Large eddy simulation study of a Venturi cavitation nozzle with two auxiliary flow channels

The N-S equations formulated with the orthogonal curvilinear coordinate system have been solved numerically for periodic viscous flows through a circular hole driven by fluctuating far field pressure. The flow patterns and acoustic impedance of the circular hole are investigated for various combinations of pressure/viscous force ratio, fluctuating frequency and hole edge thickness. For the high frequency and low pressure range, there is no laminar separation, and the resistance is independent of the periodic pressure amplitude. For the intermediate frequency and pressure range, an attached separation bubble is generated near the downstream side of the hole edge, and the resistance is larger for smaller hole edge thickness and smaller force ratio. For the low frequency and high pressure range, the separation bubble grows to a detached vortex ring and the resistance is proportional to the square root of the pressure amplitude but independent of the viscousity of the fluid and almost invariant with the frequency.

Anthracite coal-derived activated carbon as an effectiveness adsorbent for superior gas adsorption and CO2 / N2 and CO2 / CH4 selectivity: Experimental and DFT study

<p>To provide calibration services for pressure measuring devices, SNSU-BSN has several piston-cylinder standard that may traceable to different National Metrology Institute (NMIs). Non-full range calibration of pressure balance has been performed to evaluate the consistency of calibration results between those standard, especially for establishing self-traceability in the future. In this research, a piston-cylinder unit S/N 1926 with medium pressure range of 1750 kPa, was calibrated with low pressure range S/N 978 of 350 kPa and high pressure range S/N 1054 of 7000 kPa. The calibration was performed with cross-float method to evaluate the effective area of piston-cylinder at null pressure and reference temperature of 20⁰C (<em>A<sub>0,20</sub></em>) and distortion coefficient (λ) as the 1926 main parameters. The obtained value, respectively are (1.961 166 × 10<sup>-4</sup> ± 4.4 × 10<sup>-9</sup>) m<sup>2 </sup>and (-1.67 × 10<sup>-12</sup> ± 9.4 × 10<sup>-13</sup>) Pa<sup>-1 </sup>from 978 and (1.961166 × 10<sup>-4</sup> ± 5.1 × 10<sup>-9</sup>) m<sup>2</sup> and (-1.58 × 10<sup>-12</sup> ± 8.4 × 10<sup>-13</sup>) Pa<sup>-1 </sup>from 1054. The result of 1926 from both methods shows good conformity with Normalized Error (En) of 0.0007 and 0.069, respectively. Linearity of effective area changes to the pressure is very consistent in both low and high pressure range. Validation results by using PTB-Germany results, shows the relative different for <em>A<sub>0</sub></em> and <em>λ</em> obtained are less than 0,1 × 10<sup>-6</sup> and 6%,respectively. Therefore, the pneumatic pressure balance of SNSU-BSN is traceable, consistent with each other and capable for disseminating the pressure unit along all primary pressure standard owned with high agreement compared to those of other advance NMIs.</p>

Numerical research of diesel spray and atomization coupled cavitation by Large Eddy Simulation (LES) under high injection pressure

This article reports numerical computations of a turbulent round jet of transcritical fluid (low temperature nitrogen injected under high pressure conditions) surrounded by the same fluid at rest under supercritical conditions (high temperature and high pressure) and submitted to transverse acoustic modulations. The numerical framework relies on large eddy simulation in combination with a real-gas description of thermodynamics and transport properties. A stationary acoustic field is obtained by modulating the normal acoustic velocity at the lateral boundaries of the computational domain. This study specifically focuses on the interaction of the jet with the acoustic field to investigate how the round transcritical jet changes its shape and mixes with the surrounding fluid. Different modulation amplitudes and frequencies are used to sweep a range of conditions. When the acoustic field is established in the domain, the jet length is notably reduced and the jet is flattened in the spanwise direction. Two regimes of oscillation are identified: for low Strouhal numbers a large amplitude motion is observed, while for higher Strouhal numbers the jet oscillates with a small amplitude around the injector axis. The minimum length is obtained for a Strouhal number of 0.3 and the jet length increases with increasing Strouhal numbers after reaching this minimum value. The mechanism of spanwise deformation is shown to be linked with dynamical effects resulting from reduction of the pressure in the transverse direction in relation with increased velocities on the two sides of the jet. A propagative wave is then introduced in the domain leading to similar effects on the jet, except that a bending is also observed in the acoustic propagation direction. A kinematic model, combining hydrodynamic and acoustic contributions, is derived in a second stage to represent the motion of the jet centerline. This model captures details of the numerical simulations quite well. These various results can serve to interpret observations made on more complex flow configurations such as coaxial jets or jet flames formed by coaxial injectors.

Saline contrast enhancement of tricuspid regurgitant jets detected by doppler color flow imaging

In this paper, we have improved a cavitation model implemented in “Front Flow/Blue (FFB)”, which is a solver of turbulent flows using the large-eddy simulation (LES) technique with high accuracy. To improve the cavitation model, we have carried out a survey of conventional cavitation models and performed a trade-off between the models based on some evaluation points such as accuracy, achievement, future potential, and computational cost. In the new cavitation model, the surface area of cavitation bubbles in each cell is also solved in addition to the volume fraction of the bubbles. Although the validation is in progress, the new cavitation model is expected to be useful to reproduce a detailed cavitation structure.

