As the gas turbine becomes smaller and is operated at high altitude, the aerodynamic condition frequently lies at the low Reynolds number. In the present study, three-dimensional computations were performed to understand the effects of the low Reynolds number on the loss characteristics in an axial compressor. The numerical results showed that the performance of the axial compressor like the static pressure rise is reduced by the full-span separation on the suction surface and the boundary layer on the hub, caused by the low Reynolds number. Compared with that at the reference Reynolds number, the total pressure loss at the low Reynolds number was found to be greater from the hub to 85 per cent span and smaller above the 85 per cent span. For a detailed analysis, the total pressure loss was scrutinized through three major loss categories available in the subsonic axial compressor: profile loss, tip leakage loss, and endwall loss.
It is known that tip clearance flows reduce the pressure rise, flow range and efficiency of turbomachinery. So, a clear understanding about flow fields in the tip region is needed to efficiently design the turbomachinery. In the present paper, the Navier-Stokes code with the proper treatment of the boundary conditions has been developed to analyze the threedimensional steady viscous flow fields in the transonic rotating blades and a numerical study has been conducted to investigate the detailed flow physics in the tip region of transonic rotor, NASA Rotor 67. The computational results in the tip region of transonic rotor show the leakage vortices, leakage flow from pressure side to suction side and their interaction with a shock. Depending on the operating conditions, load distributions and the position of shock-wave on the blade surface are very different close to the blade tip of transonic compressor rotor. It is shown that the load distribution and the shock-wave position close to blade tip have great effects on the starting position of leakage vortex and direction of leakage flow. peak efficiency Experiment Calculation choke J I L j L j Ι-Ο.92 0.94 0.96 0.98 Mass flow rate/Mass flow rate at choke 1 ιnear stall Experiment Calculation J I L. J ' ' J_ J I L 0.92 0.94 0.96 0.98
A 3D numerical simulation was conducted to study the effect of inlet boundary layer thickness on rotating stall in an axial compressor. The inlet boundary layer thickness had significant effects on the hub-corner-separation at the corner of hub and suction surfaces. The hub-corner-separation grew considerably for a thick inlet boundary layer as the load increased, while it diminished to become indistinguishable from the rotor wake for a thin inlet boundary layer and another corner-separation originated near the casing. This difference in the internal flow near stall also had a large effect on characteristics of the rotating stall, especially the initial asymmetric disturbance and the size of stall cells. While a prestall disturbance arises firstly in the hub-corner-separation for the thick inlet boundary layer, an asymmetric disturbance was initially generated in the tip region because of the corner-separation for the thin inlet boundary layer. This disturbance was transferred to the tip leakage flow and grew to become an attached stall cell, which adheres to the blade passage and rotates at the same speed as the rotor. When this attached stall cell reached a critical size, it started moving along the blade row and became a short-length-scale rotating stall. The size of the stall cell for the thick inlet boundary layer was larger than for the thin inlet boundary layer. Due to the bigger size of the stall cell, the performance of the single rotor for the former case dropped more significantly than for the latter case.
A three-dimensional unsteady flow simulation was conducted to investigate the relation of clocking effect and secondary flow in a 1.5 stage axial turbine. Six relative positions of two stator rows were investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% was obtained depending on clocking positions. However, internal flows had some different features from the previous study at maximum and minimum efficiency positions, since the first stator wake was mixed out with the rotor wake before arriving at the leading edge of the second stator at mid-span. Instead of the first stator wake, it was found that the secondary flow plays an important role to the efficiency variation at each clocking position. The time-averaged local efficiency along the span at maximum efficiency was more uniform than that at minimum efficiency. That is, the span-wise efficiency distribution at minimum efficiency has larger values at mid-span but smaller values near the hub and casing compared with the case at maximum efficiency. This spanwise efficiency distribution could be also explained by secondary flow behavior in an axial turbine.
서 론산업 The numerical simulation has been performed to predict the performance of the fire suppression system for cabin of shipboard enclosure. The present study aims ultimately at finding the optimal parametric conditions of the mist-injecting nozzles using the CFD methods. The open numerical code was used for the present simulation named as FDS (Fire Dynamics Simulator). Application has been done to predict the interaction between water mist and fire plume. In this study, the passenger cabin was chosen as simulation space. The computational domains for simulation in the passenger
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