• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.813-824
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• 2004

The paper studies the effect of neighboring blade rows on flutter characteristics of cascading blades. For this purpose the computation program to calculate the unsteady blade loading based on the un-steady lifting surface theory for contra-rotating annular cascades was formulated and coded. Then a computation program to solve the coupled bending-torsion flutter equation for the contra-rotating annular cascades was also developed. Some results of the flutter analysis are presented. The presence of the neighboring blade row gives rise to significant change in the critical flutter condition when the main acoustic duct mode is of cut-on state.

• International Journal of Aerospace System Engineering
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• v.8 no.1
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• pp.1-13
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• 2021

Contra-rotating fan is comprised of two rotors which are rotating in the opposite direction. The fan stages are named rotor-1 and rotor-2. Benefits from the use of contra rotation are in terms of better efficiency and improved thrust to weight ratio. Failure of contra-rotating fan stage blade in-service results in safety risks, repair costs, and revenue losses. This paper focuses on the vibration analysis and one way fluid-structure interaction of high aspect ratio, low speed contrarotating fan rotors. Modal analysis and modal pre-stress analysis of contra-rotating fan rotors were carried out to calculate the natural frequencies, One way fluid-structure interaction (FSI) was carried out where the computational analysis of the blades was performed using ANSYS CFX. The boundary conditions for CFD analysis were considered from the actual experimental velocity flow field at the inlet and pressure outlet. Based on the results obtained from the CFD analysis, the structural analysis such as deformation and Von-Misses stresses was carried out by using the finite element method (FEM) with ANSYS. The results provide necessary guidelines for the safe running of the contra-rotating fan. The analysis also will be helpful to understand the change of flow behavior due to a rotor deformation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.300-303
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• 2006

The rotor blade of a helicopter is the key structural units and provides three components such as vertical lifting force, horizontal propulsive force and control force. With advancements in aerospace technology, composite materials have been widely used in lightweight structures. In addition, composites show great potential on the design of rotor blades due to the advantages of strength, durability and weight of the materials. In the operational condition of a helicopter, it is required the vibration characteristics of the rotating blades for avoiding resonance and analysis of efficient performance prediction et al. In this study, the CAMRAD-II is used for analyzing the vibration characteristics of rotating composite blades. The effects of rotating speed and collective angles are investigated. Also, the numerical results are compared with experimental data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.680-681
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• 2012

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1172-1178
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• 2006

Measurement of blade strain with sensors directly installed on the blade has one critical issue, how to send the sensor signal to the ground. Strain-gauges have been dominantly used to directly measure stress of a blade and either a slip ring or a telemetry system has to be used to send measured signal to the ground. However, both systems have many inherent problems and sometimes very severe limitations to be practically used. In this paper, new on-line strain monitoring method using. FBG(Fiber Bragg Grating) sensors and a beam coupler is introduced. Measurement of rotor stress using FBG sensors is nothing new, but unlike other system which installs all necessary instruments on the rotor and use telemetry system to send data to the ground, this system makes use of light's unique characteristic - light travels through space. In this new approach, single optical fiber with many FBG sensors is installed on the blade and all other necessary instruments can be installed at ground thereby giving tremendous advantages over slip ring or telemetry system. A reference sensor is also introduced to compensate the beam coupler's transmission loss change due to rotation. The suggested system's good performance is demonstrated with experiments.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.519-533
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• 2023

