The Effects of Turbulence Stimulators on Cavitation Inception of Axisymmetric Headforms

1986 ◽  
Vol 108 (2) ◽  
pp. 261-268 ◽  
Author(s):  
T. T. Huang
Keyword(s):  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Repeated Measurements ◽  
Direct Transition ◽  
Patch Type ◽  
Mean Values ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Small Band ◽  
Made In

Cavitation inception observations were made in the DTNSRDC 36-inch water tunnel on three axisymmetric headforms with and without various turbulence stimulators installed. Direct transition measurements, made on two of the headforms with and without distributed surface roughness, were found to correlate reasonably well with the computed spatial amplification factors, eN, at the separation locations. The computed eN factors were then used to estimate transition at other test conditions (without direct transition measurements). The predicted transition locations on all three smooth headforms occur at positions considerably aft of the minimum pressure locations. The three smooth headforms have different types of incipient cavitation—small band, transient spot, traveling bubble, and attached spot. The measured cavitation inception numbers for those cases are all significantly smaller than the computed negative values of the minimum pressure coefficient, −Cpmin. The predicted transition locations on the three headforms with densely and loosely packed 60-μm distributed roughness occur at a considerable distance upstream of the minimum pressure locations. Therefore, the flows over all three headforms with distributed roughness are turbulent at the Cpmin locations for the Reynolds numbers tested. Under this condition, the measured cavitation inception numbers are found to approximate well with the values of −Cpmin. The incipient cavitation is in the form of attached small bubble lines evenly distributed around the minimum pressure locations. The measured cavitation inception numbers for the three headforms with an isolated roughness band located upstream of the minimum pressure locations are found to approximate the computed values of −Cpmin when the roughness Reynolds number (Rk = ukK/ν) is equal to 600 and to be smaller than the values of −Cpmin when the value of Rk is less than 600. The incipient cavitation observed is attached patch type cavitation occurring in the vicinity of the minimum pressure location. The uncertainty of the measured cavitation inception numbers, in terms of the maximum deviations form the mean values of repeated measurements, is generally less than 0.02.

Cavitation Inception Observations on Axisymmetric Bodies at Supercritical Reynolds Numbers

1976 ◽  
Vol 20 (01) ◽  
pp. 40-50
Author(s):  
V. H. Arakeri ◽  
A. J. Acosta
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
The Body ◽  
Laminar Separation ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Pressure Point ◽  
A Site ◽  
Axisymmetric Bodies

A laminar separation on a body provides a site for the inception of cavitation. The separated region disappears when the boundary layer upstream becomes turbulent; this may occur naturally or by stimulation. The consequences of this disappearance on the values of the cavitation inception index and the type and appearance of the cavitation at inception are investigated on three different axisymmetric bodies. On one of these bodies, a hemisphere-cylinder, a trip near the nose so energized the boundary layer that it was impossible for any form of cavitation to remain attached to the body even when a tension of about one half atm. existed at the minimum pressure point on the body.

An Experimental Investigation of Cavitation Inception and Development on a Two-Dimensional Eppler Hydrofoil

1999 ◽  
Vol 122 (1) ◽  
pp. 164-173 ◽  
Author(s):  
J.-A. Astolfi ◽  
P. Dorange ◽  
J.-Y. Billard ◽  
I. Cid Tomas
Keyword(s):  
Reverse Flow ◽  
Pressure Coefficient ◽  
Large Angle ◽  
Separated Flow ◽  
Leading Edge ◽  
Angle Of Incidence ◽  
Two Dimensional ◽  
Velocity Measurements ◽  
Cavitation Inception ◽  
Minimum Pressure

