Online control of critical speed vibrations of a single-span rotor by a rotor dynamic vibration absorber at different installation positions

Hang-ling Hu,Li-dong He 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5

The serious vibration of rotors around the critical speed is a problem in rotor systems. To overcome this problem, a single-span twodisk rotor bench was built to simulate the starting process of a rotor. A new Rotor dynamic vibration absorber (RDVA) was designed and installed in the middle of the rotor. A on-off control method based on speed was applied to control the on-off position of the electromagnet in RDVA. Therefore, the natural frequencies between two selected values could be changed. The principles for the vibration control of the rotor system were studied. The vibration suppression performance of an RDVA is a function of its location. The location of the RDVA is subject to several constraints due to the compact structure of the rotor system. As a result, RDVA cannot always be installed at the optimal location of vibration suppression. Accordingly, a study was performed to observe the effect of RDVA location on the vibration suppression performance. Results showed that installing RDVA with on-off control between the two disks not only suppressed the violent vibrations of the rotor at critical speed during the starting process but also avoided the two resonance peaks generated by the traditional absorber. RDVA maintained the vibration of the rotor at a low level in the entire speed range. Furthermore, the vibrations of the rotor system decreased by 20 % when RDVA was installed near the rotor support.

로터 간격에 따른 쿼드로터의 후류특성 변화 연구

이승철(Seungcheol Lee),채석봉(Seokbong Chae),김주하(Jooha Kim) 한국가시화정보학회 2019 한국가시화정보학회지 Vol.17 No.3

Rotor wake interaction must be considered to understand the quadrotor flight, and the rotor separation distance is an important parameter that affects the rotor wake interaction. In this study, the wake characteristics were investigated with varying the rotor separation distance. The velocity field in the rotor wake was measured using digital PIV for hovering mode at Re = 34,000, and the wake boundaries from the inner and outer rotor tips were quantitatively compared with varying the rotor separation distance. The symmetric rotor-tip vortex shedding about the rotor axis was found at a large rotor separation distance. However, the wake boundary became more asymmetric about the rotor axis with decreasing the rotor separation distance. At the minimum rotor separation distance, in particular, a faster vortex decay was observed due to a strong vortex interaction between adjacent rotors.

Intermeshing Rotor의 구조가 SBR/BR 합성고무 복합소재의 실리카 분산에 미치는 영향의 비교

김성민(Sung Min Kim),김광제(Kwang Jea Kim) 한국고분자학회 2012 폴리머 Vol.36 No.5

실리카로 충전된 SBR(styrene butadiene rubber)/BR(butadiene rubber) 합성고무 복합소재에 대해서 가공기기 의 구조가 실리카 분산에 미치는 영향을 파악하기 위해 주사전자 현미경(SEM-scanning electron microscope)을 이용하여 컴파운드의 모폴로지를 관찰하였다. Internal mixer 내에서 intermeshing rotor와 tangential rotor에 의해 배합된 컴파운드를 비교한 결과, intermeshing rotor에 의해 가공되었을 경우 실리카 입자가 더 고르게 분산 및 분포되었음을 관찰하였다. Rotor의 geometry 차이에 의해 intermeshing rotor가 tangential rotor보다 더 큰 전단력(shear)을 컴파운드에 전달하여 실리카 입자를 효과적으로 분산 및 분배시킨 것으로 판단된다. The effects of mixing geometry (intermeshing vs. tangential rotor) for the dispersion and distribution of silica agglomerates in SBR/BR compound were investigated. Silica dispersion and distribution were found to be better with the intermeshing rotor compared to the tangential rotor. It was concluded that the intermeshing rotor compared to the tangential rotor delivered a higher shear stress due to interlocked rotor geometry to silica agglomerates leading to better dispersity and distribution of silica in the agglomerates.

Dynamic Modeling and Stabilization Techniques for Tri-Rotor Unmanned Aerial Vehicles

Dong-Wan Yoo,Hyon-Dong Oh,Dae-Yeon Won,Min-Jea Tahk 한국항공우주학회 2010 International Journal of Aeronautical and Space Sc Vol.11 No.3

The design, dynamics, and control allocation of tri-rotor unmanned aerial vehicles (UAVs) are introduced in this paper. A trirotor UAV has three rotor axes that are equidistant from its center of gravity. Two designs of tri-rotor UAV are introduced in this paper. The single tri-rotor UAV has a servo-motor that is installed on one of the three rotors, which enables rapid control of its motion and its various attitude changes?unlike a quad-rotor UAV that depends only on the angular velocities of four rotors for control. The other design is called ‘coaxial tri-rotor UAV,’ which has two rotors installed on each rotor axis. Since the tri-rotor type of UAV has the yawing problem induced from an unpaired rotor’s reaction torque, it is necessary to derive accurate dynamic and design control logic for both single and coaxial tri-rotors. For that reason, a control strategy is proposed for each type of trirotor, and nonlinear simulations of the altitude, Euler angle, and angular velocity responses are conducted by using a classical proportional-integral-derivative controller. Simulation results show that the proposed control strategies are appropriate for the control of single and coaxial tri-rotor UAVs.

