• The KSFM Journal of Fluid Machinery
• /
• v.13 no.2
• /
• pp.59-64
• /
• 2010

A design method of Sirocco fan is developed for constructing 3-D impeller and scroll geometries, and for predicting both the aerodynamic performance and the noise characteristics of the designed fan. The aerodynamic blading design of fan is conducted by blade angle, camber line determinations and airfoil thickness distribution, and then the scroll geometry of fan is designed by using logarithmic spiral. The aerodynamic performance of designed fan is predicted by the meanline analysis with flow blockage, slip and pressure loss correlations. Based on the predicted performance data, fan noise is predicted by two models for cutoff frequency and broadband noise sources. The present predictions for the performance and the noise level of actual fans are well agreed with measurement results.

• Journal of the Society of Naval Architects of Korea
• /
• v.53 no.6
• /
• pp.465-472
• /
• 2016

A study was carried out to investigate typical features of natural supercavitation generated behind axisymmetric bodies such as disk and cone shaped cavitators. Main focuses of the study were to observe formation process of the supercavity and to measure drag forces acting on cavitators. Experiments were carried out at the cavitation tunnel of the Chungnam National University (CNU-CT), which has a capability to make sufficient flow speed for supercavitation experiments and to remove broken cavity bubbles coming back to the test section. Blockage effects on supercavity dimensions were evaluated and an effort was made to correlate tunnel experiments with unbounded flow. On the basis of experimental and numerical results, geometrical features of supercavities and characteristics of drag forces were examined and their relations were proposed.

• 유체기계공업학회:학술대회논문집
• /
• 1999.12a
• /
• pp.301-308
• /
• 1999

The present study investigates numerically particle laden flow through compressor cascades and a rocket nozzle. Engines are affected by various particles which are suspending in the atmosphere. Especially in the case of aircraft aviating in volcanic, industrial and desert region including many particles, each components of engine system are damaged severely. That damage modes are erosion of compressor blading and rotor path components, partial or total blockage of cooling passage and engine control system degradation. Numerical prediction and experimental data, erosion rates are predicted for two materials - ceramic, soft metal - on compressor blade surface. Aluminum oxide ($Al_2O_3$) Particles included in solid rocket propelant make ablative the rocket motor nozzle and imped the expansion processes of propulsion. By the definition of particle deposition efficiency, characteristics of particles impaction are considered quantitatively Stoke number is defined over the various particle sizes and particle trajectories are treated by Lagrangian approach. Particle stability is considered by definition of Weber number in rocket nozzle and particle breakup and evaporation is simulated in a rocket nozzle.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.8 s.239
• /
• pp.948-955
• /
• 2005

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the internal flow in a low-speed axial compressor operating at the design condition($\phi=85\%$) and near stall condition($\phi=65\%$). At the design condition, the flows in the axial compressor show, independent of the inlet boundary layer thickness, similar characteristics such as the pressure distribution, size of the hub comer-stall, tip leakage flow trajectory, limiting streamlines on the blade suction surface, etc. However, as the load is increased, the hub corner-stall grows to make a large separation region at the junction of the hub and suction surface for the inlet condition with thick boundary layers at the hub and casing. Moreover, the tip leakage flow is more vortical than that observed in case of the thin inlet boundary layer and has the critical point where the trajectory of the tip leakage flow is abruptly turned into the downstream. For the inlet condition with thin boundary layers, the hub corner-stall is diminished so it is indistinguishable from the wake. The tip leakage flow leans to the leading edge more than at the design condition but has no critical point. In addition to these, the severe reverse flow, induced by both boundary layer on the blade surface and the tip leakage flow, can be found to act as the blockage of flows near the casing, resulting in heavy loss.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.12
• /
• pp.924-930
• /
• 2008

Immersed boundary method (IBM) is the most effective method to overcome the disadvantage of LBM (Lattice Boltzmann Method) related to the limitation of the grid shape. IBM also make LBM possible to simulate flow over complex shape of obstacle without any treatment on the curved boundary. In the research, IBLBM was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of IBLBM on the moving obstacle near the wall, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of moving cylinder in the channel using IBLBM. The simulations were performed in a moderate range of Reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag and lift coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical Reynolds number for vortex shedding is Re=50 and the result is the same as the case of fixed cylinder. As the cylinder approaching to a wall (${\gamma}<2.5$), the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. When the cylinder is very closed to the wall, ${\gamma}<0.6$, the cylinder acts like blockage to block the flow between the cylinder and wall so that the vortex developed on the upper cylinder elongated and time averaged lifting and drag coefficients abruptly increase.

