Kwanjung Yee

Kwanjung Yee
Seoul National University | SNU · Department of Mechanical Aerospace Engineering

Ph.D

About

148
Publications
8,725
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
553
Citations
Introduction
Kwanjung Yee currently works at the Department of Mechanical Aerospace Engineering, Seoul National University. Their most recent publication is 'Variable-Fidelity Optimization of Film-Cooling Hole Arrangements Considering Conjugate Heat Transfer'.

Publications

Publications (148)
Article
Autoencoder-based reduced-order modeling (ROM) has recently attracted significant attention, owing to its ability to capture underlying nonlinear features. However, two critical drawbacks severely undermine its scalability to various physical applications: entangled and therefore uninterpretable latent variables (LVs) and the blindfold determinatio...
Article
A novel spectrum calibration method is proposed for high-accuracy emission spectroscopy to extract quantitative gas property information from the spontaneous photon emission spectra. This is challenging, particularly in the presence of broadband emission, which smears the characteristic local spectral features that are often used as property indica...
Article
View Video Presentation: https://doi.org/10.2514/6.2022-3360.vid As the next-generation rotorcraft aims to achieve high-speed flight, the rotor blade structure inevitably experiences excessive vibratory loads. The hub vibration of the main rotor is one of the critical issues in modern rotorcraft that should be relieved through aeroelastic design of...
Preprint
Full-text available
Autoencoder-based reduced-order modeling has recently attracted significant attention , owing to the ability to capture underlying nonlinear features. However, its uninterpretable latent variables (LVs) severely undermine the applicability to various physical problems. This study proposes physics-aware reduced-order modeling using a β-variational a...
Article
This study examines the aerodynamic performances of a wing and multiple propellers through a parametric analysis of wing–propeller interactions. A flow analysis was conducted via simulations based on actuator disk method. The parameters analyzed included the number of propellers, rotating direction, and propeller interval. An increment in the numbe...
Article
Full-text available
Though inverse approach is computationally efficient in aerodynamic design as the desired target performance distribution is prespecified, it has some significant limitations that prevent full efficiency from being achieved. First, the iterative procedure should be repeated whenever the specified target distribution changes. Target distribution opt...
Article
Full-text available
Despite its various outdoor applications, the operation of quadrotors is restricted under strong winds due to their small size. Since the battery energy overconsumptions induced by the winds may lead to a mission failure, it is desirable to identify the tendency of excess battery energy and operable wind conditions according to ground speed, wind s...
Article
Full-text available
This technical comment is based on the previous work in AIAA Journal: Shu, L., Jiang, P., Song, X., and Zhou, Q., “Novel approach for selecting low-fidelity scale factor in multifidelity metamodeling,” AIAA Journal, Vol. 57, No. 12, 2019, pp. 5320–5330. doi: 10.2514/1.J057989. While reproducing their results, it was found that the hierarchical kri...
Article
Full-text available
Due to the instability of the pitching moment induced by the strong vortical flow at moderate to high angles of attack in the unmanned combat aerial vehicle (UCAV) configuration, previous design studies focused primarily on low-speed flight conditions where the longitudinal stability is a serious issue. Furthermore, because of the limitation of com...
Article
This paper focuses on the uncertainty propagation in the flight performance of multirotor-type unmanned aerial vehicles from the systematic perspective in conceptual design phase. The multirotor performance is estimated by a conceptual design and analysis framework which is capable of predicting the performance for given mission profiles and multir...
Article
The use of non‐intrusive reduced order modeling (NIROM) to approximate high‐fidelity computer models has been steadily increased over the past decade. Recently, local NIROM has been proposed to improve the model accuracy in highly nonlinear problems in which distinct characteristic regimes coexist. The core concept of local NIROM is the decompositi...
Article
A hybrid airfoil is a scaled model for generating a full-scale ice shape for icing wind tunnel tests. This is possible by matching full-scale properties such as the distributions of collection efficiency and heat transfer coefficient. Previous studies have used indirect methods using full-scale stagnation point location or tangent droplet trajector...
