• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1975-1980
• /
• 2004

The three-dimensional flow in a turbine nozzle guide vane passage causes large secondary loss through the passage and increased heat transfer on the blade surface. In order to reduce or control these secondary flows, a linear cascade with a contoured endwall configuration was used and changes in the three-dimensional flow field were analyzed and discussed. Measurements of secondary flow velocity and total pressure loss within the passage have been performed by means of five-hole probes. The investigation was carried out at fixed exit Reynolds number of $4.0{\times}10^5$. The objective of this study is to document the development of the three-dimensional flow in a turbine nozzle guide vane cascade with modified endwall. The results show that the development of passage vortex and cross flow in the cascade composed of one flat and one contoured endwalls are affected by the flow acceleration which occurs in contoured endwall side. The overall loss is reduced near the flat endwall rather than contoured endwall.

• The KSFM Journal of Fluid Machinery
• /
• v.12 no.2
• /
• pp.8-16
• /
• 2009

The objective of this study is to investigate the three-dimensional turbulence flow characteristics of a rotor passage of an one-stage axial flow gas turbine and to investigate the effects of a boundary layer fence installed on the hub endwall of the rotor passage. Secondary flows occurring within the rotor passage (e.g. horseshoe vortex, passage vortex, and cross flow) cause secondary loss and reduce turbine efficiency. To control these secondary flows, a boundary layer fence measuring half the height of the thickness of the inlet boundary layer was installed on the hub endwall of the rotor passage. This study was performed numerically. The results show that the wake and secondary flows generated by the stator reduced the rotor load to constrain the development of cross flow and secondary flow reinforced by the rotor passage. In addition, the secondary vortices occurring within the rotor passage were reduced by the rotation of the rotor. Although, the boundary layer fence induced additional vortices, giving rise to an additional loss of turbine, its presence was shown to reduce the total pressure loss when compared to effects of the case without fence regardless of the relative position of blades by enervating secondary vortices occurred within the rotor passage.

• Journal of computational fluids engineering
• /
• v.8 no.3
• /
• pp.1-6
• /
• 2003

Three-dimensional endwall flow within a linear cascade passage of high performance turbine blade is simulated with a 3-D Wavier-Stokes CFD code (MOSA3D), which is based on body-fitted coordinate system, pressure-correction and finite volume method. the endwall flow characteristics, including the development and generation of horseshoe vortex, passage vortex, etc. are clearly simulated, consistent with the generally known tendency The effects of both turbulence model and convective differencing scheme on the Prediction performance of endwall flow are systematically analyzed in the present paper. The convective scheme is found to have stronger effect than the turbulence modei on the prediction performance of endwall flow. The present simulation result also indicates that the suction leg of the horseshoe vortex continues on the suction side until it reaches the trailing edge.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.956-961
• /
• 2003

Direct numerical simulations of flow over a circular cylinder are performed at two different Reynolds numbers (Re=220 and 300) that correspond to three-dimensional instabilities of mode A and mode B, respectively, to investigate the characteristics of drag and lift at these Reynolds numbers. The drag and lift coefficients are measured locally along the spanwise direction and their characteristics are studied in detail. The variation of total drag in time is large at Re=220, and the total drag becomes minimum when vortex dislocation occurs in the wake. The drag and lift variations in space are also closely associated with the evolution of vortex dislocation at this Reynolds number. At Re=300, vortex dislocation is not found in the wake and temporal variations of drag and lift are much smaller than those at Re=220, but their spatial variations are quite large due to the near-wake secondary vortices existing in the mode B instability.

• International Journal of Aeronautical and Space Sciences
• /
• v.11 no.4
• /
• pp.319-325
• /
• 2010

For decades, researchers have rigorously studied the characteristics of flow traveling around blunt objects in order to gain greater understanding of the flow around aircraft, vehicles or vessels. Many different types of flow exist, such as boundary layer flow, flow separation, laminar and turbulent flow, vortex and vortex shedding; such types are especially observed around circular cylinders. Vortex shedding around a circular cylinder exhibits a two-dimensional flow structure possessing a Reynolds number within the range of 47 and 180. As the Reynolds number increases, the Karman vortex changes into a three-dimensional flow structure. In this paper, a numerical analysis was performed examining the flow and aero-acoustic field characteristics around a circular cylinder using an optimized high-order compact scheme, which is a high order scheme. The analysis was conducted with a Reynolds number ranging between 300 and 1,000, which belongs to B-mode flow around a circular cylinder. For a B-mode Reynolds number, a proper spanwise length is analyzed in order to obtain the characteristics of three-dimensional flow. The numerical results of the Strouhal number as well as the lift and drag coefficients according to Reynolds numbers are coincident with the other experimental results. Basic research has been conducted studying the effects an unstable three-dimensional wake flow on an aero-acoustic field.

• The KSFM Journal of Fluid Machinery
• /
• v.7 no.5 s.26
• /
• pp.36-42
• /
• 2004

The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1389-1394
• /
• 2004

Experiments were done for the unsteady flow in a counter rotating axial flow fan near peak efficiency and stall point. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional passage flow patterns were investigated through the acquired data by the $45^{\circ}$ inclined hot-wire. Comparison of flow characteristics between two different operating conditions such as tip vortex, secondary flow and turbulence intensity were performed through the analyses of axial, radial and tangential velocity distributions. As a result, tip vortex and secondary flows are enforced and measured obviously at stall point.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.257-265
• /
• 2009

The present study deals with the leading edge shape on a wing-body junction to decrease a horseshoe vortex, one of the main factors to generate the secondary flow losses. The shape of leading-edge is optimized with design variables form the leading-edge shape. Approximate optimization design method is used for the optimization. The study is investigated using $FLUENT^{TM}$ and $iSIGHT^{TM}$. As the result, total pressure coefficient of the optimized design case was decreased about 9.79% compare to the baseline case.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.371-374
• /
• 2006

The objective of this study is to determine the influence of free-stream turbulent intensity on the three-dimensional turbulent flow in a linear turbine cascade. The range of free-stream turbulence intensity considered is 0.7~10%. This study was performed numerically. The results show that the mass averaged loss coefficient increased according to the increase of free-stream turbulence intensity due to increased value of the mass averaged total pressure loss coefficient which was higher than the decreased value of the mass averaged secondary flow loss coefficient. The loss coefficient distribution was changed suddenly at a free-stream turbulence intensity of 10% while the loss coefficient distribution was rarely changed at a lower free-stream turbulence intensity of 5%.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.08a
• /
• pp.171-175
• /
• 2003

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages is carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry is accurately modeled adopting the embedded H grid topology. An explicit four-stage Runge-Kutta scheme is used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, are interpreted and compared with the experimental data from the Penn State turbine stage. Good agreement between the experimental data and the numerical prediction was achieved in the sense of the major features of the flow fields.