Myungsung Lee

A Numerical Study on the Effect of Mountainous Terrain and Turbine Arrangement on the Performance of Wind Power Generation

A three-dimensional flow simulation was performed to investigate the flow field in a wind farm on a complex terrain. The present study aims to examine the effects of mountainous terrain and turbine arrangement on the performance of wind power generation. A total of 49 wind turbines was modeled in the computational domain; detailed blade shape of the turbines was considered. Frozen rotor method was used to simulate the rotating operation. The torque acting on the turbine blades was calculated to evaluate the performance of the wind turbines. The numerical results showed details of the flow structure in the wind farm including the velocity deficit in the separated flow regions; this velocity deficit was due to the topographical effect. The effect of the wake induced by the upstream turbine on the performance of the downstream wind turbine could also be observed from the results. The methodology of the present study can be used for selecting future wind-farm sites and wind-turbine locations in a selected site to ensure maximum power generation.

A DETAILED CFD SIMULATION OF THE 2003 DAEGU METRO STATION FIRE

The Daegu metro station fire on 18 February 2003 was a tragic accident that claimed 192 lives in South Korea. The fire was set by an arsonist in a stopped train at the Daegu metro station, and spread to another train arriving at the station on the opposite track. The present numerical study aims to reproduce the Daegu metro station fire using a transient 3-D CFD simulation with detailed geometry of the station and tunnels in order to understand the behavior of the smoke and heat responsible for human losses in such accidents. The actual motion of the arriving train was also considered by using a moving mesh technique, and the fire development and CO gas generation were modeled with the enthalpy and scalar source terms. The evolutions of the temperature and CO gas distributions in the station were obtained in detail from the present simulation. The heat and CO concentrations at some critical locations (such as staircases) were shown and discussed in detail. The results of the present numerical study could provide useful data for future emergency plans of metro stations in case of fire.

Numerical analysis of heat transfer in a plate heat exchanger

In the present study, a numerical methodology of the heat transfer analysis of a plate heat exchanger is investigated. An analysis method for the conjugate heat transfer between the repeating set of a cold flow passage, separating plates, and a hot flow passage of a plate heat exchanger is proposed and successfully performed by using the periodic boundary condition at the center area of the plate and appropriate inlet and outlet conditions for the two streams. Comparison of the heat transfer results of the proposed analysis method with the available experimental data showed a good agreement.

Correlation between intravesical pressure and prostatic obstruction grade using computational fluid dynamics in benign prostatic hyperplasia

An urodynamic test which measures various physiologic variables during voiding is generally used for accurate diagnosis of a bladder outlet obstruction (BOO) resulting from benign prostatic hyperplasia (BHP). However, this method is difficult to directly apply to all patients because it is an invasive test and many patients suffer from anxiety and embarrassment during the test. Thus, other diagnosis methods such as uroflowmetry and prostatic symptom score are performed to measure the degree of BOO prior to the urodynamic test, and it is necessary to construct a quantitative relationship among the obstruction level, the intravesical pressure, and the uroflow rate. The aim of this paper is to analyse the variation of intravesical pressure as a function of the extent of the obstruction and the uroflow rate from given information on the size of the bladder and the urodynamic test using a computational fluid dynamics approach. In order to analyse the intravesical pressure, a two-dimensional axisymmetric model of the bladder including a narrowed region, i.e. the prostatic obstruction, is created. Then the variation of the intravesical pressure is quantitatively obtained as a function of the magnitude of the uroflow rate and the extent of the obstruction. It is shown that the intravesical pressure significantly increases even for small obstructions and that at large obstructions it can reach values higher than 100 cm H20, which is a dangerous value. It is shown that the intravesical pressure decreases as the uroflow rate decreases. This study can form the basis of a non-invasive test for the diagnosis of BHP.

NUMERICAL SIMULATION OF VENTILATION IN THE STORAGE HALLS OF TRIPITAKA KOREANA AT HAEINSA TEMPLE IN CASE OF BUILDING REARRANGEMENT

In the present study, ventilation flow in the Janggyeongpan-Jeon at Haein temple in case of building rearrangement has been investigated numerically. To achieve more accurate results, detailed shapes such as buildings and the window grills are modeled and tree canopy model is adopted to account for the effect of trees in the computation. Wind velocities as boundary condition are taken from meteorological statistical data. The numerical results show that ventilation flow distributions at Janggyeongpan-Jeon in case of building rearrangement are nearly similar to those before rearrangement.

A Numerical Study on Flow and Heat Transfer Analysis of Various Heat Exchangers

This paper describes numerical methodologies of the flow and heat transfer analysis in heat exchangers of various types. Heat exchangers considered in the present study include a louver fin radiator for a vehicle, a shell and tube heat exchanger for HVAC and plate heat exchangers with patterns of herringbone and of dimple used in waste heat recovery. For the analysis of the louver fin radiator, a 3-D Semi-microscopic Heat Exchange (SHE) method was used. SHE was characterized by conjugated heat transfer analysis for the domain which consists of water in a tube, tube wall, the region where passes through the louver fin and ambient air. It is shown that both the air flow in louver fin area and the water flow inside the cooling water passages are successfully predicted along with the heat transfer characteristics. A conjugate heat transfer analysis in a shell and tube heat exchanger was also performed. For the analysis of entire shell side of the heat exchanger, geometric features such as tubes, baffles, inlet and outlet were modeled in detail. It is shown from the analysis that a design modification for better flow distribution and thus for better performance can be proposed. Finally an analysis method for the conjugate heat transfer between hot flow–separating plate–cold flow of a plate heat exchanger was proposed. By using periodic boundary conditions for the repeating sections and appropriate inlet and outlet boundary conditions, the heat transfer in a plate heat exchanger with patterns of herringbone and of dimple was successfully analyzed. Comparisons of the present numerical results are in a good agreement with available experiment data.

Heat Transfer Augmentation in a Divergent Duct with Angled Ribs

Heat transfer characteristics in the rectangular divergent duct with parallel angled ribs are experimentally compared with the straight smooth circular duct. The ribs with four different parallel angles (α=30∘, 45∘, 60∘, and 90∘) are glued on the duct’s two opposite walls as well as on the duct’s one sided wall only, respectively. The 0.72∘-inclined walls are installed at the two opposite walls of the rectangular divergent duct. The test section of 1000mm long has the cross section of 100×75mm2 at inlet and 100×100mm2 at exit. The ribbed walls are manufactured with a rib height (e)=10mm and the ratio of rib spacing (p) to height(e) = 10. The main findings are summarized that the increase in the dimensionless Nusselt number for the flow attack angles can be seen in the order of 90∘, 30∘, 60∘, and 45∘ at the two opposite ribbed divergent wall ducts, in addition, the average Nusselt number in the divergent rectangular duct with two opposite ribbed walls is somewhat greater than in the ribbed straight cross-sectional rectangular duct.