose of this paper is to call the attention of the turbomachinery community to an important physical phenomenon of pressure waves in form of pulses, which reflect between blades of adjacent blade rows of turbomachines discovered more than 40 years ago, about whose existence and consequences there is little awareness today. The turbine test results which led the author in 1957 to hypothesize the existence of the phenomenon of reflecting pressure pulses are described. Subsequently, his 1966 ASME paper is discussed. In it, the author reported on the photographed observations of pressure pulses reflecting between stationary nozzles and moving blades of a water-table turbine at Lehigh University, on the description of the various types of such waves, and on an explanation of some of the resonant blade excitation frequencies observed by National Advisory Committee for Aeronautics (NACA) in a turbine of turbojet engine. This is followed by a description of his 1984 ASME paper, in which more general formulae were derived for the blade excitation frequencies caused by the reflections of pressure pulses between the rotor blades, and both upstream and downstream stator vanes. These equations were subsequently used to explain the blade excitation frequencies measured in an axial compressor stage. Finally, his 1992 AIAA paper is discussed, in which additional formulae relating to the reflecting pressure pulses were derived, and the process of formation of a pressure pulse was explained. To put this work in perspective, the author provided, in mostly chronological order, excerpts from reports on operational problems encountered with turbomachines in service and brief descriptions, from selected publications, of pertinent research work.

Thermodynamic Effect on a Cavitating Inducer—Part I: Geometrical Similarity of Leading Edge Cavities and Cavitation Instabilities

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Jean-Pierre Franc ◽  
Guillaume Boitel ◽  
Michel Riondet ◽  
Éric Janson ◽  
Pierre Ramina ◽  
...  
Keyword(s):  
Transit Time ◽  
Cavity Length ◽  
Cold Water ◽  
Rotation Speed ◽  
Leading Edge ◽  
Cavitation Number ◽  
Thermodynamic Effect ◽  
Cavity Closure ◽  
Cavity Development ◽  
Onset Of Cavitation

The thermodynamic effect on a cavitating inducer is investigated from joint experiments in cold water and Refrigerant 114. The analysis is focused on leading edge cavitation and cavitation instabilities, especially on alternate blade cavitation and supersynchronous rotating cavitation. The cavity length along cylindrical cuts at different radii between the hub and casing is analyzed with respect to the local cavitation number and angle of attack. The similarity in shape of the cavity closure line between water and R114 is examined and deviation caused by thermodynamic effect is clarified. The influence of rotation speed on cavity length is investigated in both fluids and analyzed on the basis of a comparison of characteristic times, namely, the transit time and a thermal time. Thermodynamic delay in the development of leading edge cavities is determined and temperature depressions within the cavities are estimated. Thresholds for the onset of cavitation instabilities are determined for both fluids. The occurrence of cavitation instabilities is discussed with respect to the extent of leading edge cavitation. The thermodynamic delay affecting the occurrence of cavitation instabilities is estimated and compared with the delay on cavity development.

scholarly journals Detection of Onset, Systolic Peak and Dicrotic Notch in Arterial Blood Pressure Pulses

2017 ◽  
Vol 50 (7-8) ◽  
pp. 170-176 ◽  
Author(s):  
Omkar Singh ◽  
Ramesh Kumar Sunkaria
Keyword(s):  
Blood Pressure ◽  
Wavelet Transform ◽  
Arterial Blood Pressure ◽  
Pressure Pulse ◽  
Data Set ◽  
Dicrotic Notch ◽  
Arterial Blood ◽  
Comparison Results ◽  
Empirical Wavelet Transform ◽  
Pressure Pulses

In this paper, we proposed an effective method for detecting fiducial points in arterial blood pressure pulses. An arterial blood pressure pulse normally consists of onset, systolic peak and dicrotic notch. Detection of fiducial points in blood pressure pulses is a critical task and has many potential applications. The proposed method employs empirical wavelet transform for locating the systolic peak and onset of blood pressure pulse. The proposed method first estimates the fundamental frequency of blood pressure pulse using empirical wavelet transform and utilizes the combination of the blood pressure pulse and the estimated frequency for locating onset and systolic peak. For dicrotic notch detection, it utilizes the first-order difference of blood pressure pulse. The algorithm was validated on various open-source databases and was tested on a data set containing 12,230 beats. Two benchmark parameters such as sensitivity and positive predictivity were used for the performance evaluation. The comparison results for accuracy of the detection of systolic peak, onset and dicrotic notch are reported. The proposed method attained a sensitivity and positive predictivity of 99.95% and 99.97%, respectively, for systolic peaks. For onsets, it attained a sensitivity and predictivity of 99.88% and 99.92%, respectively. For dicrotic notches, a sensitivity and positive predictivity of 98.98% and 98.81% were achieved, respectively.

