Experimental Research and Numerical Analysis of Pressure Fluctuation Characteristics of Rim Driven Propulsion Pump Outlet

The pressure fluctuation characteristics of a rim driven propulsion pump are studied by an experimental method firstly, and then its unsteady inner flow is studied by numerical simulation to reveal the generating mechanism of the pressure fluctuation. In the experiment, a monitoring point was set in a downstream region with a distance of 1D (D, Diameter of impeller) to the impeller. The monitoring point’s dominant frequencies within a low frequency band are 1APF (APF, Axial Passing Frequency) and 2APF. In the numerical simulation, the main fluctuation near the impeller region appears at 1BPF (BPF, Blade Passing Frequency) and as the monitoring point moves downstream, the amplitude becomes smaller. The 1BPF fluctuation nearly disappears when the distance exceeds 1D, and the main frequency moves to 1APF and 2APF, which is in good agreement with the experimental results in the low frequency band. The transient velocity, pressure and vorticity distribution were studied to reveal the causes of 1BPF, 1APF and 2APF fluctuation. The main cause of 1BPF is the jet from the tail of the blade and the main cause of 2APF is the movement of a large-scale double vortex structure on both sides of the low-pressure zone. The movement of the vortex group near the wall may be the main cause that induces the 1APF fluctuation.

Vibration level induced by the friction of two rough surfaces weakly loaded

This paper presents an experiment to measure the vibration level generated when a light solid slides over a dry and rough surface. The experimental set-up is based on linear constant motion with speed range from 1 to 1000 mm/sec. The aim is to study the evolution of the vibration level as a function of the sliding speed and the friction area. Measurements show that the vibration level is a logarithmic increasing function of the sliding speed with a transient velocity. It is also observed that two regimes exist for the evolution of vibration level versus apparent contact area. On the one hand the vibration level is proportional to the friction area, but on the other hand this level is constant.

Temperature and Velocity Behaviour During Melting of a PCM in a Uniformly Heated Circular Cavity

This study is focused on the detailed characterization of the transient velocity and temperature fields of a PCM enclosed in a circular geometry subjected to uniform external heating. Temperature data was collected using a grid of thermocouples protruding through the transaxial wall into the PCM cavity. Particle image velocimetry (PIV) was used to collect velocity data within the melted PCM to study the buoyancy-driven convective heat transfer. Experiments were conducted at three heating conditions. The results show symmetric behaviour of temperature and velocity fields and show strong convective cells. The results also show that the velocity magnitude and its behaviour influenced the temperature field and hence the heat transfer rate.

Numerical simulation of the flow field structure of liquid nitrogen jet

Liquid nitrogen jet is regarded as an excellent technology for the well drilling and reservoir fracturing. To evaluate the flow field structure of liquid nitrogen jet, a 2-D CFD model is established. The transient velocity and temperature fields of liquid nitrogen jet is simulated. The results show that the liquid nitrogen jet also clearly presented the velocity boundary and potential core region similar to the water jet. Given the temperature difference between the jet and surrounding fluid, the liquid nitrogen jet has an obvious temperature boundary, on which the jet temperature is equal to the initial value. According to the phase of the jet, the flow structure can be divided into the liquid nitrogen jet and non-liquid nitrogen jet regions. The temperature boundary shows a larger width than the velocity boundary for liquid nitrogen jet. Moreover, both width and length of the liquid nitrogen jet region are greater than the potential core region.

Supersonic gas flow for preparation of ultrafine silicon powders and mechanochemical synthesis

We report the supersonic gas flow for crush and mechanochemical synthesis. The key instrument parameters for production of supersonic particle flow, such as annular nozzle, expansion angle and length of the accelerating duct, are theoretically designed and optimized. Based on the theoretical results, supersonic gas flow equipment is fabricated. The capacity of the present equipment for production of supersonic particle flow is demonstrated by particle image velocimetry measurement, and the maximum transient velocity of the particles achieves as much as 550 m s −1 . Additionally, the present equipment is applied for continuous and physical preparation of ultrafine Si powders with a high scalability and mechanochemical synthesis of TiO 2 and TiN x nanopowders at a high production rate.

Hydrodynamics of Droplet Impingement on a Thin Horizontal Wire

A model of droplet impacting on a thin horizontal wire is developed and numerically analyzed via level set method (LSM). Through varying the impact velocity, the flow regimes of droplet impacting on the wire are examined and analyzed. The detailed hydrodynamic behaviors including transient velocity and pressure distributions as well as the evolution of the gas-liquid interface during droplet impingement are investigated. The results indicate that the hanging mode, merging mode, and splitting mode appear during the droplet impingement on a thin horizontal wire. In merging mode, the tiny bubbles converge to big bubbles arising from the inertia difference between the liquid and the gas make. Due to the dynamic equilibrium between the friction of the thin wire and the droplet surface tension, the double reflux zone and the high-pressure zone are only observed in hanging mode rather than in merging mode and splitting mode. The flow regimes diagram depending on We and Bo is provided to represent the flow regimes of droplet impacting on a thin horizontal wire. The corresponding exponential correlations are given in form of We = aebBo to distinguish the boundaries between these droplet flow regimes.

Corrigendum

McElroy M and Keshmiri A, Impact of using conventional inlet/outlet boundary conditions on haemodynamic metrics in a subject-specific rabbit aorta, Proc IMechE, Part H: Journal of Engineering in Medicine, first published on March 25, 2017, DOI: 10.1177/0954411917699237 Following OnlineFirst publication of the article, the authors informed SAGE of an error in the transient velocity inlet profile which had been defined inaccurately due to a human error in the interpretation of clinical data in the literature. As a result of this error in boundary conditions, some of the results of transient flow computations were incorrect. A watermarked version of the first publication of the article (as first published on March 25, 2017) is attached for reference in the PDF version of this corrigendum. The authors have revised and corrected their article. The revised version of the article has been accepted following peer review and replaces the article first published on March 25, 2017. Date received: 8 August 2017; accepted: 30 November 2017 (Revised version) Date received: 29 March 2016; accepted: 21 February 2017 (Original version) The correct and citable version of the article is accessible at the following DOI: 10.1177/0954411917699237

The effect of physical preparation on the qualities of explosive power and transitional speed, and on the dribbling skills and accuracy of aiming football players in Algeria: أثر التحضير البدني على صفتي القوة الانفجارية والسرعة الانتقالية وعلى مهارتي المراوغة ودقة التصويب عند لاعبي كرة القدم في الجزائر

The researcher sought to find the relationship between physical preparation and some physical and technical characteristics of football players, where he used the experimental method As a method to study this subject and used physical and technical tests related to football and taken on a sample of nearly 14 players. The findings show that physical preparation has an effective and positive effect on transient velocity traits and explosive force. It also has an active role in the development of players technically, in improving the skills of evasion and accuracy of correction