Jun Su Park

Heat Transfer in Rotating Channel With Inclined Pin-Fins

This study is to examine experimentally the effects of pin inclination and pin height-to-diameter ratio on the heat/mass transfer characteristics in a pin-fin channel with and without rotation. The test model consists of staggered pin-fin arrays with an interpin spacing of 2.5 times of the pin-diameter (S/D = 2.5) in both longitudinal and transverse directions. Detailed local heat/mass transfer coefficients on the two principal surfaces of rotating channel are measured using the naphthalene sublimation technique. The inclined angles (θ) studied are 60 deg and 90 deg. The pin height-to-diameter ratio (H p /D p ) ranges from 2 to 4. The Reynolds number is fixed at 7.0 × 10 3 with two rotation numbers (0.0 and 0.2). The measured data show that the overall array heat/mass transfer decreases with the angle of inclination relative to the vertical orientation. The overall array averaged as well as the row-resolved heat/mass transfer increases with an increase in H p /D p . Rotation generally results in higher heat/mass transfer than the corresponding stationary case. The nonuniformity or redistribution of heat/mass transfer induced by the Coriolis force generally perceived in a ribbed or smooth channel is less evident in a pin-fin channel.

Trailing Edge Cooling of a Gas Turbine Blade With Perforated Blockages With Inclined Holes

We propose an improved hole array to enhance the cooling performance of a perforated blockage. The internal passage in the trailing region of the blade was modeled as a wide square channel with three parallel blockages. Various configurations of perforated blockages were tested with a fixed Reynolds number. The baseline design had holes positioned along the centerline of the blockage in the lateral direction, and the array pattern, hole size, and hole direction were manipulated to enhance the cooling performance. Experiments were performed to obtain information on heat transfer and pressure loss. A naphthalene sublimation method was adopted to obtain detailed heat transfer distributions on the surfaces, using the correlation between heat and mass transfer. The pressure was measured at several points to evaluate the pressure loss. The proposed inclined hole array showed noticeably improved cooling performance, as much as 50% higher than the conventional configuration.Copyright

Heat transfer on rotating channel with various heights of pin-fin

Pin-fins have been used to enhance the heat transfer near the trailing edge of a turbine airfoil. Previous pin-fin heat transfer studies focused mainly on the array geometry of pin height-to-diameter equal to unity in a stationary frame. This study experimentally examines the effects of pin height-to-diameter ratio (Hp /Dp ) from 2 to 4 and rotation number (Ro ) from 0 to 0.2. The tested model used a staggered pin-fin array with an inter-pin spacing of 2.5 times the pin-diameter (S/D = 2.5) in both longitudinal and transverse directions. Detailed heat/mass transfer coefficients were measured using the naphthalene sublimation technique with a heat-mass transfer analogy. The data measured suggest that an increase in Hp /Dp increases the level of array heat/mass transfer. Array averaged Sherwood numbers for Hp /Dp = 3 and Hp /Dp = 4 are approximately 10% and 35% higher than that of Hp /Dp = 2. The effect of rotation induces notable difference in heat/mass transfer between the leading surface and the trailing surface. The heat transfer coefficients change a little although the rotating number increases in the tested range because the pin-fins break the rotation-induced vortices.Copyright

Effect of Unsteady Wakes on Local Heat Transer of 1st Stage Blade Endwall

We investigated the local heat and mass transfer on the endwall surface at different Strouhal numbers. The Strouhal number represents the interaction between the turbine stator and rotor. Thus, characteristics of flow and heat transfer on the endwall surface change for different Strouhal numbers. The experiment was performed in five-bladed linear cascade blades with moving cylindrical rods simulating unsteady wakes effects. The Reynolds number which was based on the blade cord length and inlet velocity was 100,000. The range of the Strouhal number varies from 0 to 0.22 to investigate the effect of unsteady wakes on the endwall surface. The local heat and mass transfer were measured on the endwall surface using the naphthalene sublimation method. The results showed that the local heat transfer characteristics changed depending on the Strouhal number. In the steady case, the occurrence of a horseshoe vortex, passage vortex and corner vortex caused non-uniform heat transfer on the endwall surface. However, in the unsteady case, the unsteady wake effect caused more uniform heat transfer on the endwall surface. As the Strouhal number increased, heat transfer increased and became more uniform compared with the steady case. Thus, an appropriate cooling system is necessary for stator and rotor endwalls in situations of real gas turbine operation.© 2015 ASME

Effects of an Unsteady Wake on Heat Transfer of Endwall Surface in the Linear Cascade

The present study aimed to investigate the effect of an unsteady wake on the heat transfer for the endwall surface of a linear turbine blade cascade. A naphthalene sublimation method was implemented to obtain the detailed heat/mass transfer distributions on the endwall surface. Tests were conducted on a five-passage linear cascade in a low-speed wind tunnel. The effects of unsteady wakes were simulated in the facility by a wake generator consisting of circular rods that were traversed across the inlet flow. The test conditions were fixed at a Reynolds number of 70,000 based on the inlet velocity and chord length. The flow coefficients were varied from 1.3 to 4.2. and range of Strouhal number was 0.1 to 0.3. The results showed that the heat transfer distributions differed between steady and unsteady test cases. The overall heat transfer for the unsteady test cases was higher, and the heat transfer was enhanced with increasing the Strouhal number due to the resulting thin boundary layer and high turbulence intensity. Therefore, a cooling system for the endwall of a rotor should focus on decreasing the high temperatures of the endwall surface induced by the unsteady wakes.Copyright

Heat Transfer and Effectiveness on the Film Cooled Tip and Inner Rim Surfaces of a Turbine Blade

