• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.155-168
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• 2008

This paper investigates a variable geometry (VG) mixed flow turbine with a novel, purposely designed pivoting nozzle vane ring. The nozzle vane ring was matched to the 3-dimensional aspect of the mixed flow rotor leading edge with lean stacking. It was found that for a nozzle vane ring in a volute, the vane surface pressure is highly affected by the flow in the volute rather than the adjacent vane surface interactions, especially at closer nozzle positions. The performance of the VG mixed flow turbine has been evaluated experimentally in steady and unsteady flow conditions. The VG mixed flow turbine shows higher peak efficiency and swallowing capacity at various vane angle settings compared to an equivalent nozzleless turbine. Comparison with an equivalent straight vane arrangement shows a higher swallowing capacity but similar efficiencies. The VG turbine unsteady performance was found to deviate substantially from the quasi-steady assumption compared to a nozzleless turbine. This is more evident in the higher vane angle settings (smaller nozzle passage), where there are high possibility of choking during a pulse cycle. The presented steady and unsteady results are expected to be beneficial in the design of variable geometry turbochargers, especially the ones with a mixed flow turbine.

• International Journal of Automotive Technology
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• v.8 no.5
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• pp.575-581
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• 2007

As current and future automobile emission regulations become more stringent, the research on flow distribution for an exhaust manifold and close-coupled catalyst(CCC) has become an interesting and remarkable subjects. The design of a CCC and exhaust manifold is a formidable task due to the complexity of the flow distribution caused by the pulsating flows from piston motion and engine combustion. Transient flow at the exhaust manifold can be analyzed with various computational fluid dynamics(CFD) tools. However, the results of such simulations must be verified with appropriate experimental data from real engine operating condition. In this study, an experimental approach was performed to investigate the flow distribution of exhaust gases for conventional cast types and stainless steel bending types of a four-cylinder engine. The pressure distribution of each exhaust sub-component was measured using a simulated dynamic flow bench and five-hole pitot probe. Moreover, using the results of the pitot tube measurement at the exit of the CCC, the flow distribution for two types of manifolds(cast type and bending type) was compared in terms of flow uniformity. Based on these experimental techniques, this study can be highly applicable to the design and optimization of exhaust for the better use of catalytic converters to meet the PZEV emission regulation.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.121-124
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• 2006

The arteries are very important in cardiovascular system and easily adapt to varying flow and pressure conditions by enlarging or shrinking to meet the given hemodynamic demands. The blood flow in arteries is dominated by unsteady flow phenomena due to heart beating. In certain circumstances, however, unusual hemodynamic conditions cause an abnormal biological response and often induce circulatory diseases such as atherosclerosis, thrombosis and inflammation. Therefore quantitative analysis of the unsteady pulsatile flow characteristics in the arterial blood vessels plays important roles in diagnosing these circulatory diseases. In order to verify the hemodynamic characteristics, in-vivo measurements of blood flow inside the extraembryonic arterial bifurcation cascade of chicken embryo were carried out using a micro-PIV technique. To analyze the unsteady pulsatile flow temporally, the (low images of RBCs were obtained using a high-speed CMOS camera at 250fps with a spatial resolution of $30{\mu}m\times30{\mu}m$ in the whole blood vessels. In this study, the unusual flow conditions such as flow separation or secondary flow were not observed in the arterial bifurcations. However, the vorticity has large values in the inner side of curvature of vessels. In addition, the mean velocity in the arterial blood vessel was decreased and pulsating frequency obtained by FFT analysis of velocity data extracted in front of the each bifurcation was also decreased as the bifurcation cascaded.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.183-190
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• 2009

The objective of this study is to get simulation data about pulsatile flow around an interior solid body inside a bifurcated tube. All the processes were based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. The bifurcated tube models were drawn with the bifurcated angle of 45 degrees, considering Murray's law about the diameter ratio. With various locations of the object, the effects of flow on the drag were considered. For the pulsating flow condition, the velocity wave profile was given as the inlet boundary condition. To validate all the result, the simulation was compared with the existing data of the other papers first. Overall flow field of both data were similar, but there was some difference at a zero velocity. Therefore the next simulation was continued with the sine wave profiles where there is no negative flow, and then the data was compared with one of the pulmonary artery velocity where there is negative flow. The final process was to calculate flow variables such as the wall shear stress (WSS) and to compute the drag of the solid object.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.923-930
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• 2012

The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.

• Journal of Power System Engineering
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• v.12 no.1
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• pp.13-19
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• 2008

In this study, a variable induction and exhaust system is applied to turbocharged diesel engine to improve the volumetric efficiency, especially, in a low and transient engine speed range where much of the pollutant matters are expelled out. The volumetric efficiency is known as one of the most important factor which affects significantly engine performance, fuel economy and further emission and noise level. As the torque increase with the engine speed up, the gas flow in an exhaust pipe become pulsating and then has an effect on boost up capacity of air charging into the cylinder and expelling capacity to atmosphere simultaneously. But at a low and idling speed, the pulsation effect was not so significant. Accordingly, resonator was employed to compensate their loss. The variable induction system consists of the secondary pipe, resonator, intercooler, and torque variance were examined with extended operating conditions. In the mean time, for interpretation and well understanding for the phenomena of wave action that arising during intake and exhaust process between turbocharger and variable intake system, the concept of the combined supercharging was introduced. Some of results are depicted which deal with a pressure history during valve events of induction process. Consequently, by the governing of these phase and amplitude of pulsating wave, it enables us to estimate and evaluate for the intake system performance and also, designing stage of the system layout.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.817-818
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• 2010

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.2
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• pp.196-201
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• 2012

This study represents numerical study on the thermal and fluid flow characteristics of exhaust gas in a motorcycle muffler. The engine generates 125cc of displacement. Numerical analysis with computational fluid dynamics(CFD) was carried out to investigate the exhaust gas that flow into a motorcycle muffler. The STAR-CD S/W used to analyze three dimensional steady state and transient in a muffler. The Navier-Stokes Equation is solved with SAMPLE and PISO method in cartesian coordinates system. As the numerical result, it could be confirmed pulsating pressure generated from inlet of muffler become closer to the atmospheric pressure through baffle. Also the numerical result was almost identical to experimental result and, through the comparison, the reliability of numerical result was confirmed.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.538-541
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• 2008

This study considers the feasibility of the concentration control of the feul and air by oscillating flow in the channel of Fuel Cells. Fuel Cell Stack performance is largely influenced by the fuel and air concentration. If the fuel and air concentration is lower than stoichiometry 1.25 of the fuel and 2.5 of the air, its performance deteriorates seriously because of the fuel and air starvation. In this respect the optimization of the fuel and air concentration is crucially important to maximize fuel cell stack performance. In this work, the effects of oscillating actuation are studied to control the concentration. Two important nondimensional parameters are introduced, each of which represents either the oscillating frequency or the oscillating amplitude. It is shown how these factors affect the stack performance and the efficiency of the fuel cell stack stack.

• Journal of Energy Engineering
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• v.24 no.2
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• pp.115-119
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• 2015

Pipe vibration caused great threat to the safety in production. Strong pipeline vibration will line accessories, especially the joints and pipe fittings etc. pipe joints loosening and rupture, causing serious accidents. By the action of the compressor constant fluid flow within the pipe, this process produces pulsating fluid flow may cause vibration of the pipe, thereby reducing the efficiency of the pipeline, structural vibration induced fatigue, thereby resulting in even piping structural damage. This paper studies on the vibration problems caused by fluid, by analyzing the causes of pipeline vibration and factors affecting pipeline vibrations, FEM (Finite Element Method) analysis of modal and enforced vibration.