Search

We used large-eddy simulation (LES) to numerically simulate two differently driven indoor airflows occurring in a multizone environment. In the first case, air flowed from one zone to another through a small hole driven by the total pressure difference. In the second case, unbalanced airflows arose from the buoyancy effect, which was generated by a heat source present in a specific location. To validate the LES prediction for the indoor flow analysis, we compared our simulation results with the chamber facility experimental results and other simulation results. Based on this validation, we confirmed that the LES reliably simulates indoor airflow. In addition, we discussed the flow characteristics and investigated the feasibility of modeling the flow rate through openings using an orifice formula. [ABSTRACT FROM AUTHOR]

In this paper, a novel air bleeding aerodynamic diffuser is proposed based on the study of the traditional dump diffuser. The performance and flow characteristics of these two diffusers are compared and analyzed using the numerical simulation method, which is validated by experiments. The effects of length and hole diameter on the diffuser's performance are also studied. The results reveal that, at inlet Mach numbers of 0.15, 0.20 and 0.30, compared with the dump diffuser, the total pressure loss coefficient of the new diffuser decreases by 18.52 %, 15.05 % and 40.23 %. The performance of the air bleeding aerodynamic diffuser with varing lengths has little change, which means its aerodynamic capabilities are still capable of meeting the requirements of advanced combustion chambers. As the diameter of the air bleed hole increases, the total pressure loss coefficient of the diffuser decreases and becomes gentler. [ABSTRACT FROM AUTHOR]

The present study reports the numerical investigation on the flow characteristics and heat transfer enhancement of the rib-dimpled channels. Two geometric variables were considered: the rib angle, θ, and the length between the rib center and the dimple rim, l. Nine cases were investigated by combining three different rib angles with three different lengths. Direct numerical simulations were conducted with a Reynolds number of 2800. As θ and l changed, the flow characteristics of the rib-dimpled channel were altered, which lead to different characteristics in the flow mixing and heat transfer rate. The span-wise rotating flow and the up-wash counter rotating vortices played an important role in the augmentation of heat transfer rate. The rib-dimpled channel with l = 0.15 and θ = 70° showed the maximum increase of 32 % in the volume goodness factor, in comparison with the general dimpled channel. [ABSTRACT FROM AUTHOR]

The liquid lead-bismuth pump is a core component of the main coolant circuit of the accelerator driven system. The pump performance has a significant effect on the safety and operational stability of the whole system. A liquid lead-bismuth pump was designed and the performance and flow characteristics of the pump were obtained numerically. Effects of transported medium on the performance of the pump and the forces acting on the hydraulic components were investigated. The results show that the operational performance of the pump is improved as the liquid medium of water is replaced with liquid lead-bismuth. The axial force acting on the impeller is dominated by the dynamic reverse force associated with flowing liquid lead-bismuth. Large-scale vortices formed at the bottom of the discharge chamber incur remarkable hydraulic loss. High risk of erosion exists at the outlet part of impeller blades and the inlet part of diffuser blades. [ABSTRACT FROM AUTHOR]

The aerodynamic characteristics of S-ducts with various inlet shapes were analyzed using a commercial computational fluid dynamics tool. This study aimed to investigate the influence of the aspect ratio of inlet geometry for an RAE M 2129 S-duct. The computational results were validated using experimental data from the Aircraft Research Association. The performance of the S-duct was influenced by the location of the counter-rotating vortex on the engine face. When the center of the vortex was near the starboard side, the performance was poor. By contrast, performance increased as the counter-rotating vortex moved away from the starboard side. The center of the counter- rotating vortex of the upper half semicircular S-duct was far from the starboard side, whereas that of the lower half semicircular Sduct was near the starboard side. In conclusion, S-ducts with upper half semicircular shape had better performance than those with other inlet shapes. The AR(0.75,0) case delivered the best performance, whereas the AR(1,1) case exhibited the worst. [ABSTRACT FROM AUTHOR]

Flow momentum behind a conventional nozzle is modulated by four different bluff-body cones - non-rifled, 1-rifled, 2-rifled and 3-rifled cones. This novel rifled-cone swirl generator (RCSG) includes the blockage disc and rifled bluff-body cones. The rifled bluff-body cone transforms the axial momentum (or the axial velocity) into the angular momentum (or the tangential velocity). The swirling flow is enhanced by increasing the tangential velocity of central jet. In this investigation, the carbon-dioxide (CO) is utilized as the index gas to determine the mixing index of RCSGs. Namely, the mixing index between the central CO-jet and the annular air-jet is increased using the RCSGs. The cold-flow patterns behind the rifled bluff-body cones are visualized using the smoke-wire scheme. The cold-flow patterns are categorized as - jet-flow, single-bubble and dual-bubble modes. The jet-flow mode occurs at low u. Additionally, the jet-flow and single-bubble modes are further classified as - Type-I and type-II sub-modes. The particle-image velocimetry (PIV) measures the cold-flow velocity vectors. The mixing levels of CO in the cold-flow modes are detected using a gas concentration analyzer. [ABSTRACT FROM AUTHOR]

