Jong-Soo Choi

Chungnam National University | CNU · Department of Aerospace Engineering

Most recently developed drones are based on four or more distributed multi-propulsion systems. In addition, there have been attempts to apply the multi-propulsion system to urban air mobility as well as drones. As these new flight vehicles are required to operate closer to the city, the noise reduction issue has to be considered more extensively. T...

This paper identifies the phase lag of a coaxial helicopter UAV to remove the effect of the structural vibration and rotor wake by improper phase lag. This vibration affects the sensor measurement of the flight control computer and deteriorates the attitude control performance of the internal controller. The characteristics that depend on the phase...

Floating ring seals are widely used as a leakage control solution for turbomachines because they effectively operate with small clearances between the shaft and seal. The oxidizer pump of the 7 tonf liquid engine in the Korea Space Launch Vehicle II (KSLV-II) operates at high rotational speeds and under cryogenic conditions and has floating ring se...

The demand for new propeller designs has increased alongside the development of new technology, such as urban aircraft and large unmanned aerial vehicles. In order to experimentally identify the performance of a propeller, a wind tunnel that provides the operating flow is essential. However, in the case of a meter class or larger propeller, a large...

Currently, the detection of targets using drone-mounted imaging equipment is a very useful technique and is being utilized in many areas. In this study, we focus on acoustic signal detection with a drone detecting targets where sounds occur, unlike image-based detection. We implement a system in which a drone detects acoustic sources above the grou...

This article describes a wind tunnel experiment that was undertaken to investigate the changes in the aerodynamic performance of a wind turbine due to the inclusion of a 2D airfoil with a serrated trailing edge designed to reduce the noise caused by a wind turbine rotor blade. The restrictive condition for the serrated trailing edge equipped with t...

This work conducts a validation study for the XH-59A helicopter using a rigid coaxial rotor system in order to establish the techniques of the conceptual design and performance analysis for the lift-offset compound rotorcraft. As a tool for conceptual design and performance analysis, NDARC (NASA Design and Analysis of Rotorcraft) is used for the pr...

This paper discussed a noise reduction effect of airfoil and small-scale model rotor by using attached serration trailing edge in the wind tunnel test condition. In order to analyze the changes in the performance due to the inclusion of a serrated trailing edge designed to reduce noise, a 10 kW wind turbine rotor was equipped with a thin serrated t...

Position estimation of sound source using ray tracing method is introduced based on wind field measurement. TDOA (time difference of arrival) estimate error occurs during outdoor sound measurement due to the atmospheric condition such as wind, temperature, humidity and so on. Such condition can possibly change the trajectories of rays. It produces...

This study presents an application of acoustic source localization using microphone array installed on a drone. Although recent technology of drone enables to record audio and video, there are still acoustic problems such as engine noise, propeller-induced flow noise, microphone directivity, etc. Such unwanted noise shows strong tonal characteristi...

A validation study is conducted for the conceptual design and performance analysis of UH-60A Black Hawk in order to establish the conceptual design and performance analysis techniques for conventional helicopters using a single main rotor and a tail rotor. As a tool for conceptual design and analysis, NDARC(NASA Design and Analysis of Rotorcraft) i...

TDOA(time delay of arrival) position estimate from acoustic measurement of artillery shell impact is studied in order to develop a targeting evaluation system. Impact position is calculated from the intersections of hyperbolic estimates based on the least square Taylor series method. The mathematical process of Taylor series estimation is known to...

A technique for improving estimation accuracy is introduced in order to locate the impact position of artillery shell during the weapon scoring test. Study on localization of impacts using acoustic measurement has been conducted and the usability of sensor array is verified with experiments. When the blast occurs above the ground in the firing rang...

This paper presents an application of an optimal smoothing filter for moving target tracking problem based on measured noise source. In order to measure distance and velocity for the moving target, a beamforming method is applied to use the noise source by using microphone array. Also a Kalman filter and an optimal smoothing algorithm are adopted t...

A methodology is proposed to estimate a trajectory of a flying target and its velocity using the time and frequency analysis of the acoustic signal. The measurement of sound emitted from a flying acoustic source with a microphone above a ground shall receive both direct and ground-reflected sound waves. For certain frequency contents, the destructi...

This paper is the study on the establishment of design model to improve design efficiency using modified weight estimation equation on the initial design stage for development of a helicopter. The methodology to extract coefficients of the weight estimation equation was proposed through the influence investigation for the weight of components and t...

