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.

Numerical Analysis of High-Speed Bodies in Partially Cavitating Axisymmetric Flow

2005 ◽  
Vol 127 (1) ◽  
pp. 41-54 ◽  
Author(s):  
Abraham N. Varghese ◽  
James S. Uhlman ◽  
Ivan N. Kirschner
Keyword(s):  
High Speed ◽  
Cone Angle ◽  
Axisymmetric Flow ◽  
Cylindrical Body ◽  
Partial Cavitation ◽  
Conical Section ◽  
Cavity Closure ◽  
Disk Cavitator ◽  
Element Technique ◽  
Axisymmetric Bodies

Partial cavitation of high-speed axisymmetric bodies is modeled using a steady potential-flow boundary-element technique. The effects of several key parameters defining the vehicle geometry are examined for configurations consisting of a disk cavitator followed by a conical section and ending in a cylindrical body. A single cavity is assumed to detach at the edge of the disk. A variety of conditions have been studied, including cavity closure on either the conical or cylindrical portions of the vehicle, variations in the cone angle, and variations in the radius of the cylindrical section. The results for the partially cavitating case are also compared with those for the supercavitating case.

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.

High-Performance Partially Cavitating Hydrofoils

2007 ◽  
Vol 51 (04) ◽  
pp. 313-325
Author(s):  
Jim E. Kopriva ◽  
Eduard L. Amromin ◽  
Roger E. A. Arndt ◽  
Martin Wosnik ◽  
Svetlana Kovinskaya
Keyword(s):  
High Performance ◽  
Cross Flow ◽  
Local Pressure ◽  
Design Algorithm ◽  
Partial Cavitation ◽  
Fluid Theory ◽  
Cavity Closure ◽  
Wetted Area ◽  
Naca 0015 ◽  
Cavitating Hydrofoil

Partial cavitation reduces hydrofoil wetted area and friction, but usually with a significant drag penalty associated with unsteady cavity dynamics. A design concept for a high-performance partially cavitating hydrofoil that centers on the suppression of these oscillations by tuning the local pressure gradient in the region of cavity closure is described. The design algorithm is based on ideal fluid theory. An example of this design is the OK-2003 hydrofoil, which is derived from the NACA-0015 geometry. The concept is verified through water tunnel experiments. It is found that under partial cavitation, a two-dimensional hydrofoil exhibits up to a 100% increase in the lift-to-drag ratio compared to its noncavitating conditions. The substantial increase in this ratio relative to the ratio exhibited by the initial NACA-0015 hydrofoil remains significant within a 3 deg range of angle of attack and under a variation of cavitation number of about ±0.2. It was also found that this new hydrofoil design reduces hydrodynamic force pulsations under partially cavitating conditions to operational levels typical of noncavitating flow. In order to further verify the design benefits, the effects of cross flow have been studied with a swept hydrofoil of the same cross section. It was found that outstanding performance of the designed cavitating hydrofoil is retained with 15 deg sweep.

An Experimental Study of Unsteady Partial Cavitation

2004 ◽  
Vol 126 (1) ◽  
pp. 94-101 ◽  
Author(s):  
Jean-Baptiste Leroux ◽  
Jacques Andre´ Astolfi ◽  
Jean Yves Billard
Keyword(s):  
Cavity Length ◽  
Pressure Fluctuations ◽  
Cavity Growth ◽  
Pressure Measurements ◽  
Cloud Cavitation ◽  
Hydraulic Machinery ◽  
Partial Cavitation ◽  
Basic Physics ◽  
Vapor Cloud ◽  
Cavity Closure

Unsteady partial cavitation can cause damage to hydraulic machinery and understanding it requires knowledge of the basic physics involved. This paper presents the main results of a research program based on wall-pressure measurements aimed at studying unsteadiness in partial cavitation. Several features have been pointed out. For cavity lengths that did not exceed half the foil chord the cavity was stated to be stable. At the cavity closure a peak of pressure fluctuations was recorded originating from local cavity unsteadiness in the closure region at a frequency depending on the cavity length. Conversely, cavities larger than half the foil chord were stated to be unstable. They were characterized by a cavity growth/destabilization cycle settled at a frequency lower than the previous ones. During cavity growth, the closure region fluctuated more and pressure fluctuations traveling in the cavity wake were detected. When the cavity was half the foil chord, cavity growth was slowed down and counterbalanced by large vapor cloud shedding. When the cavity length was maximum (l/c∼0.7–0.8), it was strongly destabilized. The reason for such destabilization is discussed at the end of the paper. It is widely believed that the cavity instability originates from a process involving the shedding of vapor clouds during cavity growth, a re-entrant jet, and a shock wave phenomenon due to the collapse of a large cloud cavitation.

