Jang-Sik Yang

Study of thermal phenomena in the cabin of a passenger vehicle using finite element analysis: human comfort and system performance

A numerical simulation is performed to evaluate the thermal comfort of passengers and the performance of a defroster. In this study, a grid system based on a real vehicle and a finite element human model are used with an appropriate time step. The turbulent nature of the flow is modelled using a standard k–ε model according to the logarithmic law of the wall. The complex flow characteristics inside the passenger compartment are shown with simultaneous velocity and temperature fields in several sections of the flow domain. Through a predicted mean vote analysis, the thermal comfort of the passengers is discussed, in particular with respect to the measured location of the seat and the measured position of the passenger. An additional study is conducted on the defrost mode with respect to the defrosting performance which is closely related to passenger safety. The velocity profile at the defrost nozzle is interpolated to the inlet boundary surface node through a defrost duct simulation. The monitored points on the ice boundary indicate the melting time, the phase-change duration, the change in the enthalpy and other useful information.

A study on Flow Characteristic inside Passenger`s Compartment under Recirculation Cool vent mode using CFX

The flow characteristics under recirculation cool vent mode is numerically studied using commercial fluid dynamic code(CFX). For the reliable analysis, real vehicle and human FE model is employed in grid generation process. The geometrical location and shape of panel vent, and exhaust vent is set as that of real vehicle model. The flowrate of the working fluid is determined as 330CMH which is equivalent to 70 percent of maximum capacity of HVAC system. The high velocity regions are formed around 4 each panel vent. Because of the non-symmetrically located exhaust, non-uniform flow and partial backflow near the door trim is observed. Streaklines start from each panel vent show the flow pattern of the airflow in the passenger`s compartment very well.

Observation of Oil Flow Characteristics in Rolling Piston Rotary Compressor for Reducing Oil Circulation Rate

The oil circulation rate (OCR) of the rolling piston rotary compressor is a significant factor which affects the performance of refrigeration system. The increase of oil discharge causes decreasing of the heat transfer efficiency in the heat exchanger, pressure drop and lack of oil in lubricate part in compressor. In this study, the internal flow of compressor was visualized to figure out the oil droplet flow characteristics. The experiments and Computational Fluid Dynamics (CFD) simulations were conducted in various frequency of compressor to observe the effect of operation frequency on oil droplet flow characteristics for reducing OCR. In situ, measurement of oil droplet diameter and velocity were conducted by using high speed image visualization and Particle Image Velocimetry (PIV). The flow paths were dominated by copper wire parts driving the motor which was inserted in compressor. In order to verify the reliability of CFD simulation, the tendency of oil flow characteristics in each flow path and the compressor operating conditions were applied in CFD simulation. For reducing OCR, the structure such as vane, disk and ring is installed in the compressor to restrict the main flow path of oil particle. The effect of additional structure for reducing OCR was evaluated using CFD simulation and the results were discussed in detail.

The natural convection in a three dimensional enclosure using color capturing technique and computation

The natural convection of a horizontal layer heated from below in a three-dimensional rectangular enclosure was dealt with both numerically and experimentally. The aspect ratios are 1:2:3.5 and Boussinesq fluid is water with the Prandtl number of 5.0. This experimental study showed how to measure the variation of temperature field in a 3-D rectangular enclosure with small aspect ratios by using TLC(Thermochromic Liquid Crystal) and color capturing technique. The experimental temperature field had periodic characteristics of 75 sec at Ra=2.37*10 . But the numerical convection flow had periodic characteristics of 79 sec at the same Rayleigh number. In three dimensional computation it was found that the convection roll structure bifurcated from four rolls to two rolls as the Rayleigh number is increased.

Study on the Performance of a Centrifugal Compressor Using Fluid-Structure Interaction Method

Abstract : In this study, we perform a series of aero-thermo-mechanical analyses to predict the running-tip clearance and the effects of impeller deformation on the performance using a centrifugal compressor. During operation, the impeller deformation due to a combination of the centrifugal force, aerodynamic pressure and the thermal load results in a non-uniform tip clearance profile. For the prediction, we employ the one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The predicted running tip clearance shows a non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height occurred at the leading and trailing edges of the impeller. Because of the reduction of the tip clearance, the tip leakage flow decreased by 19.4％. In addition, the polytrophic efficiency under operating conditions increased by 0.72％. These findings confirm that the prediction of the running tip clearance and its impact on compressor performance is an important area that requires further investigation.