Dynamic Modeling and Stabilization Techniques for Tri-Rotor Unmanned Aerial Vehicles

Yoo, Dong-Wan,Oh, Hyon-Dong,Won, Dae-Yeon,Tahk, Min-Jea The Korean Society for Aeronautical and Space Scie 2010 International Journal of Aeronautical and Space Sc Vol.11 No.3

The design, dynamics, and control allocation of tri-rotor unmanned aerial vehicles (UAVs) are introduced in this paper. A trirotor UAV has three rotor axes that are equidistant from its center of gravity. Two designs of tri-rotor UAV are introduced in this paper. The single tri-rotor UAV has a servo-motor that is installed on one of the three rotors, which enables rapid control of its motion and its various attitude changes-unlike a quad-rotor UAV that depends only on the angular velocities of four rotors for control. The other design is called 'coaxial tri-rotor UAV,' which has two rotors installed on each rotor axis. Since the tri-rotor type of UAV has the yawing problem induced from an unpaired rotor's reaction torque, it is necessary to derive accurate dynamic and design control logic for both single and coaxial tri-rotors. For that reason, a control strategy is proposed for each type of tri-rotor, and nonlinear simulations of the altitude, Euler angle, and angular velocity responses are conducted by using a classical proportional-integral-derivative controller. Simulation results show that the proposed control strategies are appropriate for the control of single and coaxial tri-rotor UAVs.

Impact of surface roughness on gas turbine engine fan and compressor rotor

Ashima Malhotra,Shraman Goswami,A. M. Pradeep 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.5

A gas turbine engine, being an open cycle engine, gets exposed to atmospheric conditions through the intake of air from the surroundings. Debris of different sizes comes into the engine through the fan inlet and impinges on the different components inside the engine, making them rough. Another source of roughness is encountered with the manufacturing process itself. Hence it is important to understand the impact of surface roughness on the performance of either an engine in the field or a newly designed engine. The current work focuses on the performance impact of surface roughness on a fan rotor and a compressor rotor. The flow field is numerically studied with and without roughness. The flow field of a fan rotor is generally different from a compressor rotor, specifically in terms of shock structure and secondary flow, and hence a comparative study is made to understand the impact of roughness in presence of different flow fields. The NASA rotor67 (fan rotor) and the NASA rotor37 (compressor rotor) are used for the numerical study carried out for this work. The results indicate that the extent of performance loss is more for compressor rotor (NASA rotor37) for same amount of roughness used on fan and compressor rotor. A detailed flow field investigation from the numerical study is presented to understand the reason behind the different extents of performance loss. It is found that not only the amount of roughness but also the flow field plays a significant role on the performance of a gas turbine engine fan and compressor rotor.

OpenFOAM 해석자 알고리즘 확장을 통한 Actuator Disk 기반의 로터 성능 해석자 개발

김태우(T. Kim),오세종(S. Oh),강희정(H. J. Kang),이관중(K. Yee) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5

The purpose of this study is to develop and verify the newly developed solver for analyzing rotor flow field using the open-source CFD code. For helicopter fuselage aerodynamic evaluations an actuator disc model is sufficient unless a transient solution is sought that requires the modeling of the passage of the blades and associated tip vortices. In the present study, a rotor analysis solver has the formal algorithm of SIMPLE in simpleFoam, and the individual procedure for considering rotor influence. The flow chart of rotor analysis solver algorithm. The flow field around complex rotor-fuselage configurations can be modeled as a simple single block grid with unstructured meshes. For the calculation of the rotor thrust, the virtual blade method based on the blade element theory is employed. The inflow velocities on the rotor disk used to specify the effective angles of attack, have been included in the solver. The time-averaged mean flow of the unsteady rotor in forward flight is calculated by modeling the rotor as an actuator disk in which source term is added in the momentum equation. The ROBIN configuration is designed for the experimental study of rotor-fuselage interactional aerodynamics and inflow analysis. The time-averaged inflow velocity is normalized by the rotor tip rotational speed and compared with the experimental data at four azimuthal positions for the rotor-fuselage configuration with or without the fuselage at the test conditions. For hovering validation, caradonnas and ballard’s experiments were employed. The validation cases in forward and hovering flight were computed and good agreement with the experiment is obtained. It is demonstrated that the present method for estimation of rotor influence and OpenFOAM for numerical fluid analysis could a useful tool to predict the complicated rotor-fuselage interactional aerodynamic phenomena and to estimate inflow on rotor disk in an efficient time-averaged manner.