Article
This paper proposes a conceptual methodology for designing vertical takeoff and landing aircraft with a hybrid-electric propulsion system as an alternative to facilitate intercity missions for urban air mobility. Four new modules are developed to consider the diversity of configurations, flight mechanisms, and hybrid-electric propulsion system arch...
Article
The recent growing interest in urban air mobility (UAM) worldwide has led to the demand for physical analyses of the aerodynamic performance and aeroacoustic characteristics of electric vertical takeoff and landing (eVTOL) rotorcraft. In a UAM eVTOL rotorcraft, the smaller vortices generated from multiple propulsors interact with lifting surfaces s...
Article
Full-text available
To ensure safe flight in icing conditions it is essential to understand ice accretion, its effect on aerodynamic performance and ice shedding in any aircraft certification program. Ice fragments shed from a rotorcraft windshield and other locations can be detrimental if they are ingested into the engine intake or impinge on the tail rotor. Because...
Preprint
Full-text available
Though inverse approach is computationally efficient in aerodynamic design as the desired target performance distribution is specified, it has some significant limitations that prevent full efficiency from being achieved. First, the iterative procedure should be repeated whenever the specified target distribution changes. Target distribution optimi...
Article
Full-text available
Large droplet dynamics, such as droplet–wall interactions and droplet breakup, have a significant impact on the icing process, under super-cooled large droplet (SLD) conditions. Accordingly, many studies have been conducted to numerically implement the effects of large droplet dynamics on the 2nd generation icing codes. Most of them have focused pa...
Article
In recent years, the technical advancement of electric propulsion systems has contributed to the growing applicability of multirotor-type unmanned aerial vehicles from personal hobbies to industrial fields. Industrial fields involve various mission profiles comprising several mission-legs, such as hover and forward flight. Thus, enhancing the appli...
Article
Appropriately modeling surface roughness is crucial for predicting in-flight icing due to its influence on convective heat transfer. Most prevalent numerical simulations to this end rely on empirical correlations, where surface roughness is assigned a constant value. This limits the accurate computation of turbulent transitions, leading to a discre...
Chapter
Since inflight icing severely threatens the operational safety, it is crucial to accurately predict the ice accretion and resulting performance degradation for the design of anti‐/de‐icing devices. Both experimental and numerical approaches are used to investigate inflight icing phenomenon, however due to cost and time efficiency, the numerical sim...
Article
In glaze ice conditions, beads on the surface usually grow to form roughness elements through coalescence, finally resulting in enhancement of local collection efficiency. However, the effects of roughness elements due to freezing of beads are not reflected on the local collection efficiency in CFD icing simulations. This is problematic for predict...
Article
Full-text available
The wake vortices of an aircraft descend by self-induction that enables a pilot to identify approximate wake location based on the preceding aircraft path. A pilot taking off an aircraft can avoid a wake vortex encounter by performing early rotation and flying at or above the climb path of the preceding aircraft. Such operation results in a situati...
Article
Naval helicopters flying at extremely low altitudes often face communication problems when the helicopter is located in the distance from the mother ship. Accordingly, new attention is being cast on the high altitude balloon (HAB) to solve this problem due to its cost-effectiveness and ability of rapid deployment to the battlefield. The balloon is...
Article
Full-text available
Understanding ice accretion and aerodynamic performance degradation is essential in any aircraft certification program to ensure safe flight in icing conditions. In addition to well-known meteorological icing parameters and flight conditions, several physical and modeling parameters are known to play a critical role in the simulation of ice accreti...
Article
Downwash effect is the interaction between rotor wake and a launched rocket. Since the effect alters the initial motion of the rocket, a comprehensive analysis of the effect is crucial in predicting the entire trajectory and range of the rocket. In addition, external winds affect the trajectory and range as the winds alter the downwash effect. Beca...
Article
One of the critical issues in recent ice prediction studies is the modeling of roughness formation based on physical phenomena. While a number of experimental studies have been conducted to investigate the fundamental physics of roughness formation, initial bead growth is rarely studied despite its significance to determine bead size and distributi...