The helicopter initial design model was established by using the latest weight estimation equations based on the Tishchenko`s methodology through the study existing initial design tools. The sequential decomposition method is used to reduce analysis time in the sizing. Empirical parameters of the weight estimation equation were also extracted from...

This paper presents an application of optimal smoothing algorithm for a model rocket trajectory based on beamforming data using microphone array. The model rocket is designed to move along a one degree of freedom linear wire guide for measuring the sound waves transmitted from a fast moving compact source in outdoor environment. The peak value of t...

This paper conducts the aeromechanics study using the two different rotorcraft computational structural dynamics (CSD) codes, CAMRAD II and DYMORE II, for the rotor in low-speed descending flight. The three test cases of the HART (Higher-harmonic control Aeroacoustic Rotor Test) I-baseline, minimum noise, and minimum vibrationare considered for the...

In this work, we are interested in tracking a rotating sound source using a Kalman filtering technique based on a set of non-linear time difference of arrival (TDOA) measurements. Array of microphones measure acoustic signal emitted from a rotating source and the TDOA estimates are calculated followed by a solution for hyperbolic position fix. The...

In this paper, wind tunnel test and analytical prediction are compared for result of flapping motion in helicopter forward flight condition. Tests were performed at low speed wind tunnel at Chungnam National University, test section of wind tunnel has 1.8 by 1.8 meter open-jet test section area. According to the results of measured data for aerodyn...

To reduce airfoil self-noise from a 10 kW wind turbine, we modified the airfoil shape and planform of a wind turbine blade. To obtain the optimal blade design, we used optimization techniques based on genetic algorithms. The optimized airfoil was first determined based on a section of the rotor blade, and then the optimized blade was designed with...

This article investigates the effect of asymmetric wing damage on flight dynamic characteristics of a flying-wing single motor unmanned air vehicle. To construct a six degree-of-freedom model of the damaged aircraft, a flying-wing type unmanned aerial vehicle is designed, and the wind tunnel test for damaged configurations is performed to identify...

This paper discussed a procedure for noise certification of Aircraft and predicting the full scale over-flight noise of propeller from acoustic wind tunnel measurement of small scale propeller. Noise Certification Procedures is established from International Civil Aviation Organization(ICAO). The data manipulations are then discussed in extrapolati...

The localization of sound sources in a three dimensional space has been recognized as an important research topic in acoustics. Many acoustic measurement techniques in three-dimensional space have used spherical shape of array to optimize sensor configuration and increase its performance and spatial resolution. In this study, the design of micropho...

In this paper, a series of experiment is performed for a scaled hovering rotor in a semi-anechoic chamber and the results are compared to the noise spectra predicted by using Lowson's loading noise equation and FW-H equation. It was founded that the sound directivity pattern for both experiments and predictions are similar in their trend. Meanwhile...

As considerable interests in noise emission from a ship have been increased, the need for localization of noise sources of the marine propeller generating cavitation and singing noise is looming large. In many practical cases, cavitation and singing noise occur on a particular position of the certain blade of the propeller. It is so important to kn...

Recent development of signal processing technologies has encouraged the aero-acousticians to implement the state-of-the-art sensors and data acquisition devices. They sometimes cost too much; however, especially for the academic arenas, the efforts of reducing the expense of integrating a system and increasing performance of phased array have initi...

Periodic vortex separations generate periodic vertical forces acting on a trailing edge of an airfoil. When a natural frequency of the trailing edge of the airfoil is close to a vortex shedding frequency, an amplitude of the edge oscillation becomes maximal; it makes intensive noise called singing. Motion of the trailing edge may also feedback to t...

An approach to 3D visualization of multiple sound sources has been developed with the application of a moving array technique. Frequency domain beamforming algorithm is used to generate a beam power map and the sound source is modeled as a point source. When a conventional delay and sum beamformer is used, it is considered that 2D distribution of s...

In this study a 3-component rotating balance, which is designed to measure the thrust (Fz) and two moment components (Mx, My) simultaneously for a rotor test jig, is designed and its performance is validated experimentally. The low voltage signal from the strain gages mounted on the balance is amplified with a rotating amplifier, which is then fed...

The time difference of arrival(TDOA) algorithm is being used widely for identifying the location of a source emanating either electrical or acoustic signal. It's application areas will not be limited to identifying the source at a fixed location, for example the origin of an earthquake, but will also include the trajectory monitoring for a moving s...