Cavitation inception and development on a two-dimensional foil with an Eppler E817 cross section issued from an inverse calculus have been experimentally investigated. The foil is theoretically designed to have a wide cavitation-free bucket allowing a large range of cavitation-free angle of incidence (Eppler, R., 1990, Airfoil Design and Data, Springer-Verlag, Berlin). The inception cavitation numbers, the noise level, the velocity distribution, the minimum pressure coefficient, the cavitation patterns (bubble, leading edge “band type” cavitation, attached sheet cavity), together with the sheet cavity length have been experimentally determined. Effects on the velocity field have been studied too with a slightly developed cavitation. For angles of incidence larger than 1 deg, a great difference exists between the inception cavitation number and the theoretical minimum pressure coefficient. However it is in agreement with the measured one obtained from velocity measurements (for 0 deg<α<6 deg). Discrepancy between theory and experiment on scale models is generally attributed to a flow separation at the leading edge. Although there are some indications of a separated flow at the leading edge, the velocity measurements do not show reverse flow with clearly detected negative velocities excepted for a large angle of incidence equal to 10 deg. Concerning sheet cavity development, the length cavity is found to scale as [σ/2α−αiσ]−m with m close to 2, for length cavities that do not exceed half the foil chord and for σ/2α−αiσ larger than about 30. [S0098-2202(00)00201-7]

Viscous and Nuclei Effects on Hydrodynamic Loadings and Cavitation of a NACA 66 (MOD) Foil Section

1989 ◽  
Vol 111 (3) ◽  
pp. 306-316 ◽  
Author(s):  
Y. T. Shen ◽  
P. E. Dimotakis
Keyword(s):  
Pressure Distribution ◽  
Pressure Coefficient ◽  
Leading Edge ◽  
Full Scale ◽  
Pressure Loading ◽  
Foil Surface ◽  
Negative Minimum ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Bubble Cavitation

A series of experiments has been conducted on a two-dimensional NACA 66 (MOD) foil to examine the effects of viscosity and nuclei on cavitation inception. In this paper the main discussions center on two foil angles having different types of pressure loadings to represent a propeller blade section operating at design and off-design conditions. At one degree design angle of attack the foil experiences a rooftop-type gradually varying pressure distribution. At three degrees off-design angle of attack the foil experiences a sharp suction pressure peak near the leading edge. Cebeci’s viscid/inviscid interactive code is used to compute the viscous scale effects on the development of the boundary layer, lift, drag and pressure distribution on the foil. Chahine’s multibubble interaction code is used to compute the effect of nuclei, test speeds, foil size and foil surface on traveling bubble cavitation. Both computer codes are found to agree satisfactorily with the experimental measurements reported here. Two assumptions commonly used to predict full scale surface cavitation from model tests are examined experimentally and theoretically. The first assumption states that cavitation inception occurs when the static pressure reaches the vapor pressure. On the contrary, the experiments showed that the water flowing over the foil surface sustained significant amounts of tension during inception of midchord bubble cavitation as well as leading edge sheet cavitation. The second assumption states that there is no scale effect on the values of negative minimum pressure coefficient. In the case of a rooftop-type pressure loading, the second assumption is supported by the pressure numerical calculations. However, in the case of a pressure loading with a strong suction peak near the leading edge the value of negative minimum pressure coefficient is as much as 12 to 15 percent lower on a model than at full scale.

Viscous Effects in the Inception of Cavitation

1981 ◽  
Vol 103 (2) ◽  
pp. 280-287 ◽  
Author(s):  
V. H. Arakeri ◽  
Allan Acosta
Keyword(s):  
Fluid Flow ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Viscous Effects ◽  
Laminar Separation ◽  
Wake Flows ◽  
Cavitation Inception ◽  
High Reynolds Numbers ◽  
Real Fluid ◽  
High Reynolds

The inception of cavitation in the steady flow of liquids around bodies is seen to depend upon the real fluid flow around the bodies as well as the supply of nucleating cavitation sources—or nuclei—within the fluid. A primary distinction is made between bodies having a laminar separation or not having a laminar separation. The former group is relatively insensitive to the nuclei concentration whereas the latter is much more sensitive. Except for the case of fully separated wake flows and for gaseous cavitation by diffusion the cavitation inception index tends always to be less than the magnitude of the minimum pressure coefficient and only approaches that value for high Reynolds numbers in flows well supplied with nuclei.