Effect of cooling flow on thermal performance of a gas foil bearing floating on a hot rotor

심규호,이용복,송진우,김태호 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5

This paper presents the measurements of the thermal behavior of a gas foil bearing (GFB) floating on a hot rotor in a tangential air injection cooling scheme. The cooling air was tangentially injected against rotor spinning into the inlet mixing zone of the test GFB. The hollow rotor was heated by a cartridge heater. The GFB temperatures were measured at intervals of 30 deg along the circumference of the axial center except for at 45 deg, where the cooling flow is injected. The rotor temperatures were measured near the GFB side ends using an infrared thermometer, which was calibrated with a thermocouple. Load cells measure the static load and bearing torque. The baseline rotor temperature was measured without GFB over the axial length at rotor speeds up to 15 krpm and for increasing heater temperatures up to 400 °C. The results showed relatively uniform rotor temperatures at the test journal GFB section, and severe heat convections on the rotor surfaces. The GFB and rotor temperatures were measured under a static load of 80 N for increasing heater temperatures of 100 °C, 200 °C, 300 °C and 400 °C and with increasing cooling flow rates of 100 liter/min, 150 liter/min, and 200 liter/min. The circumferential GFB temperatures showed the maximum temperatures at the loaded zone and the minimum temperatures in the unloaded zone. The increasing cooling flow effectively reduced both the rotor and GFB temperatures, showing a dramatic decrease with the smallest amount of cooling flow. GFB friction torque was measured for two test cases for the static load of 80 N at a rotor speed of 10 krpm:1) A lift-off and touch-down operating cycle for increasing heater temperatures without the cooling flow, and 2) a continuous operation for the heater temperature of 400 °C with increasing cooling flows. In test case 1, the GFB friction torque decreased for higher heater temperatures due to a larger thermal expansion of the bearing housing than the rotor’s. In test case 2, the GFB friction torque decreased with increasing cooling flows due to strong cooling effects on the rotor temperature. The results imply that the tangential air injection increased the GFB clearance by directly cooling the rotor and effectively alleviating the rotor expansion; hence, the scheme is capable of an effective cooling for high temperature GFB applications, such as micro gas turbines.

Combined effects of channel curvature and rotor configuration on the performance of two-stage viscous micropumps

강동진 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.6

The combined effects of channel curvature and rotor configuration on the performance of two-stage viscous micropumps were studiednumerically. The Navier-Stokes equations were simulated to investigate the performance of two-stage micropumps. The performance oftwo-stage micropumps was studied in terms of the dimensionless mass flow rate and dimensionless driving power. Four different rotorconfigurations were designed by changing placement of two rotors inside a microchannel: Two aligned and two staggered configurations. The aligned rotor configuration of type 1 is to place the two rotors along the convex wall, while type 2 is to place them along the concavewall. Numerical results show that the rotor configuration plays a significant role in the performance of two-stage micropumps. The channelcurvature acts in a different way according to the rotor configuration. The mass flow rate of aligned rotor configuration of type 1 isgreatly improved by the channel curvature, while it diminishes the mass flow rate of type 2. The maximum mass flow rate for the alignedrotor configuration of type 1 is obtained when the two rotors are placed at the junction of the circular and straight sections of the channel. The performance of staggered configurations is negligibly affected by the channel curvature. This characteristics is found due to rotationdirection of the rotors. As the two rotors rotate in the opposite direction for the staggered configurations, the flow characteristics in thecircular section is little affected by the channel curvature. The circumferential distance between the two rotors can be optimized in termsof the mass flow rate. The optimal value of the circumferential distance is about L = 1.4 for the staggered rotor configurations, and it isalmost independent of the channel curvature. As the channel height increases, the circumferential distance becomes less significant forthe staggered rotor configurations while it becomes significant for the aligned rotor configurations.

수직 하강 비행 시 로터-로터 상호작용이 UAV의 후류 구조에 미치는 영향

채석봉(Seokbong Chae),이승철(Seungcheol Lee),김주하(Jooha Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

In the present study, we experimentally investigate the effect of rotor-rotor interaction on the rotor wake structure in axial descent. A twin rotor configuration system with various rotor separation distances were installed in the closed-circuited wind tunnel to observe wake structures of rotors in axial descent. Velocity fields around twin rotors were measured by using DPIV(digital particle image velocimetry). At a range of descent rate of V<SUB>d</SUB>/V<SUB>h</SUB> = 1.08 – 1.52 and a high rotor separation distance (s/R = 2.5), the flow around rotor enters VRS(vortex ring state), which form a large recirculation zone near the rotor tip. However, a decrease in s/R induces a stronger effect of rotor-rotor interaction on the rotor wake, resulting in the change in the location of a vortex ring core. At a very low s/R of 0.25, rotor-rotor interactions disrupt the vortex ring structure and make synthetic jets with the adjacent rotor wake. At various rotor separation distances, the frequency of vortex ring state was analyzed through the correlation analysis. At V<SUB>d</SUB>/V<SUB>h</SUB> = 1.08, the frequency of vortex ring decreases gradually as the rotor separation distance decreases and reach less than half at s/R = 1.5.