Numerical Simulation of Natural Cavitating Flow over Axisymmetric Bodies

2012 ◽  
Vol 226-228 ◽  
pp. 825-830
Author(s):  
Qian Kun Liu ◽  
Ye Gao
Keyword(s):  
Numerical Simulation ◽  
Quantitative Agreement ◽  
Hydrodynamic Characteristics ◽  
Cavitating Flows ◽  
Cavitation Region ◽  
Cavity Closure ◽  
Disk Cavitator ◽  
Cfd Method ◽  
Analytical Relations ◽  
Axisymmetric Bodies

The hydrodynamic characteristics of bodies are greatly affected by cavitation. Coupling with natural cavitaion model, a multiphase CFD method is developed and is employed to simulate supercavitating and partial cavitating flows over axisymmetric bodies using FLUENT 6.2. The results of supercavitation of a disk cavitator agree well with the boundary element method (BEM), the analytical relations and available experimental results. The present computations and the BEM results are compared with experiments for partial cavitating flows over three typical axisymmetric bodies and the results are discussed. Limitations are on the pressure prediction in the cavity closure region for the BEM, although fairly good quantitative agreement is obtained for three axisymmetric bodies at most of cavitation region. The present computational model on cavitating flows are validated, offering references and bases for hydrodynamic researches.

Study of the flow in a cryogenic pump under different cavitation inducements by considering the thermodynamic effect

2019 ◽  
Vol 30 (9) ◽  
pp. 4307-4329 ◽  
Author(s):  
Chunlei Shao ◽  
Zhongyuan Zhang ◽  
Jianfeng Zhou
Keyword(s):  
Surface Roughness ◽  
Flow Rate ◽  
Volume Fraction ◽  
Inlet Pressure ◽  
Hydraulic Loss ◽  
Cavitation Model ◽  
Content Type ◽  
Cavitation Performance ◽  
Cryogenic Pump ◽  
Thermodynamic Effect

Purpose The purpose of this paper is to accurately predict the cavitation performance of a cryogenic pump and reveal the influence of the inlet pressure, the surface roughness and the flow rate on the cavitation performance. Design/methodology/approach Firstly, the Zwart cavitation model was modified by considering the thermodynamic effect. Secondly, the feasibility of the modified model was validated by the cavitation test of a hydrofoil. Thirdly, the effects of the inlet pressure, the surface roughness and the flow rate on cavitation flow in the cryogenic pump were studied by using the modified cavitation model. Findings The modified cavitation model can predict the cavitation performance of the cryogenic pump more accurately than the Zwart cavitation model. The thermodynamic effect inhibits cavitation development to a certain extent. The higher the vapor volume fraction, the lower the pressure and the lower the temperature. At the initial stage of the cavitation, the head increases first and then decreases with the increase of the roughness. When the cavitation develops to a certain degree, the head decreases with the increase of the roughness. With the decrease of the flow rate, the hydraulic loss increases and the cavitation at the impeller intensifies. Originality/value A cavitation model considering the thermodynamic effect is proposed. The mechanism of the influence of the roughness on the performance of the cryogenic pump is revealed from two aspects. Taking the hydraulic loss as a bridge, the relationships among flow rates, vapor volume fractions, streamlines, temperatures and pressures are established.

Reliability of the Minimum Masking Level as Outcome Variable in Tinnitus Clinical Research

2020 ◽  
Vol 29 (3) ◽  
pp. 429-435
Author(s):  
Patricia C. Mancini ◽  
Richard S. Tyler ◽  
Hyung Jin Jun ◽  
Tang-Chuan Wang ◽  
Helena Ji ◽  
...  
Keyword(s):  
Standard Deviation ◽  
High Frequency ◽  
Pearson Correlation ◽  
Correlation Coefficients ◽  
Outcome Variable ◽  
Reliable Estimate ◽  
Moderate Correlation ◽  
Trained Subjects ◽  
The Relationship ◽  
Minimum Intensity

