Journal of Applied Fluid Mechanics

Ventricular assist devices (VADs) have emerged as an effective clinical tool for offering crucial aid to patients suffering with heart failure. To achieve optimal performance that matches a healthy ventricle, precise design and a thorough understanding of hydraulic and clinical factors are crucial. This research paper presents a comprehensive analysis using computational fluid dynamics (CFD) software ANSYS Fluent at different range of rotational speed and flow rate to examine the performance of an axial blood pump with three different straightener designs: conical, cylindrical, and paraboloid. The primary objective is to assess the impact of these straightener designs on the overall performance of the axial blood pump. Initially, the base axial pump employed conical straightener designs, which were subsequently modified to paraboloid and cylindrical shapes to evaluate their performance. Consistently, the results demonstrated that the paraboloid design outperformed the other designs. Specifically, the axial blood pump equipped with a paraboloid straightener exhibited an increased pressure head and lower intensity of turbulent kinetic energy compared to the other two designs. Additionally, the wall shear stress in the impeller region was lower in the paraboloid design. By employing CFD tool, this study provides valuable insights into the performance of different straightener designs for axial blood pumps. The findings highlight the superiority of the paraboloid design in terms of pressure head and wall shear stress reduction. These results contribute to enhancing the effectiveness and efficiency of left ventricular assist devices (LVADs), ultimately benefiting patients with heart failure.

Cyclone separators are commonly used in pneumatic conveyor systems due to their low cost and ability to separate solid particles from gas streams. Understanding pressure drop in cyclone separators is crucial for designing, developing, and optimizing efficient cyclone separators for pneumatic conveyors. The swirling motion within the cyclone during particle-gas separation can cause a pressure drop in the pneumatic conveyor. This study investigates the pressure drop across cyclone separators in pneumatic conveyor systems for Teff grain, both experimentally and computational fluid dynamics (CFD) with discrete particle modeling (DPM) simulation. The study utilized the Lapple cyclone separator model and examined the effects of varying cyclone size (0.75D, 0.9D, and 1D for D=200mm), inlet air velocity (10m/s, 14m/s, 18m/s, 22m/s), and material mass flow rate (0.009kg/s, 0.03kg/s, 0.044kg/s, 0.067kg/s) on the pressure drop across the cyclone separator. The results show that there is strong agreement between experimental and CFD-DPM simulation results. The simulation results accurately represent experimental results, with R-squared value of 0.99 and a residual sum of squares of 38.018. Furthermore, the best curve fit was obtained between the power losses due to pressure drop across the cyclone separator and air mass flow rate. These findings demonstrate that the pressure drop and associated power losses across cyclone separators in pneumatic Teff grain conveyors can be effectively determined using both experimental and simulation methods. This finding can inform the design and optimization of efficient cyclone separators for pneumatic Teff grain conveyor systems.

Butterfly valves are critical control equipment widely used in transmission systems across various fields, including energy, water conservancy, materials and chemical industries, metallurgy, and aerospace engineering. Cavitation, induced when the local pressure is decreased to saturated vaporization pressure, is a common phenomenon in butterfly valves and causes severe damage to valve components. Numerical studies were conducted to explore the progression of dynamic cavitation in a butterfly valve under different actual conditions by using Large Eddy Simulation (LES) coupled with Schnerr-Sauer cavitation model.  The detailed evolution process of generation, development, and collapse was discussed by analyzing the corresponding vapor volume fraction. With the increase of valve opening, there is a corresponding increase in cavitation volume, leading to the rise of disturbance coefficient in full flow field as well as the decrease of shedding frequency of cavitation. The decline of shedding frequency of cavitation exhibits a sudden and pronounced drop at valve opening degree of 60%, which can be attributed to a shift in cavitation shedding behavior from unilateral to bilateral shedding. Periodic changes in cavitation evolution and the presence of attached cavitation on the upper surface of valve plate are obtained and discussed in detail. A comparative analysis of vortex distribution and structure within the flow field reveals insights into the spatial and temporal correlation between cavitation and vortices. The present study of the cavitation mechanism and the in-depth exploration of the evolution law of cavitation provide a clearer understanding of cavitation phenomenon, offering a reference for the structural optimization of butterfly valve in cavitation inhibition.

In this study, a numerical simulation of the static leakage of a subway vehicle was conducted, based on the turbulence model of k-ω Shear Stress Transport (SST). The impact of the leak hole thickness and of the slenderness ratio, on the airtightness of the vehicle is analyzed with a single leak hole, as is the influence of the number, location, slenderness ratio, and area ratio of leak holes, on the airtightness of a train with multiple leak holes. The relative errors of the numerical simulation results are smallest when the leak hole slenderness ratio is 1:16. The relative errors in cases of a single leak hole, and of multiple leak holes are 4.93% and 3.68%, respectively. The pressure relief time first decreases, and then increases as the thickness of the leak hole increases, and is the smallest when the leak is 200 mm in thickness. Keeping the total area of leak holes unchanged, the location and number of leak holes have little impact on the pressure relief time. When door and window leak holes have different thicknesses, changing the area ratio of the door and window leak holes increases the pressure relief time, by a maximum of 1.23 seconds.

Given the vast global capacity of wind turbines, even minor enhancements in their overall performance can substantially increase energy production. To achieve this, several techniques have been developed and implemented commercially to create advanced blades with improved efficiency. However, the fixed aerodynamic shape of these blades imposes certain constraints. This study conducts a numerical analysis of a 660 kW wind turbine, revealing that under specific operating conditions, the blades experience off-design conditions, leading to performance degradation. Simulations indicate that because the blades are designed for a single operating point, flow separation occurs on some sections of the blade surface in other situations. Further investigation demonstrates that the fixed geometry of the blades hinders the flow’s ability to adapt to their shape. To address this challenge, the method of boundary layer suction is proposed. Results indicate that by applying an appropriate level of suction intensity, the aerodynamic performance of the rotor can be enhanced by up to 8% under the specified working conditions by facilitating flow reattachment at the inboard section.