Numerical Analysis of Cavitation Inception and Desinence Behind Orifices

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
E. L. Amromin
Keyword(s):  
Experimental Data ◽  
Numerical Analysis ◽  
Separated Flow ◽  
Computational Procedure ◽  
Cavitation Number ◽  
Laminar Flows ◽  
Cavity Pressure ◽  
Cavitation Inception ◽  
Separation Zones

Abstract Experimental results and trends for cavitation inception and desinence behind orifices in microchannels are quite different from the data obtained during previous experiments in much larger facilities. The objective of this paper is to explain these differences via a numerical analysis. The employed computational procedure is divided into two parts. The first part is computation of an axisymmetric separated flow around the orifice. The second part is determination of characteristics of cavities appearing within separation zones. The provided analysis of the experimental data of other researchers pointed out two sources of the above-mentioned differences. First, for larger orifices, the cavities appear in the cores of drifting vortices. For such a situation, cavitation inception and desinence number increases with the inflow speed due to an impact of turbulence, but there is no such an increase for microbubbles with laminar flows. Second, because of the difficulty to measure the cavity pressure in microbubbles, cavitation number is usually defined with employment of the vapor pressure, and this leads to misinterpretation of the measurements and their trends.

Computation of Cavitation Inception Number for Surface Irregularities

2003 ◽  
Author(s):  
Eduard Amromin
Keyword(s):  
Reynolds Equation ◽  
Numerical Technique ◽  
Theoretical Concept ◽  
Base Pressure ◽  
Wind Tunnels ◽  
Cavitation Inception ◽  
Surface Irregularities ◽  
Viscous Core ◽  
Separation Zones

Computation of cavitation inception number for isolated surface irregularities is performed with the assumption that cavitation bubbles appear in vortices located within viscous separation zones behind these irregularities. The numerical analysis consists of four parts. The first part is determination of the base pressure within separation zone and irregularity drag by using viscous-inviscid interaction concept for an obstacle in non-uniform incoming flow. This part is validated by the well-known experimental data for cavitation-free flows behind backward-facing steps and within specially designed wind tunnels (by Tani et al {1] and Agarwal & Simpson [2]). The second part is determination of vortex intensity by using the base pressure and drag in an empirical formula. The third part is determination of vortex viscous core from an asymptotic solution of Reynolds equation for the vicinity of a vortex in the turbulent flow. The fourth part is calculation of cavitation inception number for a bubble with taking into account the surface tension effect. The suggested theoretical concept and numerical technique are validated by comparison with measurements for irregularities over flat walls and 2D hydrofoils (by Arndt et al [3] and Holl et al [4]).

Impact of Hydrofoil Material on Cavitation Inception and Desinence

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Eduard Amromin
Keyword(s):  
Experimental Data ◽  
Numerical Analysis ◽  
Fluid Structure Interaction ◽  
Pressure Pulsations ◽  
Flow Induced Vibration ◽  
Fluid Structure ◽  
Cavitation Inception ◽  
Structure Interaction

Flow-induced vibration of hydrofoils affects pressure pulsations on their surfaces and influences cavitation inception and desinence. As these pulsations depend on the hydrofoil material, cavitation inception and desinence numbers for hydrofoils of the same shape made from different metals can be substantially different. This conclusion is based on the comparison of the multistep numerical analysis of fluid–structure interaction for hydrofoils Cav2003 with earlier obtained experimental data for them. The material impact on cavitation must be taken into account in future experiments.

Equilibrium Sorptions in Heterogeneous Ion Exchange Membranes

1992 ◽  
Vol 57 (9) ◽  
pp. 1905-1914
Author(s):  
Miroslav Bleha ◽  
Věra Šumberová
Keyword(s):  
Experimental Data ◽  
Ion Exchange ◽  
Total Content ◽  
Distribution Coefficients ◽  
Exchange Capacity ◽  
Ion Exchange Membranes ◽  
Ion Exchange Capacity ◽  
Equilibrium Sorption ◽  
Inhomogeneity Factor

The equilibrium sorption of uni-univalent electrolytes (NaCl, KCl) in heterogeneous cation exchange membranes with various contents of the ion exchange component and in ion exchange membranes Ralex was investigated. Using experimental data which express the concentration dependence of equilibrium sorption, validity of the Donnan relation for the systems under investigation was tested and values of the Glueckauf inhomogeneity factor for Ralex membranes were determined. Determination of the equilibrium sorption allows the effect of the total content of internal water and of the ion-exchange capacity on the distribution coefficients of the electrolyte to be determined.

Numerical evaluation of hydrodynamic characteristics of planing hulls by using a hybrid method

2021 ◽  
pp. 147509022199024
Author(s):  
Emre Kahramanoglu ◽  
Silvia Pennino ◽  
Huseyin Yilmaz
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Design Stage ◽  
Hydrodynamic Characteristics ◽  
Calm Water ◽  
Preliminary Design Stage ◽  
Reduction Function ◽  
Hull Forms ◽  
Good Agreement

The hydrodynamic characteristics of the planing hulls in particular at the planing regime are completely different from the conventional hull forms and the determination of these characteristics is more complicated. In the present study, calm water hydrodynamic characteristics of planing hulls are investigated using a hybrid method. The hybrid method combines the dynamic trim and sinkage from the Zarnick approach with the Savitsky method in order to calculate the total resistance of the planing hull. Since the obtained dynamic trim and sinkage values by using the original Zarnick approach are not in good agreement with experimental data, an improvement is applied to the hybrid method using a reduction function proposed by Garme. The numerical results obtained by the hybrid and improved hybrid method are compared with each other and available experimental data. The results indicate that the improved hybrid method gives better results compared to the hybrid method, especially for the dynamic trim and resistance. Although the results have some discrepancies with experimental data in terms of resistance, trim and sinkage, the improved hybrid method becomes appealing particularly for the preliminary design stage of the planing hulls.

