Narrow Results

The study of the three-dimensional acoustic field inside an exhaust muffler is usually performed through the numerical solution of the linearized equations. In this paper, an alternative procedure is proposed, in which the full equations are solved in the time domain. The procedure is based on the CFD simulation of an impulsive test, so that the transmission loss may be computed and compared with measurements and other numerical approaches. Also, the details of the flow inside the muffler may be studied, both in the time and the frequency domains. The results obtained compare favorably with a conventional FEM calculation, mostly in the ability of the procedure to account for dissipative processes inside the muffler.

Mechanism analysis of frog swimming is an interesting subject in the field of biofluid mechanics and bionics. Computing the hydrodynamic forces acting on a frog is difficult due to its characteristics of explosive propulsion and large range of joint motion. To analyze the flow around the body and vortices in the wake, in this paper, the method based on Computational Fluid Dynamics (CFD) was utilized to solve the velocity and pressure distributions in the flow field and on the frog. The hydrodynamic problem during the propulsive phase of a frog, Xenopus laevis, was calculated using the CFD software FLUENT. A self-propulsion simulation was performed which computed the body velocity from the joint trajectory input and CFD solved the hydrodynamic forces, and visual CFD results of the hydrodynamic forces and flow field structures were obtained.

A liquid jet injector is a biomedical device intended for drug delivery. Medication is delivered through a fluid stream that penetrates the skin. This small diameter liquid stream is created by a piston forcing a fluid column through a nozzle. These devices can be powered by springs or compressed gas. In this study, a CFD simulation is carried out to investigate the fluid mechanics and performance of needle free injectors powered specifically by compressed air. The motion of the internal mechanisms of the injector which propels a liquid jet through an orifice is simulated by the moving boundary method and the fluid dynamics is modeled using LES/VOF techniques. In this paper, numerical results are discussed by comparing the fluid stagnation pressures of the liquid jet with previously published experimental measurements obtained using a custom-built prototype of the air-powered needle free liquid injector. Performance plots as a function of various injector parameters are presented and explained.

Agarose gel activation reaction, which is of great importance in preparing the carrier of the column packing material for blood purification, would be significantly influenced by the configuration and parameter of reactor. In order to optimize the structure design of the reactor and operating parameters of the process, the characteristics of suspension system composed of agarose gel, NaOH, water, 3-allyl bromide, and activated alumina were simulated numerically utilizing an Eulerian multiphase flow model and multi-reference frame (MRF) approach. The effect of impeller configuration was studied with three typical impellers, including Rushton disk turbine (DT), pitched blade downflow turbine (PBTD45), and pitched blade upflow turbine (PBTU45). The results showed that the optimum solid suspension was obtained using PBTD45 impeller with a diameter of 100mm and critical suspension speed of 570rpm in a 20L stirred reactor. In addition, the critical suspension speeds using the three impellers were calculated and the errors were all within the engineering allowance. Finally, the feasibility of scale-up design for agarose gel activation reactor was preliminarily discussed. The results would be useful to the optimization and scale-up of relevant reactor design.

Computational fluid dynamics (CFD) has become an essential tool for designing and optimizing the structure of blood pumps. However, it is still questionable which turbulence model can better obtain the flow information for axial flow blood pump. In this study, the axial flow blood pump was used as the object, and the influence of the common turbulence models on simulation was compared. Six turbulence models (standard $k$–$\epsilon$ model, RNG $k$–$\epsilon$ model, standard $k$–$\omega$ model, SST $k$–$\omega$ model, Spalart–Allmaras model, SSG Reynolds stress model) were used to simulate the pressure difference and velocity field of the pump. In parallel, we designed a novel drive system of the axial flow blood pump, which allowed the camera to capture the internal flow field. Then we measured the flow field in the impeller region based on particle image velocimetry (PIV). Through the comparison of experiments and simulation results, the average errors of velocity field obtained by the above models are 30.97%, 19.40%, 24.25%, 15.28%, 28.51%, 23.00%, respectively. Since the SST $k$–$\omega$ model has the smallest error, and the streamline is consistent with the experimental results, it is recommended to use SST $k$–$\omega$ model for numerical analysis of the axial flow blood pump.

An improved D’Angelo optimization framework based on the surrogate model and optimization algorithm is proposed to design and optimize a new high altitude propeller which is applied to the propulsion system of the stratospheric aircraft. The framework adopts a multilevel optimization strategy to determine a high efficiency and light weight propeller. The aerodynamic characteristics of S1223 airfoil are calculated by Computational Fluid Dynamics (CFD) method. The aerodynamic performance of the D’Angelo propeller which is obtained by the first-level optimization is predicted by Blade element momentum (BEM) theory. Then the D’Angelo propeller chord and twist angle, which are regarded as the initial conditions of the second-level optimization, are optimized to achieve the maximum efficiency by Multi-island genetic algorithm (MIGA). In addition, the non-dominated sorting genetic algorithm II (NSGA-II) is applied to maximize the propeller efficiency and minimize the propeller weight. And the Pareto frontier solutions about the efficiency and the blade area are obtained by NSGA-II. What is more, the aerodynamic characteristics of the D’Angelo propeller, the optimization propeller by MIGA, and the optimization propeller by NSGA-II are calculated by CFD simulation and compared with BEM results. It is shown that the CFD results are in fair agreement with BEM results and the aerodynamic performance of the NSGA-II propeller is prior to the MIGA propeller and is close to the D’Angelo propeller. Besides, the NSGA-II propeller is the lightest among them and can satisfy the cruise requirements of the high altitude propeller.

