Jin Taek Chung

Effect of Triangular Grooved Tip on Blade Tip Region Heat Transfer

A numerical analysis was conducted to investigate the effect of the triangular grooved tip shape on the flow and heat transfer characteristics near the tip region. To study the effect of the triangular grooved tip shape, five triangular grooved tips were designed by changing the relative apex location of the triangular groove. Numerical computations were conducted for a total of six tip shapes, including a squealer tip. The contour plot of the secondary velocity and streamline were analyzed to understand the flow over a blade tip in detail, and the effect of the leakage vortex was discussed by comparing the total pressure loss. To compare the heat transfer characteristics, the Nusselt number and heat load over the tip surface, including the cavity sidewall, were analyzed. Results showed that the origin and trace of the vortex in the tip cavity depended on the apex location of the triangular groove, and because of this, the Nusselt number on the tip and blade suction side surface were also affected. Among ...

Effect of Inlet Velocity Profile on Heat Transfer in a Rotating Channel

The effects of the inlet velocity profile on the heat transfer coefficient in rotating smooth and angle ribbed channels were experimentally investigated. The detailed heat transfer coefficient was measured using the transient liquid crystal technique. Reynolds numbers based on the channel hydraulic diameter of 10,000, 20,000, and 30,000 were tested, and the corresponding rotation number ranged from 0.067 to 0.184. Results showed that the Nusselt number ratio decreased as the Reynolds number increased for both channel cases, and the Nusselt number for the trailing surface is the highest for both channel cases. For the smooth channel case, the Nusselt number for the leading surface is higher than that for the stationary surface, while the reverse trend was observed for the ribbed channel. An inlet velocity profile with a higher centerline velocity resulted in higher heat transfer for the smooth channel, but the skewed inlet velocity profile caused higher heat transfer for the ribbed channel.

Heat transfer and secondary flow with a multicavity gas turbine blade tip

Multicavity gas turbine blade tips were formed by adding ribs in the blade tip cavities of squealer tips, and the effects of the tip clearance size, the number and the installation angle of the ribs on the tip heat transfer, and the blade passage total pressure loss were investigated experimentally. Tests were conducted in a low-speed linear cascade. The transient liquid crystal technique and a seven-hole probe were used to measure the heat transfer and flowfield, respectively. Results showed that a multicavity tip was able to reduce the total pressure loss coefficient, and the total pressure loss coefficients decreased as the number of ribs increased. Additional ribs on the tip cavity reduced the heat transfer coefficients on the cavity surface near the leading edge, but induced an additional high heat transfer coefficient region downstream from the rib due to the flow reattachment.

Aerodynamic Design and Numerical Study of a Propane-Refrigerant Centrifugal Compressor for LNG Plant

Key Words: Aerodynamic Design(공력설계), Centrifugal Compressor(원심압축기), Tip Clearance(익단간극),CFD(전산유체역학), Propane Refrigerant(프로판냉매), LNG Plant(LNG 플랜트)초록: 본연구에서는4단으로구성된LNG 플랜트용프로판냉매원심압축기각단의설계점에대해상용코드를이용하여공력설계를하였다. 1차원공력설계결과와3차원유로형상의타당성은유동해석을통해확인하였다. 특히입구전압이높고회전수가큰4단압축기임펠러의유로와베인리스디퓨저내부유동에대한속도장, 압력장및엔트로피등의유동특성에대해고찰하였고, 아울러익단간극이유동장에미치는영향에대해서도알아보았다. 본연구결과는프로판냉매압축기의시스템제작에활용될것이며추후실제실험결과와비교하고자한다. 향후설계된프로판냉매압축기에대한LNG 플랜트에서의실증시험을통해구체적인설계결과에대한평가및설계개선이이루어지리라생각한다.Abstract: We design a four-stage propane-refrigerant centrifugal compressor for an LNG plant. Using a commercialcode, we aerodynamically designed the compressor at each design point of the corresponding stages. We estimated theone-dimensional aerodynamic design output and the three-dimensional shape of the impeller flow passage viathree-dimensional flow analysis. In particular, we discuss in detail the flow characteristics of the impeller and thevaneless diffuser passages of the fourth-stage compressor in terms of the velocity fields, the pressure, and the entropydistributions of the flow passages. We include the flow effects of the tip clearance flow, because at this stage therotating speed and total inlet pressure are higher than those at the other compressor stages are. We carried outperformance tests of the designed compressor stages using propane as a refrigerant in the LNG cycle. The practicalevaluation could lead to design enhancements in the future.

