• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.3
• /
• pp.498-511
• /
• 2017

This work conducts a validation study for loads analysis of the UH-60A slowed rotor at high advance ratios. The nonlinear flexible multibody dynamics analysis code, DYMORE II, is used with a freewake model for the rotorcraft comprehensive analysis. Wind tunnel test data of airloads and structural loads of a full-scale UH-60A slowed rotor are used for this validation study. This analysis predicts well the thrust reversal phenomenon at the advance ratio of 1.0. The section airloads such as normal forces and pitching moments and the oscillatory blade structural moments in this analysis are compared well or moderately with the measured data, although the higher harmonics components of blade torsion moments are not captured well. This validation study assesses the prediction accuracy and investigates the unique aeromechanics characteristics of a slowed rotor at high advance ratio.

• 연구논문집
• /
• s.22
• /
• pp.5-19
• /
• 1992

An aerodynamic design technique of a centrifugal impeller is developed. The design procedure consists of a preliminary design, a three-dimensional blade surface generation, a flow analysis of impeller passage and a compatibility analysis for the designed impeller. To get a higher efficiency, the backswept impeller which has a lean angle and a parabolic blade surface is designed. In the present analysis of flow in an impeller, an inviscid quasi-three-dimensional method and a viscous three-dimensional method are used. Compatibility of the designed impeller is decided with the results of the analyses. The quasi-three-dimensional method is easy to use, but limited to a few conditions in real application for the prediction of the actual flow in the impeller. Since the viscous three-dimensional method proved to predict the real flow in the impeller relatively well, it can be used as a means for the decision of compatibility of the designed impeller.

• Journal of Power System Engineering
• /
• v.2 no.1
• /
• pp.39-44
• /
• 1998

Computational grids used in the numerical simulation of multi staged turbomachinery flow fields are generated. A multiblock structure simplifies the creation of structured H-grids about complex turbomachinery geometries and facilitate the creation of a grid for multi-row topologies. The numerical algorithm adopts the combination of the algebraic and elliptic method to create the internal grids efficiently and quickly. The input module is made of the results of the preliminary design, i.e., flow-path, aerodynamic conditions along the spanwise direction, and the blade profile data. The final grids generated from each module of the system are used as the preprocessor for the performance prediction of the single row cascades and the flow simulation inside the multi staegd blade passage. Application to low pressure compressor of industrial gas turbine engines was demonstrated to be very reliable and practical in support of design activities.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.54 no.6
• /
• pp.982-988
• /
• 2021

Gamma irradiation is one of the simple methods used to induce mutagenesis. Therefore, it is widely used for the development of breeding lineages of plants and algae. In this study, it was developed a new variety of Pyropia yezoensis using gamma irradiation. It was applied a dose of 1 kGy and named the developed mutant Py1k. The blade with width of the mutant was narrower and the blade length was longer than those of the wild type. To further investigate the mutant, it was analyzed the nutrient composition and antioxidant activity. In comparison to those in the wild type, it was found a higher amino acid composition and marginally increased antioxidant activity in Py1k. Based on these results, it was suggests that our protocol can be utilized to develop Pyropia species with improved nutritional quality through gamma irradiation.

• The KSFM Journal of Fluid Machinery
• /
• v.2 no.3 s.4
• /
• pp.45-51
• /
• 1999

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise due to the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan and to calculate the effects of rotating velocity, flow rate, cut-off distance and the number of blades and its effects on the noise of the fan. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated with the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The cut-off distance is the most important factor effecting the noise generation. Acoustic pressure is proportional to 2.8, which shows the same scaling index as the experimental result. In this paper, the cut-off distance is found to be the dominant parameter offecting the acoustic pressure.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.5
• /
• pp.63-68
• /
• 2017