Microphone array beamforming method has been recognized as an important aeroacoustic research field and become a standard technique in localizing sound sources. This method also used in flight acoustic measurement, and especially, it is very useful when measure sounds inside the wind tunnel. In measuring sound which is inside the wind tunnel by tra...

Several experimental techniques for identifying the noise sources distributed over a moving vehicle have been developed recently and are used to design a low noise vehicle. The beamforming method, which uses phase information between several microphones to localize the source position, is proved to be one of the promising techniques applicable even...

An impulse turbine, which is a main component of a liquid rocket engine, needs to be a small size with light weight and generate large power. Since the impulse turbine is being operated under complicated supersonic conditions, flow analysis and performance prediction largely depend on CFD technique. In order to increase the reliability of the predi...

this paper the acoustic signature from a supersonic nozzle is measured and compared to the result of a program developed for a gas turbine noise prediction. In order to measure the jet Mach Number, the pressure and temperature at the settling chamber was measured along with pressures from a pitot-tube placed near the exit. The results are also comp...

In the case of aeroacoustic test in windtunnel, measurement accuracy is reduced by not only Doppler effects but also by the microphone self noise due to airflow and high turbulence in the wall boundary layer. Microphone array measurements can be easily utilized for the solutions of these problems. In this paper, geometrical optics approach and diag...

Acoustic analysis of a moving sound source required that the measured sound signals be do-Dopplerized and restored as of the original emission signals. The purpose of this research is development of beamforming technique can be applied to the rotor noise source identification. For the do-Dopplerization and reconstruction of emitted sound wave, Forw...

The positions of rotating sound sources have been localized by experiments with the Doppler effects removed. In order to de-Dopplerize the sound signals emitted from moving sources, two kinds of signal reconstruction methods were applied. One is the forward propagation method and the other is the backward propagation method. Forward propagation met...

This paper presents an acoustic source localization technique on 2D cavity model in flow using a phased microphone array. Investigation was performed on cavity flows of open and closed types. The source distributions on 2D cavity flow were investigated in an anechoic open-jet wind tunnel. The array of microphones was placed outside the flow to meas...

In this paper the aeroacoustic characteristics of a helicopter main rotor system is measured by using a pair of scaled rotor blades. A low noise rotor test jig is developed for noise measurement and the rotational speed, thrust and torque are measured simultaneously in order to match the aerodynamic conditions with the full scale rotor. The accurac...

This paper reports on an experimental investigation of large-scale flowfield instabilities in a pump rotor and the process of noise generation by these instabilities. Measurements of the fluctuating components of velocity and surface pressure were made with hot-wire probes and surface mounted pressure transducers on a seven bladed back swept centri...

The performance of a centrifugal fan depends on the dimensional parameters of impeller, such as the inlet and exit diameter, area ratio, relative flow angles to the blade, and the number of blades. These design parameters, however, are inter-related, so it is very difficult to identify the effect of each parameter on the fan performance. In this ex...

For a cylinder in a uniform flow stream, sound is generated by the fluctuating pressure on the surface of a cylinder due to the vortex shedding behind the cylinder. It is known that the major parameters in predicting the acoustic pressure at the far field are the flow velocity, the correlation length, and the fluctuating lift coefficient. In this e...

The objective of this research is to obtain a better insight into the flowfield in a centrifugal turbomachinery. To investigate this turbomachinery flowfield, measurements have been made with hot-wire sensors at the exit of a centrifugal impeller. The measured data at the discharge show a jet-wake type of flow pattern which results in a strong vort...

The objective of this research was to identify which aspects of the fluid dynamics are associated with noise generation in centrifugal turbomachinery. Research emphasis was placed on the generation of noise at frequencies other than the blade passage tones. In order to avoid noise generated by the interaction of the discharged flow and stationary o...

The objective of this research was to identify which aspects of the fluid dynamics are associated with noise generation in centrifugal turbomachinery. Research emphasis was placed on the generation of noise at frequencies other than the blade passage tones. In order to avoid noise generated by the interaction of the discharged flow and stationary o...

Flow induced noise generation mechanisms in a centrifugal turbomachine are investigated in this study. To isolate the noise generation mechanisms of interest, a simplified discharge configuration was selected. The unsteady flowfield discharging from the rotating impeller has been measured with stationary hot-wire sensors. A space and time cross-cor...

Twisted tubes are important in generating secondary flow and fluid mixing in a cross-stream direction. In the present paper, the fully developed laminar fluid flow through twisted elliptic tubes is numerically analyzed up to a large twist ratio by using the finite difference method. The elliptic solution domain is transformed to a rectangular compu...