[en] Experiments were conducted in a low speed stationary annular cascade to investigate local heat transfer characteristics on the tip and shroud and the effect of inlet Reynolds number on the tip and shroud heat transfer. Detailed mass transfer coefficients on the blade tip and the shroud were obtained using a naphthalene sublimation technique. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about 2.5% of the blade chord. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from 1.0x10⁵ to 2.3x0⁵ to investigate the effect of Reynolds number. Flow reattachment after the recirculation near the pressure side edge dominates the heat transfer on the tip surface. Shroud surface has very intricate heat/mass transfer distributions due to complex flow patterns such as acceleration, relaminarization, transition to turbulent flow and tip leakage vortex. Heat/mass transfer coefficient on the blade tip is about 1.7 times as high as that on the shroud or blade surface. Overall averaged heat/mass transfer coefficients on the tip and shroud are proportional to Re_c^0.65 and Re_c^0.71, respectively

[en] For the extensive investigation of local heat/mass transfer on the near-tip surface of turbine blade, experiments were conducted in a low speed stationary annular cascade. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about 2.5% of the blade chord. Detailed mass transfer coefficient on the blade near-tip surface was obtained using a naphthalene sublimation technique. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from 1.0x10⁵ to 2.3x10⁵. Extremely complex heat transfer characteristics are observed on the blade surface due to complicated flow patterns, such as flow acceleration, laminarization, transition, separation bubble and tip leakage flow. Especially, the suction side surface of the blade has higher heat/mass transfer coefficients and more complex distribution than the pressure side surface, which is related to the leakage flow. For all the tested Reynolds numbers, the heat/mass transfer characteristics on the turbine blade are the similar. The overall averaged Sh_c values are proportional to Re_c^0.5 on the stagnation region and the laminar flow region such as the pressure side surface. However, since the flow is fully turbulent in the near-tip region, the heat/mass transfer coefficients are proportional to Re_c^0.8

[en] The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud for the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to 1.5x10⁵. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation

[en] In the present study, the effect of blade rotation on blade heat transfer is investigated by comparing with the heat transfer results for the stationary blade. The experiments are conducted in a low speed annular cascade with a single stage turbine and the turbine stage is composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has a flat tip and the mean tip clearance is 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. For the experiments, the inlet Reynolds number is Re_c=1.5x10⁵, which results in the blade rotation speed of 255.8 rpm. Blade rotation induces a relative motion between the blade and the shroud as well as a periodic variation of incoming flow. Therefore, different heat/mass transfer patterns are observed on the rotating blade, especially near the tip and on the tip. The relative motion reduces the tip leakage flow through the tip gap, which results in the reduction of the tip heat transfer. However, the effect of the tip leakage flow on the blade surface is increased because the tip leakage vortex is formed closer to the surface than the stationary case. The overall heat/mass transfer on the shroud is not affected much by the blade rotation

[en] The present study investigates the convective heat/mass transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The internal cooling passage is simulated using a square duct with Λ -and V-shaped rectangular ribs which have a 60 .deg. attack angle. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall. The secondary flow patterns and the local heat transfer in the duct are changed significantly according to the rib orientation. A square duct with Λ -and V-shaped ribs have two pairs of secondary flow due to the rib arrangement. Therefore, the average heat/mass transfer coefficients and pressure drop of Λ -and V-shaped ribs are higher than those of the continuous ribs with 90 deg. and 60 .deg. attack angles. The Λ -shaped ribs have higher heat/mass transfer coefficients than the V-shaped ribs, and the uniformity of heat/mass transfer coefficient are increased with the discrete ribs due to the flow leakage and acceleration near the surface

[en] An experimental study has been conducted to investigate the film cooling performances for two and three staggered rows of the rectangular-shaped film cooling holes with various blowing rates. Three different cooling hole shapes such as a straight rectangular hole, a rectangular hole with laterally expanded exit, a circular hole are tested. The rectangular cross-section has the aspect ratio of 2 at the hole inlet with the hydraulic diameter of 10 mm. The area ratio of the exit to the hole inlet is 1.8 for the rectangular hole with expanded exit. The holes are spaced 3d apart in the spanwise direction and 4d apart in the streamwise direction with staggered arrangement. The results show that the rectangular-shaped holes provide better performance than the cylindrical holes because the penetration of coolant is reduced and the lateral spreading of coolant is promoted. For rows of film cooling holes, the film cooling performance is decreased with increasing blowing rate

[en] Two Perforated Plates are used to investigate local heat/mass transfer characteristics in an impingement/diffusion cooling system. A naphthalene sublimation method is conducted to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. Two plates are placed in parallel position with gap distances of 1, 2, 4, and 6 times of effusion hole diameter. The effects of hole arrangements of the plates are studied for staggered ,square, and hexagonal arrays. The experiments are conducted at Reynolds number of 10,000 based on the effusion hole diameter. The results show that the smaller hole size in the staggered array has the higher momentum flows through the impingement holes. In the square array, heat/mass transfer coefficients are obtained for the hexagonal array

[en] 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.deg 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 di sapper 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 turning and the rotation

[en] Two perforated plates are used to investigate local heat/mass transfer characteristics in an impingement/effusion cooling system. A naphthalene sublimation method is conducted to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. The two plates are placed in parallel position with gap distances of 1, 2, 4 and 6 times of effusion hole diameter. The effects of hole arrangements of the plates are studied for staggered, square, and hexagonal arrays. The experiments are conducted at Reynolds number of 10,000 based on the effusion hole diameter. The results show that the smaller hole size in the staggered array has the higher transfer coefficients on the stagnation region due to the formation of higher momentum flows through the impingement holes. In the square array, heat/mass transfer on the target plate is more uniform as the number of impingement holes increases. High and uniform heat/mass transfer coefficients are obtained in the hexagonal array

[en] Impingement/effusion cooling technique is used for combustor liner or turbine parts cooling in gas turbine engine. In the impingement/effusion cooling system, the crossflow generated in the cooling channel induces an adverse effect on the cooling performance, which consequently affects the durability of the cooling system. In the present study, to reduce the adverse effect of the crossflow and improve the cooling performance, circular pin fins are installed in impingement/effusion cooling system and the heat transfer characteristics are investigated. The pin fins are installed between two perforated plates and the crossflow passes between these two plates. A blowing ratio is changed from 0.5 to 1.5 for the fixed jet Reynolds number of 10,000 and five circular pin fin arrangements are considered in this study. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The results show that local distributions of heat/mass transfer coefficient are changed due to the installation of pin fins. Due to the generation of vortex and wake by the pin fin, locally low heat/mass transfer regions are reduced. Moreover, the pin fin prevents the wall jet from being swept away, resulting in the increase of heat/mass transfer. When the pin fin is installed in front of the impinging jet, the blockage effect on the crossflow enhances the heat/mass transfer. However, the pin fin installed just behind the impinging jet blocks up the wall jet, decreasing the heat/mass transfer. As the blowing ratio increases, the pin fins lead to the higher Sh value compared to the case without pin fins, inducing 16%∼22% enhancement of overall Sh value at high blowing ratio of M=1.5