This work focuses on the dynamic analysis of thermal barrier coated straight and curved turbine blades modelled as functionally graded sandwich panel under thermal environment. The pre- twisted straight/curved blade model is considered to be fixed to the hub and, the complete assembly of the hub and blade are assumed to be rotating. The functionally graded sandwich composite blade is comprised of functionally graded face-sheet material and metal alloy core. The constituents' material properties are assumed to be temperature-dependent, however, the overall properties are evaluated using Voigt's micromechanical scheme in conjunction with the modified power-law functions. The blade model kinematics is based on the equivalent single-layer shear deformation theory. The equations of motion are derived using the extended Hamilton's principle by including the effect of centrifugal forces, and further solved via 2D- isoparametric finite element approximations. The mesh refinement and validation tests are performed to illustrate the stability and accurateness of the present model. In addition, frequency characteristics of the pre-twisted rotating sandwich blades are computed under thermal environment at various sets of parametric conditions such as twist angles, thickness ratios, aspect ratios, layer thickness ratios, volume fractions, rotational velocity and blade curvatures which can be further useful for designing the blade type structures under turbine operating conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.12-21
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• 2010

This paper focuses on the hover performance experiment of a small-scale single rotor in partial ground conditions. In this study, small-scale rotor blade rotating device and floor panel are used to include partial ground effect. Thrust and torque were measured with varying collective pitch angles at fixed rotor rotating speed. The overlap distance between rotor and ground is d, the rotor diameter is D. It was shown that the ground effects have little effect on the rotor performance until d/D is 0.25. Four blade rotor has more increased thrust and more reduced power than those of two blade rotor because of stronger ground effect. In addition, it was also found that the thrust increases as a collective pitch angle become smaller. Based on these experiment results, we deduced new empirical equation considered blade number and partial ground effect.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1249-1259
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• 2002

The present study investigates the convective heat/mass transfer inside a cooling passage of rotating gas-turbine blades. The rotating duct has various configurations made of ribs with 70。 attack angle, which are attached on leading and trailing surfaces. A naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. The present experiments employ two-surface heating conditions in the rotating duct because the surfaces, exposed to hot gas stream, are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. In the stationary conditions, the parallel rib arrangement presents higher heat/mass transfer characteristics in the first pass, however, these characteristics disappear in the second pass due to the turning effects. In the rotating conditions, the cross rib present less heat/mass transfer discrepancy between the leading and the trailing surfaces in the first pass. In the second pass, the heat/mass transfer characteristics are much more complex due to the combined effects of the angled ribs, the sharp fuming and the rotation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.68-75
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• 2007

A three-dimensional computation is conducted to simulate a three-dimensional rotating stall in a low speed axial compressor. It is generally known that a tip leakage flow has an important role on a stall inception. However, almost of researchers have taken no interest in a role of the hub-comer-stall on the rotating stall even though it is a common feature of the flow in an axial compressor operating near stall and it has a large effect on the flows and loss characteristics. Using a time-accurate unsteady simulation, it is found that the hub-comer-stall may be a trigger to collapse the axisymmetric flows under high loads. An asymmetric disturbance is initially originated in the hub-comer-stall because separations are naturally unstable flow phenomena. Then this disturbance is transferred to the tip leakage flows from the hub-comer-stall and grows to be stationary stall cells, which adheres to blade passage and rotate at the same speed as the rotor. When stationary stall cells reach a critical size, these cells then move along the blade row and become a short-length-scale rotating stall. The rotational speed of stall cells quickly comes down to 79 percent of rotor so they rotate in the opposite direction to the rotor blades in the rotating frame.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.453-460
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• 2000

A test rig is developed for performance test of 1 stage axial-type turbine which is designed by meanline analysis, streamline curvature method, and blade design method using configuration parameters. The purpose of this study is to find the best configuration parameters for designing a high efficiency axial-type turbine blade. To measure the efficiency of turbine stage, a dynamo-meter is installed. Two different stators which are manufactured as an integrated type are developed, and a rotor blade and 5 sets disc are developed for setting different stagger angle. The tip and hub diameters of the test turbine are 300 and 206.4mm, respectively. The rotating speed is 1800RPM, and the extracted power is 2.5kW. Flow coefficient is 1.68 and the reaction factor at meanline is 0.373. The number of stator and rotor of test turbine are 31 and 41, respectively. The Mach number of stator exit flow near hub is 0.164.