Kwanjung Yee

Helicopter Rotor Shape Optimization for the Improvement of Aeroacoustic Performance in Hover

A helicopter rotor is optimally designed for aeroacoustic performance improvement. As shown in previous reports, the blade shapes can be designed to minimize high-speed impulsive noise but tend to have excessively high tapers and be swept back. Since an overly short chord length around the blade-tip region may cause structural problems and safety issues in autorotation, an autorotation index has been introduced to keep the tip region from having excessive taper ratios. In addition, the changes in thickness and camber of the airfoils can also be taken into account to better represent realistic rotor shapes. Aeroacoustic analysis is performed using Kirchhoffs method coupled with computational fluid dynamics analysis, and the optimization is performed using the kriging-model-based genetic algorithm method. Optimization results are presented that show that the designed blades have improved aerodynamic performance and reduced high-speed impulsive noise characteristics. It is found that a more practical blade shape can be obtained by using airfoil transitions and an autorotation index. The results of the analysis of variance and self-organization map indicate that the taper ratios, the swept back, the tip chord length, the protrusion shape, the camber, and the thickness of the root airfoil are the prominent features affecting the aeroacoustic performance of the rotor.

Verification of the Open Source Code, OpenFOAM to the External Flows

This paper aims to verify the applicability of OpenFOAM, the widely recognized open source CFD code, to external flows commonly found in aeronautical problems. To this end, several representative flow cases are selected first from subsonic to supersonic flow fields. Then, the computational results obtained from OpenFOAM are systematically compared against available data from experiments and other numerical codes. It was found that the strength and location of shock are well predicted and the effects of boundary conditions on the computed results are reviewed. Subsonic flow with massive separation is selected to validate the prediction capability of OpenFOAM. Based on the current results, the limitation and possibility of OpenFOAM was confirmed and for future study using OpenFOAM was suggested.

Parametric Study for Hovering Performance of a Coaxial Rotor Unmanned Aerial Vehicle

This paper proposes a reliable aerodynamics analysis method designed for a coaxial rotor unmanned aerial vehicle. It is then used to investigate the effects of the selected design parameters on the hovering performance of the coaxial rotor. A coaxial rotor performance analysis code based on the source-doublet panel method is developed, and its accuracy is verified to be sufficient by comparing its results to various test data. Through a parametric study for the rotor design parameters, such as radius, twist, and taper, the effect of each parameter on the coaxial rotor design is investigated and a statistical analysis for the resulting data is conducted. The results show that the diameter has the biggest impact on the hovering performance of a coaxial rotor, whereas the taper has the biggest impact if the diameter is fixed. Based on these findings, a revised rotor platform is proposed, with 33 % improvement of the figure of merit over the baseline concept, which implies that the optimal design significantly improves the performance of the rotor under development.

Optimization of the Array of Film-Cooling Holes on a High-Pressure Turbine Nozzle

A high-fidelity yet affordable design procedure is proposed for a film-cooling hole array optimization and subsequently applied to the array on the nozzle pressure side of the high-pressure turbine. To make this possible, the efficient array shape parameterization method combined with the efficient global optimization method is introduced. As a result of optimization, the average and variation of the wall temperature are reduced by approximately 10 and 25%, respectively. Also, it is confirmed from the results that the superior cooling performance is obtained when the array has smaller hole distances at the hub rather than at the shroud and when the array is disposed on the upstream position rather than on the downstream position. Finally, it is concluded that the performance improvement due to the optimized hole array amounts to the equivalent effects of increasing cooling air by 1.66% of the main passage mass flow.

Robust Design Optimization of Unmanned Aerial Vehicle Coaxial Rotor Considering Operational Uncertainty

This research aims at performing robust design optimization by taking into account operational uncertainties to improve the performance of the coaxial rotor unmanned aerial vehicle that is under development. For this sake, neural networkmodels are constructed for aerodynamic performance obtained from a source-doublet panelmethod coupled with a time-marching free wake method. Two kinds of operational uncertainties are considered: ballistic damage on blades and weight variation due to the mission change. Approximate moment approach is employed to evaluate the robustness of performance. Subsequently, a relationship between the robustness of performance indices and the parameters representing blade geometry is investigated. In addition, the robustness of the performance indices and constraints for three different solutions chosen from the Pareto optima set is studied. It is confirmed that the trend of design variables to improve performance is in contradiction to the robustness of design. Besides, by incorporating the robust design method, a probability for a designed coaxial rotor to accomplish missions successfully can be improved by 70 95% under the uncertainty of ballistic damage.

Development of an Aerodynamic Performance Analysis Module for Rotorcraft Comprehensive Analysis Code

In this study, an aerodynamic performance analysis code has been developed as a part of rotorcraft comprehensive program. Airloads on rotor blades are calculated based on the blade element theory with look-up tables of aerodynamic coefficients of 2-D airfoils. In order to calculate rotor induced inflow, various inflow prediction methods such as linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot`s inflow distribution and sectional normal force coefficients of AH-1G.

Numerical Investigation on Overlap Effects of Tandem Rotors in Forward Flight

A study on the interference effects of overlapping tandem rotors in forward flight is conducted using the time-marching free-wake panel method which adopts field velocity boundary integral formulation. The conventional boundary integral formulation is numerically unstable for the cases when the blade and the wake are in close proximity to each other. In order to avoid this problem, this study applies the field velocity method and modifies the boundary integration formulation. The improved method is used for the parametric study on the advance ratio and the distance between the rotors. These are the parameters that most affect the interference of the tandem rotor in forward flight. Comparison of the aerodynamic performance shows that the horizontal distance between the rotors negligibly influences the overlap-induced power factor for high advance ratio. In addition, it shows that the overlap-induced power factor is inversely proportional to the squared vertical distance between the rotors, and that the overlap-induced power factor increases to a certain extent and decrease back as the advance ratio increases.

High-to-Low Initial Sample Ratio of Hierarchical Kriging for Film Hole Array Optimization

This study aims at proving the existence of the optimal number of high initial sample for time-efficient optimization and demonstrating that the reliable optimization results can be guaranteed when...

Optimum Arrangement of Film Cooling Holes Considering the Manufacturing Tolerance

Despite several studies on the optimum shape of film cooling holes, only a small number of research efforts have attempted to optimize the hole arrangement for film cooling. Moreover, although the ...

Ice Accretion on Helicopter Fuselage Considering Rotor-Wake Effects

To accurately predict the ice shape on the fuselage under rotor-wake effects, discrete modeling of individual tip vortices is essential to determine the local aerodynamic interactions between the vortex and the fuselage. To this end, the actuator surface model is developed and applied to the present study. Then, water-droplet-trajectory prediction, thermal analysis, and ice growth module are seamlessly integrated. This study aims to perform detailed analysis of the rotor downwash effects on ice that accretes on a helicopter fuselage and to determine the variation with respect to the forward flight speed. As a result of comprehensive numerical computations, the following conclusions are reached. First, the rotor inflow transforms the droplet trajectories, the location of ice accretion and the amount of ice are changed. Actually, 16.5% less ice is accumulated on the overall fuselage in the rotor–fuselage interaction case compared to the isolated fuselage case. Second, a clear-cut distinction of the icing lo...