Analytical Study on the Performance of Centrifugal Compressor Considering Running Tip Clearance

In this study, a series of aero-thermo-mechanical analyses were carried out to predict the running tip clearance and the effects of impeller deformation on the performance using two different centrifugal compressors (blade type A and B). In operation, impeller deformation due to the combination of centrifugal force, aerodynamic pressure and thermal load results in non-uniform tip clearance profile. The predicted running tip clearance leads to further findings of its impact on compressor performance. The prediction employs one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The results show that the maximum displacement occurs at the leading edge tip of the impeller blade but maximum stress takes place at the blade root of the impeller for these particular designs. The analysis also confirms the centrifugal force has dominant effect on impeller deformation at its operating condition. The predicted running tip clearance shows non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height has occurred at the leading edge and the trailing edge of the impeller. Due to the reduction of the tip clearance, the tip leakage flow has decreased by 19.4% and 16.2% in the blade type A and B, respectively. Also, the polytropic efficiency of the blade type A and B at operating condition has increased by 0.72% and 1.81%, respectively. These findings confirm that the prediction of running tip clearance and its impact on compressor performance is important area for further investigation.© 2015 ASME

Detailed Measurement of Flow and Heat Transfer Downstream of Rectanglar Vortex Generators Using a Transient Liquid Crystal Technique

The effects of the interaction between flow field and heat transfer caused by the longitudinal vortices are experimentally investigated using a five hole probe and a transient liquid crystal technique. The test facility consists of a wind tunnel with vortex generators protruding from a bottom surface and a mesh heater. In order to control the strength of the longitudinal vortices, the angle of attack of vortex generators used in the present experiment is 20, and the spacing between the vortex generators is 25mm. The height and cord length of the vortex generator is 20mm and 50mm, respectively. Three-component mean velocity measurements are made using a f-hole probe system, and the surface temperature distribution is measured by the hue capturing method using a transient liquid crystal technique. The transient liquid crystal technique in measuring heat transfer has become one of the most effective ways in determining the full surface distributions of heat transfer coefficients. The key point of this technique is to convert the inlet flow temperature into an exponential temperature profile using the mesh heater set up in the wind tunnel. The conclusions obtained in the present experiment are as follows: The two maximum heat transfer values exist over the whole domain, and as the longitudinal vortices move to the farther downstream region, these peak values show the decreasing trends. These trends are also observed in the experimental results of other researchers to have used the uniform heat flux method.

The Experimental Study of the Interaction Between the Flow rind Temperature Field and a Boundary Layer Due to a Variety of tole Height of a Vortex Generator

The effects of the interaction between the flow and temperature field and a boundary layer due to a variety of the height of a vortex generator are experimentally investigated. The test facility consists of a boundary-layer wind tunnel with the vortex generator protruding from the bottom surface. In order to control the strength of the longitudinal vortices, the angle of attack and the spacing distance of the vortex generator are 20 degree and 40 mm, respectively. The height of the vortex generator (H) is 15 mm, 20 mm and 30 mm and the cord length of it is 50 mm. Three-component mean velocity measurements are made using a 5-hole probe system and the surface temperature distribution is measured by the hue capturing method using thermochromatic liquid crystals. By using the method mentioned above, the following conclusions are obtained from the present experiment. The boundary layer is thinned in the downwash region where the strong downflow and the lateral outflow of the boundary layer fluid occur and thickened in the upwash re,3ion where the longitudinal vortex sweeps low momentum fluid away from the bottom surface. In case that the height of the vortex generator increases, the averaged circulation and the maximum vorticity of the vortex pair decrease. The contours of the non-dimensional temperature show the similar trends fur all the cases (H

A Numerical Simulation of Longitudinal Vortex in Turbulent Boundary Layers

This paper represents numerical computations of the interaction between the longitudinal vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of longitudinal vortices introduced in turbulent boundary layers. The flow field behind vortex generator is modeled by the information that is available from studies on the delta winglet. Also, the Reynolds-averaged Navier-Stoke equations for three-dimensional turbulent flows, together with a two-layer turbulence model to resolve the near-wall flow, is solved by the method of pseudo compressibility. The present results show that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall, and have a good agreement with the experimental data

An Experimental Study on the Effects of the Boundary Layer and Heat Transfer by Vortex Interactions ( I ) - On the common flow down -

The flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices were studied experimentally. The test facility consisted of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta wings protruding from the surface. In order to control the strength of the longitudinal vortices, the angles of attack of the vortex generators were varied from - 20 degree to - 45 degree, but spacings between the vortex generators were fixed to 4 cm. The 3-dimensional mean velocity measurements were made using a five-hole pressure probe. Heat transfer measurements were made using the thermochromatic liquid to provide the local distribution of the heat transfer coefficient. Unlike common flow down, common flow up vortices moved toward the centerline as they developed and interacted strongly with each other but not with the boundary layer. Spanwise profiles of Stanton number were similar for , but not similar for . The case of showed the two peak Stanton number, but the case of showed the only one peak Stanton number.