Flow behavior for different coating conditions in in-mold coating (IMC) process was investigated. Silicon oil with viscosities of 100, 350 and 500 cps was used as model coating materials for the process and was injected into the mold cavity by using a syringe pumping machine. Flow patterns were recorded through a transparent poly (methyl methacrylate) (PMMA) window mounted in front of the mold. Flow shape index k, which is defined as the ratio of the downward flow length to the horizontal average flow length, was obtained for each testing condition. The flow characteristics, such as shape, stability, and uniformity, can be expressed in terms of the ratio k. This flow shape index analysis was used to investigate how the flow inside the mold is affected by resin viscosity, coating thickness, and injection rate, which are major parameters in the IMC process. [ABSTRACT FROM AUTHOR]

In wave motion, the water particles are known to follow orbital paths. This orbital motion was used to drive five-bladed Savonius rotors. Experiments were performed on an array of four rotors placed in a two-dimensional (2-D) wave channel. The flow around the rotors was documented using particle image velocimetry measurements. The submergence of the rotors and the distance between them were varied, and the rotational speeds of the rotors (Nn) were recorded at different wave frequencies. It was found that rotational speeds increased with an increase in the wave frequency, as it amplified the wave height that increased the kinetic energy of the particles in their orbital motion. The rotational speeds decreased when the distance between the rotors increased. High rotational speeds are recorded when the array of the rotors is placed close to the water surface at the smallest centre-to-centre distance between the rotors. [ABSTRACT FROM AUTHOR]

In a case of computer simulation used for the verification of pneumatic system performance, one of the main problems is that various parameters can be used to describe flow characteristics of the system components. Although the Standard ISO 6358 offers two parameters: the sonic conductance C and the critical static pressure ratio b, these cannot be directly utilised in the selection of elements comprising a pneumatic system. In this paper, we present two algorithms for calculating the volumetric flow rate Q N and the flow coefficient K V as a function of sonic conductance C and critical pressure ratio b (recommended by the standard) toward the improved selection of pneumatic control valves. [ABSTRACT FROM AUTHOR]

If fire breaks out on an airplane, a large amount of fire extinguishing agents should be discharged within a very short time. For effective fire extinguishing, increased discharge velocity of the fire extinguishing agents is required. This can be achieved by using a large-sized vessel in which the fire extinguishing agents are highly pressurized by noncombustible gases. It is important to understand the flow characteristics of a fire extinguishing system for optimal system design. This study reports a numerical analysis of the flow characteristics of an airplane fire extinguishing system using halon-1301 as a fire extinguishing agent. The unsteady flow model was simulated with the general-purpose software package “FLUENT”, to study the flow characteristics of the fire extinguishing agents in the system. The effects of the rupture surface area and tube diameter on the flow characteristics were investigated for optimal system design. From the analysis results, it was clarified that the characteristics of the halon discharge from the end of tube are very sensitive to the rupture surface area and significantly affected by the tube diameter. [ABSTRACT FROM AUTHOR]

Catalytic combustion is usually accomplished by a chemical reaction at the catalyst surface. Therefore, it is important that the fuel and air stream be well mixed and supplied uniformly. In this study, a perforated plate is used to enhance the mixing and flow uniformity for stable catalytic combustion. Also, a numerical simulation is performed to investigate the variation of flow characteristics according to various parameters. The results show that the uniformity of mixing and flow can be effectively improved for most of the cases by using a well-designed perforated plate. [ABSTRACT FROM AUTHOR]

The aquaculture tank is used for breeding fish in sea water which was pumped up to land. The flow characteristics in the aquaculture were investigated with varying the tank geometry and flow rate. The numerical analysis has been employed for calculating the velocity and temperature distributions in a water tank of rectangular type. The finite volume method and SIMPLE algorithm with 3-dimensional standard k-ε turbulence model were used for the numerical analysis. For comparison with experimental results, the PIV system was applied to visualize the flow patterns quantitatively. The numerical results showed good agreements with the experimental results. The mean velocity and temperature versus aquarium depth were represented for various circulating flow rates. Especially, the aquaculture environment is recommended that the aquarium depth has to be d=0.5 m, and this case is the condition of higher velocity and temperature in winter season. [ABSTRACT FROM AUTHOR]