scholarly journals Identification of coexisting dynamics in boundary layer flows through proper orthogonal decomposition with weighting matrices

Meccanica ◽  
2021 ◽  
Author(s):  
Matteo Dellacasagrande ◽  
Dario Barsi ◽  
Patrizia Bagnerini ◽  
Davide Lengani ◽  
Daniele Simoni
Keyword(s):  
Experimental Data ◽  
Proper Orthogonal Decomposition ◽  
Fourier Transforms ◽  
Free Stream ◽  
Numerical Test ◽  
Separated Flow ◽  
Orthogonal Decomposition ◽  
Inner Product ◽  
Test Case ◽  
Proper Orthogonal

AbstractA different version of the classic proper orthogonal decomposition (POD) procedure introducing spatial and temporal weighting matrices is proposed. Furthermore, a newly defined non-Euclidean (NE) inner product that retain similarities with the POD is introduced in the paper. The aim is to emphasize fluctuation events localized in spatio-temporal regions with low kinetic energy magnitude, which are not highlighted by the classic POD. The different variants proposed in this work are applied to numerical and experimental data, highlighting analogies and differences with respect to the classic and other normalized variants of POD available in the literature. The numerical test case provides a noise-free environment of the strongly organized vortex shedding behind a cylinder. Conversely, experimental data describing transitional boundary layers are used to test the capability of the procedures in strongly not uniform flows. By-pass and separated flow transition processes developing with high free-stream disturbances have been considered. In both cases streaky structures are expected to interact with other vortical structures (i.e. free-stream vortices in the by-pass case and Kelvin–Helmholtz rolls in the separated type) that carry a significant different amount of energy. Modes obtained by the non-Euclidean POD (NE-POD) procedure (where weighted projections are considered) are shown to better extract low energy events sparse in time and space with respect to modes extracted by other variants. Moreover, NE-POD modes are further decomposed as a combination of Fourier transforms of the related temporal coefficients and the normalized data ensemble to isolate the frequency content of each mode.

A Technique for the Laboratory Determination of Recirculation in Single Needle Dialysis

1993 ◽  
Vol 16 (2) ◽  
pp. 63-70 ◽  
Author(s):  
N.A. Hoenich ◽  
P.T. Smirthwaite ◽  
C. Woffindin ◽  
P. Lancaster ◽  
T.H. Frost ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flow Rate ◽  
Experimental Results ◽  
New Technique ◽  
Treatment Efficiency ◽  
Single Lumen ◽  
Theoretical Predictions ◽  
Lumen Catheter ◽  
A New Technique

Recirculation is an important factor in single needle dialysis and, if high, can compromise treatment efficiency. To provide information regarding recirculation characteristics of access devices used in single needle dialysis, we have developed a new technique to characterise recirculation and have used this to measure the recirculation of a Terumo 15G fistula needle and a VasCath SC2300 single lumen catheter. The experimentally obtained results agreed well with those established clinically (8.5 ± 2.4% and 18.4 ± 3.4%). The experimental results have also demonstrated a dependence on access type, pump speeds and fistula flow rate. A comparison of experimental data with theoretical predictions showed that the latter exceeded those measured with the largest contribution being due to the experimental fistula.

Theoretical determination of the structures of CaSiO3 perovskites

2006 ◽  
Vol 62 (6) ◽  
pp. 1025-1030 ◽  
Author(s):  
Razvan Caracas ◽  
Renata M. Wentzcovitch
Keyword(s):  
Crystal Structure ◽  
Experimental Data ◽  
Density Functional Theory ◽  
Density Functional ◽  
Theoretical Determination ◽  
Functional Theory ◽  
Starting Point ◽  
Atomic Coordinates ◽  
The Ideal

Density functional theory is used to determine the possible crystal structure of the CaSiO3 perovskites and their evolution under pressure. The ideal cubic perovskite is considered as a starting point for studying several possible lower-symmetry distorted structures. The theoretical lattice parameters and the atomic coordinates for all the structures are determined, and the results are discussed with respect to experimental data.

Dose-window dependence on Si crystal orientation in separation by implanted oxygen substrate formation

2004 ◽  
Vol 19 (12) ◽  
pp. 3607-3613 ◽  
Author(s):  
H. Iikawa ◽  
M. Nakao ◽  
K. Izumi
Keyword(s):  
Experimental Data ◽  
Numerical Analysis ◽  
Crystal Orientation ◽  
Oxygen Ion ◽  
The Difference ◽  
First Time ◽  
Good Agreement

Separation by implemented oxygen (SIMOX)(111) substrates have been formed by oxygen-ion (16O+) implantation into Si(111), showing that a so-called “dose-window” at 16O+-implantation into Si differs from Si(100) to Si(111). In SIMOX(100), an oxygen dose of 4 × 1017/cm2 into Si(100) is widely recognized as the dose-window when the acceleration energy is 180 keV. For the first time, our work shows that an oxygen dose of 5 × 1017/cm2 into Si(111) is the dose-window for the formation of SIMOX(111) substrates when the acceleration energy is 180 keV. The difference between dose-windows is caused by anisotropy of the crystal orientation during growth of the faceted buried SiO2. We also numerically analyzed the data at different oxidation velocities for each facet of the polyhedral SiO2 islands. Numerical analysis results show good agreement with the experimental data.

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