Model of back pressure pulses generated by coupled pressure pulse (CPP) technology

2014 ◽  
Vol 68 ◽  
pp. 175-184 ◽  
Author(s):  
Urs Rhyner ◽  
Robert Mai ◽  
Hans Leibold ◽  
Serge M.A. Biollaz
Keyword(s):  
Pressure Pulse ◽  
Back Pressure ◽  
Pressure Pulses

scholarly journals Dynamic interaction of the cavitating propeller tip vortex with the rudder

2007 ◽  
Vol 14 (4) ◽  
pp. 10-14 ◽  
Author(s):  
Jan Szantyr
Keyword(s):  
High Pressure ◽  
Leading Edge ◽  
Physical Reality ◽  
Dynamic Interaction ◽  
Tip Vortex ◽  
Variable Pressure ◽  
Propeller Design ◽  
Pressure Region ◽  
Pressure Pulses ◽  
Propeller Blades

Dynamic interaction of the cavitating propeller tip vortex with the rudder The hydrodynamic interaction between the ship propeller and the rudder has many aspects. One of the most interesting is the interaction between the cavitating tip vortex shed from the propeller blades and the rudder. This interaction leads to strongly dynamic behaviour of the cavitating vortex, which in turn generates unusually high pressure pulses in its vicinity. Possibly accurate prediction of these pulses is one of the most important problems in the hydrodynamic design of a new ship. The paper presents a relatively simple computational model of the propeller cavitating tip vortex behaviour close to the rudder leading edge. The model is based on the traditional Rankine vortex and on the potential solution of the dynamics of the cylindrical sections of the cavitating kernel passing through the strongly variable pressure field in the vicinity of the rudder leading edge. The model reproduces numerically the experimentally observed process of initial compression of the vortex kernel in the high pressure region near the stagnation point at the rudder leading edge and subsequent explosive growth of the kernel in the low pressure region further downstream. Numerical simulation of this process enables computation of the additional pressure pulses generated due to this phenomenon and transmitted onto the hull surface. This new numerical model of the cavitating tip vortex is incorporated in the modified unsteady lifting surface program for prediction of propeller cavitation, which has been successfully used in the process of propeller design for several years and which recently has been extended to include the effects of propeller — rudder interaction. The results of calculations are compared with the experimental measurements and they demonstrate reasonable agreement between theory and physical reality.

Experimental Measurement of Pressure Pulses From a Pulp Screen Rotor

2010 ◽  
Author(s):  
Sean Delfel ◽  
James Olson ◽  
Carl Ollivier-Gooch ◽  
Phil Wallace
Keyword(s):  
Reynolds Number ◽  
Flow Velocity ◽  
Negative Pressure ◽  
Pressure Pulse ◽  
Pressure Coefficient ◽  
Positive Pressure ◽  
Single Element ◽  
Experimental Measurements ◽  
Main Function ◽  
Pressure Pulses

Pressure screens are the most industrially effective way to remove contaminants from a pulp stream, improving the strength, smoothness, and optical qualities of both new and recycled paper. Pressure screens are comprised of two main components: a screen cylinder with narrow slots or small holes and a rotor. The main function of the rotor is to prevent the narrow cylinder apertures from becoming plugged by pulp and debris. In this study, the pressure pulses generated by a novel multi-element foil (MEF) and a single-element foil rotor in a pressure screen were measured at various foil configurations, rotor speeds, and flow rates. The experimental measurements were compared to the results from a computational fluid dynamics model (CFD). Experimental measurements showed that increasing both the angle-of-attack and the flap angle of the MEF increases the magnitude of the negative pressure pulse and reduce the magnitude of the maximum pressure pulse generated by the rotor. At the optimum configurations, the MEF was shown to produce a 126% higher magnitude negative pressure pulse and a 39% lower magnitude positive pressure pulse. It was also found that at higher tip speeds the magnitude of the pressure pulse varies with tip speed squared and the non-dimensional pressure coefficient is Reynolds number independent. Similarly, at higher tip speeds increasing the velocity of the flow through the slots had no effect on the pressure pulse generated by the rotor. At lower rotor speeds, however, the dimensionless pressure was increasingly depending on Reynolds number as slot flow velocity was increased. This is likely due to the increase in slot flow velocity causing the onset of flow separation over the foil. Finally, the numerical model was shown to accurately predict the pressure pulses generated by the MEF at low angles-of-attack and flap angles. However, the model predicted that the foil would stall at lower angles than what was shown experimentally. This is probably because the CFD model used a solid wall boundary condition rather than modeling the slots in the cylinder, preventing low momentum fluid from re-entering the domain.

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