This study determines the selection of an appropriate jig material for the blade edge of the medical sapphire knife. The physical properties of the jig material affects the edge shape and chipping phenomenon in machining of the medical sapphire knife. If a grinding wheel is used, brittle workpieces such as sapphire are easily damaged by the propagation of cracks because the grinding force significantly increases. It is important to constantly maintain the grinding force in the grinding process of the brittle materials. The grinding force can be kept constantly by inducing the elastic deformation of the Jig material because the elastic deformation of brittle work-piece is negligibly low. The chipping phenomenon may be reduced by selecting the proper Jig material. Aluminum, copper, stainless steels and carbon steel were used as Jig materials. The experiment was conducted using a cast iron grinding wheel, which was installed on a conventional grinding machine with the ELID grinding system. The thickness and width of the chipping area were measured using an optical microscope and FE-SEM to analyze the shape of the blade edge. According to the experiment result, the chipping phenomenon decreased, and the sharp edge was formed when the jig materials with low elastic modulus were used.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.18 no.1
• /
• pp.1-10
• /
• 2010

Structures under high temperature may have creep behavior and fatigue behavior. Durability study of the structures need the damage analysis with the creep-fatigue effects. In this paper, the damage analysis is studied for a turbine blade in the turbopump for a liquid rocket engine which is operated under high temperature condition. First of all, the load cycle is required for defining the operational characteristics of turbopump. The thermal stress analysis is done for a turbine blade of the turbopump. The stress analysis results are used to judge damage due to the creep and the fatigue. The strain-life method with miner rule is used for fatigue damage analysis. The Larson-Miller parameter master curve and robinson rule are used for the creep damage analysis. The linear damage summation method is used to consider creep-fatigue effects of turbopump turbine. Finally, the analysis results for fatigue and the influence are compared to figure out the damage phenomenon of the turbopump turbine.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.10
• /
• pp.2617-2629
• /
• 1995

The flow through a centrifugal compressor rotor was calculated using the quasi-3-dimensional and fully 3-dimensional Navier-Stokes solution methods. The calculated results, obtained during the development of the computer codes for both methods are discussed. In the inviscid quasi 3-dimensional analysis, stream function formulation was used for the blade to blade (B-B) plane calculations, and the streamline curvature method was used for the meridional (H-S) plane calculations. In the viscous 3-dimensional flow analysis, a control volume method based on a general rotating curvilinear coordinate system was used to solve the time-averaged Navier-Stokes equations, and a standard k-.epsilon. model was used to obtain eddy viscosity. The quasi-3-dimensional analysis reasonably predicts the pressure distributions and requires much less computation time in the region where viscous effects are not strong; however, it fails to predict velocity field and loss mechanism through the impeller passage. The viscous 3-dimensional flow analysis shows reasonable pressure distributions and typical jet-wake flow field through the impeller passage. Secondary flow and total pressure distributions on cross-sectional planes explain the loss mechanisms through the impeller.

• International Journal of Aeronautical and Space Sciences
• /
• v.16 no.2
• /
• pp.295-310
• /
• 2015

In the present study, an unstructured mixed mesh flow solver was used to conduct a numerical prediction of the aerodynamic performance of the S-76 rotor in hover. For the present mixed mesh methodology, the near-body flow domain was modeled by using body-fitted prismatic/tetrahedral cells while Cartesian mesh cells were filled in the off-body region. A high-order accurate weighted essentially non-oscillatory (WENO) scheme was employed to better resolve the flow characteristics in the off-body flow region. An overset mesh technique was adopted to transfer the flow variables between the two different mesh regions, and computations were carried out for three different blade configurations including swept-taper, rectangular, and swept-taper-anhedral tip shapes. The results of the simulation were compared against experimental data, and the computations were also made to investigate the effect of the blade tip Mach number. The detailed flow characteristics were also examined, including the tip-vortex trajectory, vortex core size, and first-passing tip vortex position that depended on the tip shape.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.7
• /
• pp.928-938
• /
• 1997

The end winding is an important part in induction motor for thermal analysis. But there is little information on the heat transfer coefficient of that surfaces because of geometrical complexity. So our experimental object is to know the heat transfer coefficient of end winding and find the optimum design parameter of rotor fan. Carbon coated papers were used for a uniform heat generating surfaces which were easy to fabricate. The experiments of some parameters were performed as varying rotation speed of rotor fan. We obtained the local and average Nusselt number of the end winding surfaces by correcting radiation and conduction losses errors. The results showed that the average Nusselt number increased with rotor fan blade number and width but decreased with end winding length. However, the increasing limits existed in the case of rotor fan width and blade number. So optimum design value were obtained for rotor fan width and blade numbers.