Article
A reasonable solution to retrieve a payload of a scientific balloon regardless of safety issues and recoverability is the sea recovery strategy. Sea recovery strategy is a unique retrieval method being pioneered by the Japan Aerospace Exploration Agency (JAXA) and the Institute of Space and Astronautical Science (ISAS) for decades. This strategy ha...
Article
High performance film cooling holes with complicated geometries have been regarded as impractical up to now because of manufacturability issues. However, recent advances in additive manufacturing (AM) technology have opened up new doors. Investigating characteristics of film holes built with AM, and finding the optimum shape considering these chara...
Article
In this paper, a conceptual design for a reusable unmanned space vehicle was studied with multiple objective functions. To achieve this goal, a multi-objective genetic algorithm was used, and the performance of the space vehicle was evaluated based on weight, propulsion, aerothermodynamics, and trajectory analysis. Minimization of weight and landin...
Conference Paper
In this study, a conceptual design of a reusable unmanned space vehicle with multi-objective functions is conducted. To do that, the multi-objective genetic algorithm (MOGA) was used. To evaluate the performance of the space vehicles, several discipline were analyzed; weight, propulsion, aerothermodynamic and trajectory analysis. Three objective fu...
Article
In this study, two types of drag reduction devices (a horizontal plate, and a vertical plate) are used to weaken the downwash of the upper flow and c-pillar vortex of the DrivAer notchback model driving at high speed (140 km/h). By analyzing and comparing 15 cases in total, the aerodynamic drag reduction mechanism can be used in the development of...
Article
In spite of its crucial importance, conjugate heat transfer has been ignored in most film-hole-array optimization studies due to the burdensome associated with added complexity and computational requirements. To cope with this issue and to consider the conduction cooling effects, the hierarchical kriging model was applied to optimize the film-cooli...
Conference Paper
High performance film cooling holes with complicated geometries have been regarded as impractical up to now because of manufacturability issues. However, recent advances in additive manufacturing (AM) technology have opened up new doors. Investigating characteristics of film holes built with AM, and finding the optimum shape considering these chara...
Article
To reduce the aerodynamic drag, the performance of the underbody aerodynamic drag reduction devices was evaluated based on the actual shape of a sedan-type vehicle. An undercover, under-fin, and side air dam were used as the underbody aerodynamic drag reduction devices. In addition, the effects of the interactions based on the combination of the ae...
Article
In this study, the design optimization of a low Reynolds number airfoil is performed for a Mars exploration airplane. To achieve this goal, a multi-objective genetic algorithm (MOGA) using the Kriging model is used for optimization and a γ–Reθ model is adopted to predict the laminar-turbulent transition point on the airfoil. Both PARSEC and NURBS r...
Conference Paper
In this study, conceptual design for reusable unmanned space vehicle is performed with multiple objective functions. To achieve this goal, Multi-Objective Genetic Algorithm (MOGA) is used and the performance of the space vehicles were evaluated through weight, propulsion, aerothermodynamic and trajectory analysis. For the objective functions, weigh...
Article
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 the hierarchical kriging model is used as a surrogate model. The hierarchical kriging model is one sort of variable-fidelity modeling, which mimics the...
Article
The attenuation of wingtip/blade vortices has been one of the primary concerns in aviation safety and blade-vortex noise. In an effort to effectively dissipate the vortex intensity, a trailing-edge (TE) chipped wing concept was suggested. In this study, to exploit the potential of the chipped wingtip concept for alleviating the tip vortex, a series...
Article
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 manufacturing tolerance has substantial effects on the performance of film cooling, the studies on this issue are even scarcer. The present study propose...
Article
Full-text available
A design optimization method is applied for the flow path design of RBCC engine, an important factor for the determining the propulsion performance operating at air-breathing mode. A design optimization was carried out to maximize the specific impulse of the RBCC engine by using a genetic algorithm based on the Kriging model. Results are analyzed u...
Article
The purpose of this study is to optimize the 1st stage of the transonic high pressure turbine (HPT) for enhancement of aerodynamic performance. Isentropic total-to-total efficiency is designated as the objective function. Since the isentropic efficiency can be improved through modifying the geometry of vane and rotor blade, lean angle and sweep ang...