Detailed heat/mass transfer coefficients and film-cooling effectiveness were measured on the tip and inner rim surfaces of a rotor blade with a squealer rim. The blade was a two-dimensional version of a modern first-stage gas turbine rotor blade with a squealer rim. The experimental apparatus was equipped with a linear cascade of three blades, the axial chord length (Cx ) of which was 237 mm with a turning angle of 126°. The mainstream Reynolds number based on the axial chord was 1.5×105 . The turbulence intensity level at the cascade inlet was approximately 12%. Measurements were made at three different rim heights (H) of about 3%, 6%, and 9% of the axial chord length. The tip clearance (C) ranges were 1–3% of the axial chord length. Also, three different types of blade tip surfaces were equipped with a single row of film-cooling holes along the camber line, near the pressure and the suction side rim. In particular, a coolant was injected at an incline of 45° from near the suction side film cooling holes. The film cooling experiments were done with a fixed tip clearance and rim height at 1% and 6% of the axial chord length. The blowing rate was fixed at 1.5. High heat transfer rates were observed near the leading edge on the tip surface in some cases, due to the reattachment of tip leakage flow. The peak values moved toward the suction-side edge, and the magnitude and area of high heat transfer increased near the leading edge as the tip clearance increased. The heat transfer decreased on the tip surface with increases in the rim height. In the film-cooling cases, the high heat transfer and film-cooling effectiveness region appeared near the film-cooling holes.© 2010 ASME

Heat/Mass Transfer Measurement on The Tip Surface Of Rotor Blade With Squlear Rim

The present study investigates local heat/mass transfer characteristics on blade tip surface with squealer rim. A linear cascade experimental setup consists of three large scale airfoils was used. The axial chord length and turning angle of test blade are 237 mm and 126°, respectively. Heat/mass transfer coefficients were measured with three different rim heights (3%, 6% and 9% of axial chord length) and fixed tip clearance (2% of axial chord length). Main flow Reynolds number based on axial chord length is 1.5×105. Naphthalene sublimation method is used to measure the detailed mass transfer coefficient on the blade tip surface. The heat/mass transfer results show that as the rim height increases, the peak values on the upstream region of the tip surface decreases and moves to the suction side rim. At the downstream region of the tip surface, the pitch‐wise averaged heat/mass transfer coefficients increases as the rim height increases.

Local Heat and Mass Transfer Characteristics for Multi-Layered Impingement/Effusion Cooling

Multi-layered impingement/effusion cooling is an advanced cooling configuration that combines impingement jet cooling, pin cooling, and effusion cooling. The arrangement of the pins is a critical design factor because of the complex heat transfer in the internal structure. Therefore, it is important to measure the local heat transfer at all internal surfaces as a function of the pin spacing. In this study, a naphthalene sublimation method was employed to measure the details of the heat/mass transfer at the internal surfaces, including the injection plate, effusion plates, and the pins. An staggered array of holes was formed at the injection plate and effusion plates where the ratio of the height to the diameter of the pins, h/d, was fixed at 0.25. The ratio of the pin spacing to the diameter, sp/d, was varied in the range 1.5≤sp/d≤6, and the Reynolds number based on the hole diameter was 3000. As a result, a vortex ring formed near the pin, leading to re-impingement flows in the narrow channel. The jet flow impinged strongly on the pin, resulting in a large heat transfer region at each surface. The total average Sherwood number with sp/d=1.5 was larger than that with sp/d=6 by a factor of 1.5.Copyright

Augmented Heat Transfer for Angled Rib With Intersecting Rib in Rectangular Channels of Different Aspect Ratios

This study was an experimental investigation of the effect of an intersecting rib on heat/mass transfer performance in rectangular channels with angled ribs and different aspect ratios. In a rib-roughened channel with angled ribs, heat/mass transfer performance deteriorates as the channel aspect ratio increases, since the vortices induced by angled ribs diminish with increasing aspect ratio. A longitudinal rib that bisects the angled ribs is suggested to overcome this disadvantage. The heat transfer performance of angled rib configurations with a 60° attack angle were tested with and without an intersecting rib using naphthalene sublimation method. The channel aspect ratio is varied from 1 to 4. When the intersecting rib was present, additional vortices were generated at every point of intersection with the angled ribs. Thus the heat/mass transfer performance was significantly enhanced for all channel aspect ratios when an intersecting rib was added to an ordinary angled rib configuration.Copyright

Total cooling effectiveness on laminated multilayer for impingement/effusion cooling system

The next generation aircraft combustor liner will be operating in more severe conditions. This means that the current cooling system needs significant amounts of cooling air to maintain cooling intensity. The present study investigates experimentally the total cooling effectiveness of an integrated impingement/effusion cooling system (thin perforated laminate plate) and effusion cooling system (single plate) at the same blowing ratio of 0.2 to 1.2. The infrared thermography method was employed to evaluate total cooling effectiveness and to determine the fully developed region of cooling performance. The holes arrays on both plates are 13 × 13 and the centers formed a square pattern (i.e., an in-line array). The perforated laminate plate is constructed of three layers and pins that were installed between the layers. In order to avoid increasing the thickness and volume, the layer thickness-to-hole diameter ratio was 0.29, and the pin height-to-hole diameter ratio, which is equivalent to the gap between the plates, was 0.21. The single plate had the same total plate thickness-to-hole diameter, but was composed of only one layer. As a result, the total cooling effectiveness of the laminate plate is 47% ∼ 141% better than single plate depending on the blowing ratio. Also, a fully developed region appears on the 2nd or 3th row of holes.Copyright