To study the instability of a Francis turbine at off-design operating condition, a hydraulic model was established and the flow characteristics at the off-design point were studied based on large eddy simulation (LES). The simulation was conducted for both single phase model and cavitation model. The results were compared with the experimental data. Results show that the simulation based on cavitation model can capture more channel vortex structures than single phase calculation. The result of vortex rope by cavitation model is similar to the experimental result. The dominant frequency can be obtained by these two methods, while the result based on cavitation model can capture the high frequency component at the inlet of draft tube. Great difference can be seen from the internal flow of the two simulation results. These conclusions can provide a basis for the study of instability of Francis turbine.

An experimental investigation of the mean velocity profiles is presented for the jet issuing into a quiescent ambient air from rectangular exits. Exits having small aspect ratios and differing in shape are utilized. The experimental results of mean properties such as axial velocity decay, half-width, static pressure, etc. are reported. It is found that some of the mean properties show remarkable changes according to the exit shape. Attaching a short length of uniform cross section above the exit plane, the gross appearance of the jet issuing from a smoothly contracted nozzle becomes similar to that issuing from a long channel. An empirical formula, taking the characteristic length as the square root value of the exit area, is presented for axial velocity decay and jet spread in an axisymmetric decay region.

Cavitation today is a very important problem that is solved by means of experimental and mathematical methods. The article deals with the generation of cavitation in convergent divergent nozzle of rectangular cross section. Measurement of pressure, flow rate, temperature, amount of dissolved air in the liquid and visualization of cavitation area using high-speed camera was performed for different flow rates. The measurement results were generalized by dimensionless analysis, which allows easy detection of cavitation in the nozzle. For numerical simulation the multiphase mathematical model of cavitation consisting of water and vapor was created. During verification the disagreement with the measurements for higher flow rates was proved, therefore the model was extended to multiphase mathematical model (water, vapor and air), due to release of dissolved air. For the mathematical modeling the multiphase turbulence RNG k-ε model for low Reynolds number flow with vapor and air cavitation was used. Subsequently the sizes of the cavitation area were verified. In article the inlet pressure and loss coefficient depending on the amount of air added to the mathematical model are evaluated. On the basis of the approach it may be create a methodology to estimate the amount of released air added at the inlet to the modeled area.

Automotive cabin vent: Comparison of RANS and LES approaches with analytical-empirical equations and their validation with experiments using Hot-Wire Anemometry

The fact that the spray characteristics of automotive fuel injectors of direct injection type are substantially influenced by cavitation in the nozzles is widely known. Many researchers have been engaged in understanding the relation between a cavitating flow and characteristics of fuel spray using a numerical simulation till now. In a free surface flow analysis and a multiphase flow analysis, advantages of using a particle-based meshless method are utilized. However, particle-based meshless methods have not been used to simulate cavitation. In this study, the cavitation in a two-dimensional nozzle and the water jet were simulated using Moving Particle Semi-implicit (MPS) method employing a cavitation model. The simulation results are relatively close to experimental data.

The influence of lead nitrate, red lead, lead chromate, lead floride and lead carbonate on the combustion behaviour of double base propellants in the pressure range-35-140kg/cm /sup 2/ was studied. While all these compounds increased burning rates in lower pressure range (35-60 kg/cm/sup 2/) and higher pressure range (120-140 kg/cm/sup 2/), only lead chromate and lead fluoride were effective in the intermediate pressure range of 60-105 kg/cm/sup 2/. None of these compounds were effective as platonizer, except lead fluoride, which lowered n value to 0.34 in the lower pressure range. Addition of carbon black along with lead compounds raised burning rates further and reduced n values significantly in the higher pressure regins. A probable mechanism on the role of lead compounds studied has been suggested based on burning rate and DTA results.

We have extended measurable pressure range of the thin film Pirani vacuum sensor that is still sensitive above 1×105 Pa (1 atmosphere). In our thin film Pirani vacuum sensor, our proposed temperature difference sensor of the short circuit Seebeck-current detection type thermocouple is used in order to get extremely high sensitivity, especially both in very low pressure range and in higher pressure range than 1×104 Pa. In our new pressure sensor the cantilever type sensing region, in which a microheater and two thermocouples are formed to measure the temperature difference, is adopted. Therefore, we can use the null method to measure very small pressure accurately in the high vacuum range (low pressure range). On the other hand in the higher pressure than 1×104 Pa., we could expand the pressure range by adoption of the vibration of the sensing cantilever based on the sudden heating due to the exchange of heater driving. We have achieved much wider measurable pressure range over 8 digits by use of our new simple thin film Pirani vacuum sensor than that of the traditional one.

Triboelectric sensor array for internet of things based smart traffic monitoring and management system