Numerical Study of Aerodynamics of Turbine Rotor with Leading Edge Modification Near Hub

Key Words: Gas Turbine(가스터빈), Aerodynamic Efficiency(공력효율), Rotor(동익), Leading Edge(선단),Modification(수정), Hub(허브), Bulbous Design(구륜형상)초록: 이논문은터빈로터의형상변화에따른공력특성에대하여분석하였다. 본논문의터빈은헬리콥터의보조동력장치로사용되는소형엔진이다. 소형엔진은팁형상의구조적취약성때문에성능을향상시키기어렵다. 그러므로, 터빈의허브를개선하는것이여러가지측면에서유리하다. 터빈의작동유체는고온고압의가스이다. 터빈표면의열전달률이고려되었을때, 열부하에의한블레이드의손상을줄이기위해서는블레이드표면의열전달률분포를고찰하여야한다. 수치모사결과를검증용실험값과비교하였을때, SST난류모델은공력특성을잘반영하고열전달예측성능도우수하였다. 결론적으로, 허브측선단에서구륜설계(bulbous design)를적용하였을때공력효율이향상되었고, 전체공력손실중끝벽손실은15% 감소되었다.Abstract: This study aims to analyze the aerodynamics when the geometry of the turbine rotor is modified. Theturbine used in this study is a small engine used in the APU of a helicopter. It is difficult to improve theperformance of small engines owing to the structural weakness of the blade tip. Therefore, the improvement of thehub geometry is investigated in many ways. The working fluid of a turbine is a high-temperature and high-pressuregas. The heat transfer rate of the turbine surface should be considered to avoid the destruction of blade owing to theheat load. The SST turbulence model gives an excellent prediction of the aerodynamic behavior and heat transfercharacteristics when the numerical simulations are compared with the experimental results. In conclusion, theaerodynamic efficiency is improved when a bulbous design is applied to the leading edge near the hub. The endwallloss is reduced by 15%.

Measurement of Blade Tip Heat Transfer and Leakage Flow in a Turbine Cascade With a Multi-Cavity Squealer Tip

Tip leakage flow induces high heat transfer to the blade tip and causes significant aerodynamic losses. In this paper, we propose a multi-cavity squealer tip with an additional rib in the squealer cavity. Our study investigated the effects of the rib location and shape on the blade tip heat transfer and the total pressure loss. Experiments were performed in a five-bladed linear cascade using a low speed wind tunnel. The blade chord, pitch, and span length were 126mm, 102.7mm, and 160mm, respectively. The Reynolds number, based on the blade chord and cascade exit velocity, was 2.44×105, and a tip clearance of 1.25% of the blade span was considered. The additional rib was installed in the squealer tip cavity near the leading edge, the mid-chord, and the training edge, respectively. The shape of the rib was also varied from rectangular to triangular in order to minimize the rib surface area exposed to the hot gas. The secondary flow and total pressure loss were measured using a seven-hole probe at one-chord downstream of the blade trailing edge, and the heat transfer coefficient distributions were measured by utilizing the hue-detection based transient liquid crystal technique. Flow measurement results indicated that the proposed multi-cavity tip reduced the total pressure loss. The blade tip heat transfer measurement results showed that the proposed multi-cavity tip was able to reduce the maximum heat transfer region near the cavity floor near the leading edge, but the heat transfer on the second cavity floor increased due to the leakage flow reattachment.Copyright