Droplet-based microfluidics technologies hold great attention in a wide range of applications, including chemical analysis, drug screening, and food industries. This work aimed to describe the effects of different physical properties of the two immiscible phases on droplet formation in a flow-focusing microfluidic device and determining proper flow rates to form a droplet within the desired size range. A numerical model was developed to solve the governing equations of two-phase flow and the results were validated with previous experimental results. The results demonstrate different types of droplet formation regimes from dripping to jetting and different production rates of droplets as a consequence of the impact of each property on fluid flow, including the viscosity ratio, density, interfacial tension, and the flow rate ratio. Based on the results, flow rate, viscosity, and interfacial tension strongly affect the droplet formation regime as well as its size and shape. Droplet diameter increases by increasing the dispersed to continuous phase flow rate as well as the interfacial tension while it decreases by increasing the viscosity ratio and the continuous phase density. Moreover, the formation of satellite droplets was modeled, and the effect of interfacial tension, the viscosity of the dispersed phase and the continuous phase density were found to be important on the conditions that the satellite droplets are suppressed. Since the formation of the satellite droplets induces polydispersity in droplet size, this phenomenon is avoided. Collectively, choosing appropriate aqueous and oil phases with proper physical properties is crucial in forming monodisperse droplets with defined size and shape.

The rise in urbanization has led to an increase in high-density communities. Our study drew inspiration from the fishbone structure and applied a bionic architectural layout to optimize the wind environment within the pedestrian areas of these communities. Additionally, our study delved into the intrinsic principles and simulation-based optimization methods for the wind environment in the pedestrian areas of the fishbone bionic architectural complex. Using Computational Fluid Dynamics (CFD) simulation technology, our study simulated the building models both before and after the community renovation. Furthermore, our study simulated nine architectural complex models proposed by our study, considering the architectural layout and facade height within the community. By verifying and comparing the simulation results, our study observed that the fishbone bionic architectural form significantly improved the wind environment within the community’s pedestrian areas. Regarding the facade height, our study discovered that taller architectural units should be positioned away from the prevailing wind direction to enhance the airflow within the architectural complex. This research carries substantial implications for the renovation and planning of residential communities, particularly in large urban settings with a substantial population.

This study performed a comparison between experimental and computational fluid dynamic (CFD) simulation results of boiling heat transfer coefficient of R410A in a small tube. The experimental data were obtained in the horizontal circular tubes of 3.0mm inner diameter, the length of 3000mm including: mass flux and heat flux in a range from 300kg/m²s to 600kg/m²s and from 5kW/m² to 10kW/m², respectively, and the saturation temperature constantly kept at 20${}^{\circ }$C. In the simulation procedure, the Eulerian multiphase with wall boiling were obtained. The effects of mass flux and heat flux on the heat transfer coefficient of R410A were analyzed. The comparative data between CFD and experiment was also illustrated.

The flash tank separator is one of the most important components that can be used to improve the performance of a refrigeration cycle by separating the liquid from the gas–liquid two-phase flow and providing the evaporator with only liquid refrigerant. This technique increases the effective area and enhances the heat transfer coefficient in the evaporator. To optimize the size of the vertical flash tank separator for obtaining high separation efficiency, the effect of the size of the vertical flash tank separator needs to be considered. This paper investigates the effect of the size on the liquid separation efficiency of the vertical flash tank separator. This paper also assesses the usefulness of Computational Fluid Dynamic (CFD) in flash tank design, and this is achieved through experiments and simulations on a range of relevant configurations using water as the working fluid. The results revealed that the size has a significant effect on the liquid separation efficiency, as the highest value was achieved by the largest size (VFT-V5). The CFD simulations give a good agreement with the experiments; all the simulations underestimated the liquid separation efficiency by approximately 0.02 over the range of conditions tested.

Three design enhancement options for a vertical gravitational flash tank separator were proposed and investigated in this work. Computational Fluid Dynamic (CFD) was used to assess the optimum configurations of the vertical gravitational flash tank separator. A series of experiments were performed to test the CFD proposed configurations of the enhancement design options. This paper also assessed the usefulness of CFD in flash tank design, and this is achieved through experiments and simulations on a range of relevant configurations using water as the working fluid. The results revealed that the combination of the inlet flow direction and extractor had a significant effect on the performance of the vertical flash tank separator which increased by 2%. The results also revealed that there was a good agreement between the CFD simulations and experiments; the CFD simulations underestimated the liquid separation efficiency by approximately 0.02 over the range of conditions tested.

The objective of the present research is to evaluate the thermal performance of CPC using internal fins as integral element of the triangular receiver at different mass flow rates. The influence of internal fin into triangular receiver is important geometric aspect for effective heat gain and retains thermal energy to the working fluid. The receiver without fins is taken as reference to compare the performance of receiver with different fin configurations. In this comparative analysis, the influence of concentrated solar fluxes, fin structure and mass flow rate has been taken into account to evaluate heat transfer, temperature and velocity distribution with the help of CFD to reproduce the experimental results. The realizable k-$\epsilon$ turbulence model with enhanced wall function is set to solve 3D modeling with CFD simulation. The investigation shows that, there is potential enhancement in heat transfer by the application of internal fins in triangular receiver for different flow rates.

In this study, a hybrid louver that combines a shade louver and a wind louver is developed, and its performance is verified through a comparison with other louvers. The hybrid louver is designed to prevent horizontal and vertical louvers from interfering with each other to maintain both a shading effect and a comfortable indoor wind speed. The shading performance of the hybrid louver was analyzed by the same criteria based on a study of the design for a customized shading device, which includes the energy consumption for cooling and heating, as well as indoor average wind speed analysis conducted inside a virtually designed building in the urban area of Seoul. As a result, the hybrid louver was shown to have sufficient shading and wind catcher functions. The shading effect showed ∼75% reduced energy consumption compared with the optimum shading function (100%) in an existing study, and the average indoor wind speed was ∼0.314 m/s, which is sufficiently pleasant.