Article
Before launching a scientific balloon, one needs to precisely predict its trajectory to avoid any possible accidents, as there are no means to control the horizontal motion of the balloon once it is launched. Although earlier studies developed simulation programs that predicted the trajectory of a scientific balloon with reasonable accuracy, the si...
Conference Paper
In this study, the design optimization of low Reynolds number airfoil is performed for Mars exploration airplane. To achieve this goal, MOGA (Multi-Objective Genetic Algorithm) with Kriging model is used for optimization and γ - Reθ model is adopted to predict laminar-turbulent transition point on airfoil. Both PARSEC and NURBS representations are...
Article
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,...
Article
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 res...
Article
A modified method has been suggested to improve the computational efficiency of a multiresolution analysis for implicit temporal integrations. The fundamental idea behind multiresolution analysis is that high cost computations such as flux evaluation are performed only at the cells where the salient flow features exist, thereby reducing the computa...
Conference Paper
Although a plethora of high-performance film cooling hole configurations have been suggested, they are too complicated to manufacture and extremely difficult to maintain their original shapes during turbine operation. Thus, it is assumed that there is little room for further performance improvement by optimizing a single hole shape. However, optimi...
Conference Paper
In the present study, the optimized configurations of film cooled turbine guide vanes proposed in Part I were validated experimentally and the effect of coolant mass flow rate on the performance was examined for those optimized configurations. A set of tests were conducted using an annular sector transonic turbine cascade test facility in Korea Aer...
Conference Paper
In spite of a myriad of researches on the optimal shape of film cooling holes, only a few attempts have been made to optimize the hole arrangement for film cooling so far. Moreover, although the general scale of film cooling hole is so small that manufacturing tolerance has substantial effects on the cooling performance of turbine, the researches o...
Conference Paper
Full-text available
This study is performed to enhance the efficiency of the Reduced Order Model (ROM) for static aerodynamic analysis using Computational Fluid Dynamics (CFD) and Variable Fidelity Modeling (VFM). The Proper Orthogonal Decomposition (POD) and the artificial neural network are used for the ROM. Towards this end, the basis vectors reproducing the behavi...
Article
Full-text available
The 2^{nd} generation ice accretion analysis program has been developed and validated for various icing conditions. The essential feature of the 2^{nd} generation code lies in its capability of handling general 3-D geometry and improved accuracy. The entire velocity fields are obtained based on Navier-Stokes equations in order to take the massively...
Article
Full-text available
This study conducts shape optimization of rib turbulator on the internal cooling passage that has triangular cross-section of high pressure turbine nozzle. During optimization, various types of rib turbulator including angled, V-shaped, A-shaped and angled rib with intersecting rib are considered. Each type of rib turbulator is parameterized with a...
Article
Full-text available
In the present work, design optimization of film-cooling hole array on the pressure side of high pressure turbine nozzle was conducted. There are four rows of fan-shaped film cooling holes on the nozzle pressure side surface and each row has a straight array of holes in the spanwise direction for baseline model. For design optimization, hole distri...
Article
The purpose of this study was to develop an improved actuator surface model for wind turbine analyses. A new actuator surface model based on the lifting line theory has been suggested to eliminate the unexpected induced velocity due to the circulation, as well as to estimate the span-wise and chord-wise variation of the circulation of the blade. In...
Article
The shock buffet on a transonic transport aircraft are negative factors that reduce the aerodynamic performance of aircraft. The parametric studies were performed for position of nacelle/pylon to estimate the trend of flow mechanism under the wing that affects shock buffet. To generate external mesh of aircraft configuration that change the positio...
Article
The shedding of strong vortices generated during take-off and landing poses serious hazards for the following aircraft. To circumvent the vortex wake hazard, a chipped wingtip shape was suggested, and a series of numerical simulations were conducted to verify the conceptual validity of such shape. Numerical simulation was performed by using the inc...
Article
Full-text available
In this study, analyzed the aerodynamic characteristics of Kline-Fogleman airfoils and wings with those more efficiency at low Reynolds number. It was found that lift to drag ratio is enhanced in the range of Reynolds number below 2.4{\times}10^5, especially, can be improved up to 26% at Reynolds number is 1{\times}10^4. It was confirmed that the m...