scholarly journals Interfacial integrity of bonded restorations with self-etching adhesives: Water storage and thermo-mechanical cycling

2012 ◽  
Vol 06 (02) ◽  
pp. 169-177
Author(s):  
Gislaine Cristine Martins ◽  
Alfonso Sánchez-Ayala ◽  
Paulo Henrique Perlatti D’Alpino ◽  
Abraham Lincoln Calixto ◽  
João Carlos Gomes ◽  
...  
Keyword(s):  
Bond Strength ◽  
Water Storage ◽  
Single Bond ◽  
Third Molars ◽  
Class V ◽  
Mean Values ◽  
Composite Restorations ◽  
Mechanical Cycling ◽  
Interfacial Gap ◽  
Made In

ABSTRACTObjectives: Objective: To evaluate the effect of thermo-mechanical cycling (TMC) on the microleakage (μL) and axial gap width (AG) of Class V bonded restorations in premolars using self-etching adhesive systems. The bond strength of composite restorations to dentin (μTBS) using the same adhesives was also evaluated in third molars after water storage: 24 h and 6 months. The research hypotheses were tested for the results of two self-etching adhesives in comparison when a conventional two-step adhesive was used: (1) the μL and AG would be lower, regardless of TMC; (2) the μTBS of self-etching adhesives would be higher, irrespective of evaluation times.Methods: Sixty Class V composite restorations were made in 30 premolars and bonded with Adper Single Bond 2 (ASB2), AdheSE (ASE), and Adper Prompt L-Pop (APL-P) (n=20). Dentin μL and AG were immediately measured for half of the sample. The other half was evaluated after TMC. Eighteen third molars were also selected and bonded using the same adhesives to test the μTBS to dentin. Specimens were evaluated after 24 h and 6 months of water storage.Results: No differences in μL and AG were found among the groups (P>.05). The μTBS mean values were: ASB2>ASE>APL-P (P<.05); only Adper Single Bond 2 presented a significantly lower μTBS after water storage (P<.05)Conclusions: The bonding approach does not influence the microleakage and interfacial gap extension. Despite the decrease in the mean values, the bond strength to dentin of the conventional, two-step adhesive remains high after 6 months of water storage. (Eur J Dent 2012;6:169-177)

Collapse of Arteries Subjected to an External Band of Pressure

1980 ◽  
Vol 102 (1) ◽  
pp. 8-22 ◽  
Author(s):  
A. M. Hecht ◽  
H. Yeh ◽  
S. M. K. Chung
Keyword(s):  
Reynolds Number ◽  
Blood Flow ◽  
Cylindrical Shell ◽  
Orthotropic Cylindrical Shell ◽  
Reynolds Numbers ◽  
Intraluminal Pressure ◽  
Collapse Pressure ◽  
Vessel Size ◽  
Flow Reynolds Number ◽  
Small Band

Collapse of arteries subjected to a band of hydrostatic pressure of finite length is analyzed. The vessel is treated as a long, thin, linearly elastic, orthotropic cylindrical shell, homogeneous in composition, and with negligible radial stresses. Blood in the vessel is treated as a Newtonian fluid and the Reynolds number is of order 1. Results are obtained for effects of the following factors on arterial collapse: intraluminal pressure, length of the pressure band, elastic properties of the vessel, initial stress both longitudinally and circumferentially, blood flow Reynolds number, compressibility, and wall thickness to radius ratio. It is found that the predominant parameter influencing vessel collapse for the intermediate range of vessel size and blood flow Reynolds numbers studied is the preconstricted intraluminal pressure. For pressure bands less than about 10 vessel radii the collapse pressure increases sharply with increasing intraluminal pressure. Initial axial prestress is found to be highly stabilizing for small band lengths. The effects of fluid flow are found to be small for pressure bands of less than 100 vessel radii. No dramatic orthotropic vessel behavior is apparent. The analysis shows that any reduction in intraluminal pressure, such as that produced by an upstream obstruction, will significantly lower the required collapse pressure. Medical implications of this analysis to Legg-Perthes disease are discussed.

