Chun-Taek Kim

Power Characteristic Variation Simulation of Hybrid Electric Propulsion System for Small UAV

It is conducted that power characteristic variation simulation of electric propulsion system that uses fuel cells, solar cells and a battery as power sources. Combining each power source, 400W electric propulsion system have been modeled and verified. In result, without active control logic, it is confirmed that battery`s power response is faster than other power sources at starting and transient condition, fuel cell and solar cell are a major electrical power during cruise condition. After completing flight, SOC is 24.2% at the winter solstice and is 93% at the summer solstice, It is revealed that active power control for sustaining proper SOC is necessary as a securing the system safety and effective power distribution.

Uncertainty Assessment Using Monte Carlo Simulation in Gas Flow Measurement

Monte Carlo simulation(MC) method was used as an uncertainty assessment tool for gas flow measurement in this paper. Uncertainty sources for gas flow measurement were analyzed, and probability distribution characteristics of each source were discussed. Detailed MC methodology was described including the effect of the number of simulation. The uncertainty result was compared with that of the conventional sensitivity coefficient method, and it was revealed that the results were different from each other for this particular gas flow measurement case of which the modelling equation was nonlinear. The MC was comparatively simple, convenient and accurate as an uncertainty assessment method, especially in cases of complex, nonlinear measurement modelling equations. It was noted that the uncertainty assessment method should be selected carefully according to the mathematical characteristics of the measurement.

Aerodynamic Optimization of Axial Turbine Tip Cavity With Approximation Model

Design optimization of unshrouded rotor tip cavity of a high pressure turbine stage with low aspect ratio was carried out to maximize the turbine stage efficiency. Cavity shapes were parameterized with 4 design variables including rim thickness, cavity depth, cavity front blend radius and cavity aft blend radius. Initially the CCD method was utilized for sampling experimental points and the Kriging method was chosen to construct an approximation model. The optimum points derived from the approximation model were assessed by CFD analyses to verify the approximation model. The approximation model was refined repeatedly by adding more experiment points to minimize difference of CFD result and predicted value from the approximation model at the optimum point.The optimization result showed that there is an optimum ratio of cavity depth to tip clearance height, while the optimum design suggests cavity front blend radius and cavity aft blend radius be as small as possible within the design range. As the tip clearance height increases, the optimized tip cavity depth increases. However, the rim thickness has little effect on the optimum tip cavity depth. Without the tip cavity, leakage flow at fore part of the blade suction surface develops large vortex flow from the starting point of the unguided turning region due to adverse pressure gradient. The tip cavity prevents the early leakage flow from flow to the suction surface, which suppresses the leakage flow dissipation to the loss. It results in efficiency improvement. The effect of the tip cavity on the efficiency increases at the larger tip clearance.On the other hand, the cavity rim thickness effect on the efficiency becomes noticeable when the tip cavity depth is over than the optimum value. The rim thickness effect mainly appears on the tip leakage flow after the blade throat. The leaked flow after the blade throat generates a high loss region near the blade tip, especially when the rim thickness is small. The loss from the thick tip cavity rim gradually increases as the tip clearance increases. However, the rim thickness effect is most sensitive when the tip clearance is small. The loss generation mechanism due to the rim thickness is totally different to the tip cavity depth effects on the total pressure loss.Copyright

