• Journal of the Korean Society of Safety
• /
• v.15 no.3
• /
• pp.30-39
• /
• 2000

The present paper deals with the numerical simulation for the spray characteristics with swirling turbulent flows and dilution flows from swirl injectors in a simplified can type of gas turbine combustor. The main objective is to investigate the characteristics of swirling turbulent flows with dilution flows and to provide the qualitative results for the spray characteristics such as the droplet distribution and Sauter Mean Diameter(SMD). The gas-phase equations based on Eulerian approach were discretized by Finite Volume Method, together with SIMPLE algorithm and the Reynolds -Stress-Model. The liquid-phase equations based on Lagrangian method were used to predict the droplet behavior. The results of preliminary test are generally in good agreement with experimental data, and show that the anisotropy exists in the primary zone due to swirl velocity and injected air from primary injector, and then gradually decays due to turbulent mixing and consequently near-isotropy occurs in the region between primary and dilution zones. For the spray characteristics, it is indicated that the swirling flows of primary jet region increase the droplet atomization. In addition, it is showed that the swirling flows at the inlet region lead the air-fuel mixture to be distributed near the igniter and can significantly affect the spray behavior in the primary jet region.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.5
• /
• pp.448-454
• /
• 2019

This paper presents a high-efficiency design technique for developing the serialized models of a single-channel pump based on the diameter, flow rate and head as the main performance parameters. The variation in pump performance by changing of the single-channel pump geometry was predicted based on computational fluid dynamics (CFD). Numerical analysis was conducted by solving three-dimensional steady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model. The tendencies of the hydraulic performance depending on the pump geometry scale were analyzed with the fixed rotational speed. These performances were expressed and evaluated as the functionalization for designing the serialized models of a single-channel pump in this work.

• New & Renewable Energy
• /
• v.20 no.2
• /
• pp.35-43
• /
• 2024

A pump turbine is a technically matured option for energy production and storage systems. At the off-design operating range, the pump turbine succumbed to flow instabilities, which correlated with the pump turbine geometry. A low specific speed pump turbine was designed and modified according to the impeller blade angle. Reynolds-Average Navier-Stokes is carried out with a shear stress transport turbulence model to evaluate the detailed flow characteristics in the pump turbine. The impeller blade inlet angle (𝛽₁) and outlet angle (𝛽₂) are used to evaluate hydraulic loss in the pump turbine. When 𝛽₁ changed from low to high value, the maximum efficiency is increased by 4.75% in turbine mode. The S-Curve inclination is reduced by 8% and 42% for changes in 𝛽₁ and 𝛽₂ from low to high values, respectively. At α = 21°, the shock loss coefficient (𝜁_s) is reduced by 16% and 19% with increases of 𝛽₁ and 𝛽₂ from low to high values, respectively. When 𝛽₁ and 𝛽₂ values increased from low to high, the impeller friction coefficient (𝜁_f) increased and decreased by 20% and 8%, respectively. Hence, the high 𝛽₂ effectively reduced the loss coefficient and S-Curve inclination.

• Transactions of the Korean hydrogen and new energy society
• /
• v.31 no.3
• /
• pp.328-336
• /
• 2020

In the Francis turbine, the leakage flow through the runner gaps which are between the runner and the stator structure influences the internal flow and hydraulic performance. Thus, the investigation for the flow characteristics induced by the runner gaps is important. However, the runner gaps are often disregarded by considering the time and cost of the numerical analysis. Therefore, in this study, the flow characteristics according to runner gaps of the Francis turbine model were investigated including the leakage flow of the runner cone. The three-dimensional unsteady Reynolds-averaged Navier-Stokes analyses were conducted using a scale-adaptive simulation shear stress transport as a turbulence model for observing the influence of the leakage flow on the internal flow and hydraulic performance. The efficiencies were decreased slightly with runner gaps; and the complicated flows were captured in the gaps.

• International Journal of Fluid Machinery and Systems
• /
• v.7 no.1
• /
• pp.34-41
• /
• 2014

Computational fluid dynamics (CFD) and particle image velocimetry (PIV) are commonly used techniques to evaluate the flow characteristics in the development stage of blood pumps. CFD technique allows rapid change to pump parameters to optimize the pump performance without having to construct a costly prototype model. These techniques are used in the construction of a bi-ventricular assist device (BVAD) which combines the functions of LVAD and RVAD in a compact unit. The BVAD construction consists of two separate chambers with similar impellers, volutes, inlet and output sections. To achieve the required flow characteristics of an average flow rate of 5 l/min and different pressure heads (left - 100mmHg and right - 20mmHg), the impellers were set at different rotating speeds. From the CFD results, a six-blade impeller design was adopted for the development of the BVAD. It was also observed that the fluid can flow smoothly through the pump with minimum shear stress and area of stagnation which are related to haemolysis and thrombosis. Based on the compatible Reynolds number the flow through the model was calculated for the left and the right pumps. As it was not possible to have both the left and right chambers in the experimental model, the left and right pumps were tested separately.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.12
• /
• pp.1653-1661
• /
• 2012

In this study, the pressure drop changes and structural characteristics of a SMART rod bundle under the effect of a coolant were investigated. The turbulence model of the BSL Reynolds stress model was used to model the coolant flow, and a fluid solid interaction simulation was conducted. First, fuel rod vibration analysis was performed to confirm the natural frequency of the fuel rod, which was supported by spacer grid assemblies, and this was compared with experimental results. From the experimental results, the natural frequency was found to be 48 Hz, and the error compared with the simulation results was 2%. The pressure drop at the rod bundle was calculated and compared with the experimental data; it showed an error of 8%, demonstrating the simulation accuracy. In the flow analysis, the flow velocity and secondary flow at different domains were calculated, and vortex generation was also observed. Finally, through the fluid solid interaction analysis, the fuel rod displacements caused by flow-induced vibrations were calculated. Then, calculated displacement PSD at maximum displacement happed point.