O26 QUALITY OF LIFE FOR ACHALASIA PATIENTS IS THE SAME AFTER PER-ORAL ENDOSCOPIC MYOTOMY (POEM) AND HELLER MYOTOMY

2019 ◽  
Vol 32 (Supplement_2) ◽  
Author(s):  
Vrakopoulou Gavriella Zoi ◽  
Di Maggio Francesco ◽  
Barbieri Lavinia ◽  
Zeki Sebastian ◽  
Dunn Jason M ◽  
...  
Keyword(s):  
Repeated Measurements ◽  
Similar Degree ◽  
Complication Rates ◽  
Mean Values ◽  
Per Oral Endoscopic Myotomy ◽  
Eckardt Score ◽  
Significant Difference ◽  
Endoscopic Myotomy ◽  
Per Oral

Abstract Aim This study aimed to compare the efficacy and safety of LHM and POEM for esophageal achalasia. Background & Methods Laparoscopic Heller’s myotomy (LHM) has been the gold standard of treatment, however per-oral endoscopic myotomy (POEM) was recently established as a treatment option for achalasia. A prospective review was performed for all patients submitted to LHM or POEM in our institution from 10/2012 to 06/2018, and have completed a minimum follow up period of 6 months. The diagnostic work-up included gastroscopy, barium study and high-resolution manometry (HRM). All patients underwent a clinical evaluation 6 weeks after treatment and a surveillance gastroscopy in the 1st postoperative year. HRM and pH studies were offered to all patients after 6 months. Standardized questionnaires evaluating Eckardt, GERD and achalasia QoL (Urbach) scores were completed pre- and postoperatively. Statistical analyses were performed with SPSS version 23.0. Repeated measurements analysis of variance was used to compare changes in mean values during follow up and between the two types of surgery. P values < 0.05 were considered significant. Results Eighty patients (34 women and 46 men) with mean age 42.6 years (16.2) underwent POEM (n=39) or LHM (n=41). QoL score was significantly improved in both study groups (p<0.001) with a similar degree of improvement (p=0.486). Eckardt scores showed a significant improvement in both groups, but repeated measurements analysis revealed a significant effect with time (p=0.038) with a greater improvement in POEM group. Moreover, Eckardt score change was similar between LHM and POEM patients without prior treatments (p=0.724), but in those with prior treatments the improvement trended higher in POEM group (p=0.087). GERD score had a similar and significant decrease in both groups (p=0.439), but in those with prior treatments the improvement was greater in LHM group (p=0.018). There was no significant difference regarding the complication rates for both groups (Clavien-Dindo I-IIIa). Conclusions POEM compares favorably with LHM as treatment for achalasia, as statistically significant improvement in QoL, GERD and Eckardt scores was recorded in both groups. In patients with prior treatments, POEM tends to achieve a greater improvement of Eckardt score and LHM a greater reduction regarding GERD score.

Hydrographic and nutrient chemistry surveys in the western English channel during 1963 and 1964

1972 ◽  
Vol 52 (4) ◽  
pp. 915-930 ◽  
Author(s):  
F. A. J. Armstrong ◽  
E. I. Butler ◽  
G. T. Boalch
Keyword(s):  
Suspended Matter ◽  
Low Temperatures ◽  
English Channel ◽  
Nitrogen And Phosphorus ◽  
Mean Values ◽  
Average Temperature ◽  
Significant Difference ◽  
Nutrient Chemistry ◽  
Phosphate Silicate ◽  
Made In