Surge Line Measurement of a Gas Turbine Engine by Fuel Spiking Test

A fuel spiking test was performed to find out a surge line of the compressor in a gas turbine engine. During the test, fuel spiking signal was superposed on the engine controller demand signal and the mixed signal was used in controlling a fuel control valve. For the superposition, a subsystem composed of a fuel controller and a function generator was used. During the fuel spiking test, the original fuel signals and the modified signals were compared to guarantee the consistency excluding the fuel spiking signals. The fuel spiking signal was carefully selected to keep the engine speed constant. The fuel spiking effect was checked by three dynamic pressure sensors. Sensors were placed at the front of the fuel control valve, at the rear of the fuel control valve, and at the compressor discharge location, respectively. Also, three accelerometers were set up on the outer casing of the compressor part to measure the vibration of the engine during the fuel spiking. In the engine test, the effect of the fuel spiking signals modulated by spiking time and amplitude were examined in order to move the operating point up to the surge region without any change of the engine speed. The real engine test was performed at the Altitude Engine Test Facility (AETF) in Korea Aerospace Research Institute (KARI). In the preliminary test, the fuel spiking signals are in good agreement with the dynamic pressure of the fuel flow. The compressor discharge pressure also shows the fuel spiking effects as expected at the compressor. After the preliminary test, fuel spiking signals with 12.5~50ms in time and 84~505% in excessive fuel flow were applied to find out a surge point at specific engine speed. The test result shows that the fuel spiking is a very effective method to make surge. This experimental data could give actual surge line information of a real engine.

Improving the Measurement Uncertainty of Altitude Test Facility for Gas Turbine Engines

An Altitude Engine Test Facility(AETF) was built at the Korea Aerospace Research Institute in October 1999 and has been being operated for altitude testing of gas turbine engines of 3,000 Ibf class or less. The AETF has been calibrated using several engines such as J69 of Teledyne Co. as a facility checkout engine. Uncertainty analyses on the air flow rate and thrust were performed using the test results, according to ASME PTC 19.1-1998. Several modifications on the facility and test method were made in order to improve the measurement uncertainty to a satisfactory level over the whole operating envelop. Spatial distributions of pressure and temperature were measured, sensors were substituted by more accurate ones, inlet duct was modified to refine the flow quality, and pressure control logic was revised to remove the cell pressure fluctuation. As a result, the uncertainty of the air flow measurement was improved by 0.1% over all the test conditions, and the net thrust measurement by up to 3%. The improved measurement uncertainties of air flow and thrust are 0.68～O.73% and 0.4～1.3%, respectively.

Small Turbojet Engine Test and Uncertainty Analysis

The Altitude Engine Test Facility(AETF) was built at the Korea Aerospace Research Institute and has been being operated for the gas turbine engines in the class of 3,000 lbf thrust. To enhance the confidence level of AETF to the international level, a series of studies and facility modification have been conducted to improve the measurement uncertainty and reliability. In this paper, some part of the facility evaluation tests performed with a single spool turbojet engine are introduced. Tests were performed simulating the flight conditions as steady state, sea level for various flight speeds (i.e., Mn

Experimental Research on the Altitude Performance of an Auxiliary Power Unit for Helicopters

An APU(Auxiliary Power Unit) for helicopters has been developed in Korea and tested at the AETF(altitude engine test facility) in KARI(Korea Aerospace Research Institute) for the purpose of the military qualification. A cell correlation test was performed before the official test, and the results are within the tolerance. The APU has the capability of supplying electric power as well as compressed air to the helicopters. It was tested at bleed extraction conditions, electric power extraction conditions, and maximum continuous concurrent power conditions within the entire helicopter flight envelop. Some special test equipments were implemented for the measurement of air flowrate, electric power and so on. The tests were successfully performed and their results satisfy the requirements of the helicopters.

Prediction of Gas Turbine Engine Steady Performance from Transient Performance Test

Methodology of predicting steady performance of gas turbine engine from transient test data was explored to develop an economic performance test technique. Discrepancy of transient performance from steady performance was categorized as dynamic, thermal and aerodynamic transient effects. Each effect was mathematically modeled and quantified to provide correction factors for calculating steady performance. Engine performance tests were conducted at Altitude Engine Test Facility of KARI. The influence of engine inlet/outlet condition change on engine performance was corrected firstly, and then steady performance was predicted from the correction factors. The result was compared with steady performance test data. This correction method showed an acceptable level of precision, 3.68% difference of fuel flow.