• Journal of Aerospace System Engineering
• /
• v.13 no.1
• /
• pp.1-10
• /
• 2019

The flow characteristics in a stirred tank are very useful in a wide variety of industrial applications. Generally, the flow pattern, power consumption and mixing time in stirred vessels depend not only on the design of the impeller, but also on the tanks' geometry and internal structure. In this study, the analysis of an unstable and unsteady complicated flow characteristics generated by the interaction between the baffle shape and impeller were performed using the ANSYS FLUENT LES Turbulence Model. The study compared the predictions of CFD with the interaction between two types of rotating impellers (axial and radial flows) and the shapes of three baffles. The results of the comparison verified that the design model showed a relatively efficient trend in the mixing flow fields and characteristics around the impeller and baffles during agitation.

• Journal of Convergence for Information Technology
• /
• v.9 no.8
• /
• pp.155-163
• /
• 2019

Laminar mixed convection of a nanofluid consists of water and $Al_2O_3$ in a horizontal circular tube has been studied numerically. Two-phase mixture model has been used to investigate hydrodynamic and thermal behaviors of the nanofluid with variables physical properties. Three dimensional Navier-Stokes, energy and volume fraction equations have been discretized using the finite volume method. The Brownian motions of nanoparticles have been considered to determine the thermal conductivity and dynamic viscosity of $Al_2O_3$-Water nanofluid, which depend on temperature. The calculated results show good agreement with the previous numerical data. Results show that in a given Reynolds number (Re), increasing solid nanoparticles volume fraction and Richardson number (Ri) increases the convective heat transfer coefficient and wall shear stress.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.1
• /
• pp.55-68
• /
• 2020

In order to investigate the hydraulic characteristics of a boundary layer streaming over the beach cusps appeared in swells prevailing mild seas, we numerically simulated the shoaling process of Edge waves over the beach cusp. Synchronous Edge waves known to sustain the beach cusps could successfully be duplicated by generating two obliquely colliding Edge waves in front of beach cusps. The amplitude A_B and length L_B of Beach Cusp were elected to be 1.25 m and 18 m, respectively based on the measured data along the Mang-Bang beach. Numerical results show that boundary layer streaming was formed at every phase of shoaling process without exception, and the maximum boundary layer streaming was observed to occur at the crest of sand bar. In RUN 1 where the shortest waves were deployed, the maximum boundary layer streaming was observed to be around 0.32 m/s, which far exceeds the amplitude of free stream by two times. It is also noted that the maximum boundary layer streaming mentioned above greatly differs from the analytical solution by Longuet-Higgins (1957) based on wave Reynolds stress. In doing so, we also identify the recovery procedure of natural beaches in swells prevailing mild seas, which can be summarized such as: as the infra-gravity waves formed in swells by the resonance wave-wave interaction arrives near the breaking line, the sediments ascending near the free surface by the Phase II waves orbital motion were carried toward the pinnacle of foreshore by the shoreward flow commenced at the steep front of breaking waves, and were deposited near the pinnacle of foreshore due to the infiltration.

• Wind and Structures
• /
• v.35 no.1
• /
• pp.1-20
• /
• 2022

This research work presents an experimental study's outcomes to reveal the impact of an O-ring on the flow control over a sphere placed in a turbulent boundary layer. The investigation is performed quantitatively and qualitatively using particle image velocimetry (PIV) and dye visualization. The sphere model having a diamater of 42.5 mm is located in a turbulent boundary layer flow over a smooth plate for gap ratios of 0≤G/D≤1.5 at Reynolds number of 5 × 10³. Flow characteristics, including patterns of instantaneous vorticity, streaklines, time-averaged streamlines, velocity vectors, velocity fluctuations, Reynolds stress correlations, and turbulence kinetic energy (), are compared and discussed for a naked sphere and spheres having O-rings. The boundary layer velocity gradient and proximity of the sphere to the flat plate profoundly influence the flow dynamics. At proximity ratios of G/D=0.1 and 0.25, a wall jet is formed between lower side of the sphere and flat plate, and velocity fluctuations increase in regions close to the wall. At G/D=0.25, the jet flow also induces local flow separations on the flat plate. At higher proximity ratios, the velocity gradient of the boundary layer causes asymmetries in the mean flow characteristics and turbulence values in the wake region. It is observed that the O-ring with various placement angles (𝜃) on the sphere has a considerable alteration in the flow structure and turbulence statistics on the wake. At lower placement angles, where the O-ring is closer to the forward stagnation point of the sphere, the flow control performance of the O-ring is limited; however, its impact on the flow separation becomes pronounced as it is moved away from the forward stagnation point. At G/D=1.50 for O-ring diameters of 4.7 (2 mm) and 7 (3 mm) percent of the sphere diameter, the -ring exhibits remarkable flow control at 𝜃=50° and 𝜃=55° before laminar flow separation occurrence on the sphere surface, respectively. This conclusion is yielded from narrowed wakes and reductions in turbulence statistics compared to the naked sphere model. The O-ring with a diameter of 3 mm and placement angle of 50° exhibits the most effective flow control. It decreases, in sequence, streamwise velocity fluctuations and length of wake recovery region by 45% and 40%, respectively, which can be evaluated as source of decrement in drag force.