• Wind and Structures
• /
• v.29 no.6
• /
• pp.405-416
• /
• 2019

Aerodynamic characteristic of a small scale wind turbine under the influence of an incoming uniform wind field is studied using k-ω Shear Stress Transport turbulence model. Firstly, the lift and drag characteristics of the blade section consisting of S826 airfoil is studied using 2D simulations at a Reynolds number of 1×10⁵. After that, the full turbine including the rotational effects of the blade is simulated using Multiple Reference Frames (MRF) and Sliding Mesh Interface (SMI) numerical techniques. The differences between the two techniques are quantified. It is then followed by a detailed comparison of the turbine's power/thrust output and the associated wake development at three tip speeds ratios (λ = 3, 6, 10). The phenomenon of blockage effect and spatial features of the flow are explained and linked to the turbines power output. Validation of wake profiles patterns at multiple locations downstream is also performed at each λ. The present work aims to evaluate the potential of the numerical methods in reproducing wind tunnel experimental results such that the method can be applied to full-scale turbines operating under realistic conditions in which observation data is scarce or lacking.

• The KSFM Journal of Fluid Machinery
• /
• v.8 no.4 s.31
• /
• pp.39-47
• /
• 2005

The present study has been performed to investigate the influences of rectangular fins on heat transfer in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system with initial crossflow, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. The crossflow passes between the plates, and various rectangular fins are installed on the plates. Reynolds number based on the hole diameter is fixed to 10,000 and the flow rate of crossflow is changed from 0.5 to 1.5 times of that of the impinging jet. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. Also to analyze the flow characteristics, a numerical calculation is performed. When rectangular fins are installed, the flow and heat transfer pattern is changed greatly from the case without fins. In the injection hole region, the jet impinges on effusion plate without deflection and wall jet spreads symmetrically. In the effusion region, the crossflow accelerates due to the decrease of cross-sectional area in the channel. Local heat/mass transfer coefficients are enhanced significantly compared to the case without fins. As the blowing ratio increases, the effect of rectangular fins against the crossflow becomes more significant and then the higher average heat/mass transfer coefficients are obtained than the case without fins. However, the increase of blockage effect gives more pressure loss in the channel.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.8
• /
• pp.1091-1096
• /
• 2012

The aerodynamic characteristics of circular cylinder in a channel are studied to make clear the flow feature by solving the Navier-Stokes equation based on the finite volume method with unstructured grids. Reviews are made on with the vorticity, velocity, dynamic pressure, residual and drag, where the Reynolds numbers are 50 and 100. The flows for $Re{\succeq}50$ shows the vortex shedding in the wake, and the result is the same as the case of moving cylinder. The ground effect of flat bottom results in the growth of vortex, being generated in the upper side of the cylinder and elongated in the rear. As the cylinder approaches to wall, for example 0.6, the cylinder plays as a role of blockage to obstruct the flow between the cylinder and wall. The drag coefficients are compared with others' results to confirm the validity of the present numerical simulation.

• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.4
• /
• pp.614-622
• /
• 2017

The characteristics of aerodynamic drag for Transonic Vehicle in Evacuated Tube was investigated using computational fluid dynamics. At first, parametric study on the system was performed according to the Mach number of the vehicle's speed ($Mach_v$), evacuated pressure of the tube ($Pre_t$), and blockage ratio (BR) between the vehicle and tube via axisymmetric flow analysis; the $Mach_v$ ranged from 0.3 to 1.0. The $Pre_t$ was 100, 1,000 and 10,000 Pa and the BR was 0.1, 0.2, and 0.4. In the calculations, the aerodynamic drag of the vehicle was larger when the BR and the pressure became larger. Concerning the $Mach_v$, the drag coefficient ($C_d$) became the maximum when the $Mach_v$ was near the Kantrowitz limit and decreased, which showed the typical transonic flow pattern. Then, three dimensional flow analysis was performed by changing the $Mach_v$ from 0.3 to 1.0 and setting the BR and the $Pre_t$ as 0.34 and 100 Pa, respectively by referring the Hyperloop Alpha documentation. From the calculations, the $C_d$ from three dimensional flow simulations were somewhat larger than those of axisymmetric ones because of the eccentricity of the vehicle inside the tube. However, the pattern of $C_d$ according to the $Mach_v$ was compatible with that of axisymmetric ones.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.4 no.4
• /
• pp.477-487
• /
• 2012

We investigated the aerodynamic characteristics of a three-dimensional (3D) wing with an endplate in the vicinity of the free surface by solving incompressible Navier-Stokes equations with the turbulence closure model. The endplate causes a blockage effect on the flow, and an additional viscous effect especially near the endplate. These combined effects of the endplate significantly reduce the magnitudes of the velocities under the lower surface of the wing, thereby enhancing aerodynamic performance in terms of the force coefficients. The maximum lift-to-drag ratio of a wing with an endplate is increased 46% compared to that of wing without an endplate at the lowest clearance. The tip vortex of a wing-with-endplate (WWE) moved laterally to a greater extent than that of a wing-without-endplate (WOE). This causes a decrease in the induced drag, resulting in a reduction in the total drag.