Purpose The minimum masking level (MML) is the minimum intensity of a stimulus required to just totally mask the tinnitus. Treatments aimed at reducing the tinnitus itself should attempt to measure the magnitude of the tinnitus. The objective of this study was to evaluate the reliability of the MML. Method Sample consisted of 59 tinnitus patients who reported stable tinnitus. We obtained MML measures on two visits, separated by about 2–3 weeks. We used two noise types: speech-shaped noise and high-frequency emphasis noise. We also investigated the relationship between the MML and tinnitus loudness estimates and the Tinnitus Handicap Questionnaire (THQ). Results There were differences across the different noise types. The within-session standard deviation averaged across subjects varied between 1.3 and 1.8 dB. Across the two sessions, the Pearson correlation coefficients, range was r = .84. There was a weak relationship between the dB SL MML and loudness, and between the MML and the THQ. A moderate correlation ( r = .44) was found between the THQ and loudness estimates. Conclusions We conclude that the dB SL MML can be a reliable estimate of tinnitus magnitude, with expected standard deviations in trained subjects of about 1.5 dB. It appears that the dB SL MML and loudness estimates are not closely related.

Clausal Density Between Ages 4 and 9 Years for the Edmonton Narrative Norms Instrument: Reference Data and Psychometric Properties

2020 ◽  
pp. 1-15
Author(s):  
Ling-Yu Guo ◽  
Phyllis Schneider ◽  
William Harrison
Keyword(s):  
Diagnostic Accuracy ◽  
Psychometric Properties ◽  
Language Impairment ◽  
Reference Data ◽  
Reliability And Validity ◽  
Correlation Coefficients ◽  
Criterion Validity ◽  
Likelihood Ratios ◽  
Generation Task ◽  
Sensitivity Specificity

Purpose This study provided reference data and examined psychometric properties for clausal density (CD; i.e., number of clauses per utterance) in children between ages 4 and 9 years from the database of the Edmonton Narrative Norms Instrument (ENNI). Method Participants in the ENNI database included 300 children with typical language (TL) and 77 children with language impairment (LI) between the ages of 4;0 (years;months) and 9;11. Narrative samples were collected using a story generation task, in which children were asked to tell stories based on six picture sequences. CD was computed from the narrative samples. The split-half reliability, concurrent criterion validity, and diagnostic accuracy were evaluated for CD by age. Results CD scores increased significantly between ages 4 and 9 years in children with TL and those with LI. Children with TL produced higher CD scores than those with LI at each age level. In addition, the correlation coefficients for the split-half reliability and concurrent criterion validity of CD scores were all significant at each age level, with the magnitude ranging from small to large. The diagnostic accuracy of CD scores, as revealed by sensitivity, specificity, and likelihood ratios, was poor. Conclusions The finding on diagnostic accuracy did not support the use of CD for identifying children with LI between ages 4 and 9 years. However, given the attested reliability and validity for CD, reference data of CD from the ENNI database can be used for evaluating children's difficulties with complex syntax and monitoring their change over time. Supplemental Material https://doi.org/10.23641/asha.13172129

Interobserver Reliability Using the Phonetic Level Evaluation With Severely and Profoundly Hearing-Impaired Children

1991 ◽  
Vol 34 (5) ◽  
pp. 989-999 ◽  
Author(s):  
Stephanie Shaw ◽  
Truman E. Coggins
Keyword(s):  
Interrater Reliability ◽  
Interobserver Reliability ◽  
Intraclass Correlation ◽  
Correlation Coefficients ◽  
Hearing Impaired ◽  
Intraclass Correlation Coefficients ◽  
Assessment Measure ◽  
Impaired Children ◽  
Speech Assessment ◽  
Hearing Impaired Children

This study examines whether observers reliably categorize selected speech production behaviors in hearing-impaired children. A group of experienced speech-language pathologists was trained to score the elicited imitations of 5 profoundly and 5 severely hearing-impaired subjects using the Phonetic Level Evaluation (Ling, 1976). Interrater reliability was calculated using intraclass correlation coefficients. Overall, the magnitude of the coefficients was found to be considerably below what would be accepted in published behavioral research. Failure to obtain acceptably high levels of reliability suggests that the Phonetic Level Evaluation may not yet be an accurate and objective speech assessment measure for hearing-impaired children.

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