Three surveys were made in 1963 and five in 1964 in the area of the English Channel between the English and French coasts and between 3° 40' W and 5°10' W. This area had been surveyed in 1961 and 1962. Temperature and salinity were determined at o, to and 50 m and phosphate silicate and nitrate at 10 and 50 m. The results are presented graphically. Temperature and salinity were compared with Lumby's 25–year averages. The year 1963 started with unusually low temperatures and salinities higher than average. Temperature remained low in the spring, but salinity decreased. The year 1964 started with temperatures and salinities above normal, but during the rest of the year values were close to average. Nitrate in January 1964 was higher than in January 1963. Analyses of suspended matter at 12m were made for carbon, nitrogen and phosphorus on most surveys, and mean values for the whole area are given. Suspended carbon was 67 /ig C/l. in January 1963 and 51 /*g C/l. in January 1964, a significant difference. Increases in sus-pended carbon, nitrogen and phosphorus were found in spring and summer 1964.

scholarly journals Design and Testing of a LUT Airfoil for Straight-Bladed Vertical Axis Wind Turbines

2018 ◽  
Vol 8 (11) ◽  
pp. 2266 ◽  
Author(s):  
Shoutu Li ◽  
Ye Li ◽  
Congxin Yang ◽  
Xuyao Zhang ◽  
Qing Wang ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Optimization Method ◽  
Geometrical Parameters ◽  
Vertical Axis Wind Turbines ◽  
University Of Technology ◽  
Horizontal Axis Wind Turbines

The airfoil plays an important role in improving the performance of wind turbines. However, there is less research dedicated to the airfoils for Vertical Axis Wind Turbines (VAWTs) compared to the research on Horizontal Axis Wind Turbines (HAWTs). With the objective of maximizing the aerodynamic performance of the airfoil by optimizing its geometrical parameters and by considering the law of motion of VAWTs, a new airfoil, designated the LUT airfoil (Lanzhou University of Technology), was designed for lift-driven VAWTs by employing the sequential quadratic programming optimization method. Afterwards, the pressure on the surface of the airfoil and the flow velocity were measured in steady conditions by employing wind tunnel experiments and particle image velocimetry technology. Then, the distribution of the pressure coefficient and aerodynamic loads were analyzed for the LUT airfoil under free transition. The results show that the LUT airfoil has a moderate thickness (20.77%) and moderate camber (1.11%). Moreover, compared to the airfoils commonly used for VAWTs, the LUT airfoil, with a wide drag bucket and gentle stall performance, achieves a higher maximum lift coefficient and lift–drag ratios at the Reynolds numbers 3 × 105 and 5 × 105.

scholarly journals A Study of Drag Reduction on Cylinders with Different V-Groove Depths on the Surface

Water ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 36
Author(s):  
Jiyang Qi ◽  
Yue Qi ◽  
Qunyan Chen ◽  
Fei Yan
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Vortex Structure ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Groove Surface ◽  
Smooth Cylinder ◽  
Groove Structure ◽  
Reduction Effect

In this study, the drag reduction effect is studied for a cylinder with different V-groove depths on its surface using a k-ω/SST (Shear Stress Transport) turbulence model of computational fluid dynamics (CFD), while a particle image velocimetry (PIV) system is employed to analyze the wake characteristics for a smooth cylinder and a cylinder with different V-groove depths on its surface at different Reynolds numbers. The study focuses on the characteristics of the different V-groove depths on lift coefficient, drag coefficient, the velocity distribution of flow field, pressure coefficient, vortex shedding, and vortex structure. In comparison with a smooth cylinder, the lift coefficient and drag coefficient can be reduced for a cylinder with different V-groove depths on its surface, and the maximum reduction rates of lift coefficient and drag coefficient are about 34.4% and 16%, respectively. Otherwise, the vortex structure presents a complete symmetry for the smooth cylinder, however, the symmetry of the vortex structure becomes insignificant for the V-shaped groove structure with different depths. This is also an important reason for the drag reduction effect of a cylinder with a V-groove surface.

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