Heeyoon Chung

Heat Transfer and Fluid Flow on Dimpled Surface With Bleed Flow

This study investigates the effects of bleed flow on heat transfer and fluid flow on a dimpled surface in a rectangular channel. The heat transfer on a dimpled surface with bleed flow is compared with that on a dimpled surface without bleed flow. The height of the channel is 15.0 mm. The dimples are arrayed in staggered on the bottom surface of the channel with a pitch of 15.0 mm. The dimple depth is 3.75 mm and the dimple footprint diameter is 13.0 mm. The bleed hole is installed on the inner surface of the dimple and the diameter of the hole is 1.3 mm. The tests were conducted with varying Reynolds numbers from 1000 to 10,000 and 0.5% of total mass flow is flowing out through a bleed hole. A numerical method was employed to determine the detailed heat transfer coefficients. Commercial computational fluid dynamics software, ANSYS CFX 13.0, is adopted and the Shear Stress Transport model is set to turbulent model. As a result, the overall heat transfer rate on dimpled surface with bleed flow is 10–20% higher than that without bleed flow.

Effect of various rib arrangements on heat transfer in a semicylinder channel with effusion flow

ABSTRACT The flow and heat transfer characteristics of various rib configurations on a concave channel surface with effusion holes were investigated. A semicylindrical channel with three rows of effusion holes was used to simplify the blade leading edge and eight kinds of ribs were attached on the internal concave surface for comparison. Continuous and broken ribs were both applied at 90°, as were upstream-pointed V-shaped and downstream-pointed V-shaped ribs. The Reynolds-averaged Navier–Stokes equation was solved using commercial software. The result included the divided-area-averaged and local Nusselt number distribution; the overall average Nusselt number on the concave surface is also discussed.

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

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

Effect of Manufacturing Tolerances on the Cooling Performance of Internal Rib Turbulated Passages

ABSTRACT The manufacturing tolerances of rib turbulators lead to variations in the cooling of internal ribbed passages because the manufacturing tolerances cause the actual geometry to differ some from the design which affects the flow structure as well as the coolant mass flow rate. Such variations may significantly affect the system cooling performance, and may lead to the failure of hot components. Thus, it is necessary to determine the effects of manufacturing tolerances on the cooling performance for such variations in rib turbulators in internal passages. This study numerically investigates the cooling of internal rib turbulated passages using the relationship between the geometric parameters and the coolant mass flow rate using the three-dimensional Reynolds-averaged Navier–Stokes equations for various rib heights, rib widths, wall thicknesses, and coolant mass flow rates. Correlations are developed to predict the cooling performance in response to geometric variations of the internal passages due to manufacturing tolerances. The variations in the design parameters of the internal rib turbulated cooling system has differing effects on the cooling performance, even within the same range of manufacturing tolerances.

Conjugate Heat Transfer on Full-Coverage Film Cooling With Array Impingement Jets

We report an investigation of the total cooling effectiveness of a film cooled surface with staggered array impingement jet cooling using infra-red thermography. Heat transfer experiments were carried out using three film cooled test plates of different thermal conductivities: stainless steel (with a thermal conductivity, k = 13.4 W/mK), Corian® (k = 1 W/mK), and polycarbonate (k = 0.2 W/mK). The effects of conduction through the test plates and convective heat transfer due to the arrayed impingement jets were analyzed. The inclination angle of the film cooling holes was 35° and that of the impingement jet holes was 90°. The film and impingement jet holes on each plate were arranged in a staggered pattern, and the film cooling holes and impingement jet holes were also positioned in a staggered pattern. The jet Reynolds number based on the hole diameter was Rejet = 3,000 and the equivalent blowing rate was M = 0.3. The ratio of the target surface height to the hole diameter was varied in the range 1 < H/d < 5. The diameter of both the film cooling holes and impingement jet holes was 5 mm. The total cooling effectiveness was investigated with and without the impingement jets. When the impingement jets were added to the internal cooling, the averaged total cooling effectiveness was enhanced about 8.4%. The stainless steel plate was found to exhibit better cooling performance with more uniform temperature distribution. The total cooling effectiveness was increased up to 0.87 in the stainless steel plate, and the maximum deviation of total cooling effectiveness in the stainless steel was reduced to 85% from that in polycarbonate plate along the lateral direction. The total cooling effectiveness was related to the Biot number of the film cooled plate, however, the effect of the H/d ratio was not significant.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

Effect of Secondary Flow Direction on Film Cooling Effectiveness

Key Words: Double-jet Film Cooling(이중분사 막냉각), Secondary Flow Channel(이차유로), Film CoolingEffectiveness(막냉각효율), Anti-Kidney Vortex(안티키드니와류), Numerical Analysis(수치해석)초록: 막냉각에관한많은연구들은주유동과이차유로가평행한형태로연구가이루어졌다. 하지만실제터빈블레이드에서이차유로의방향은일반적으로주유동의방향에수직한형태이다. 그래서본연구에서는이차유동의방향이이중분사막냉각의효율에미치는영향을수치해석을통해알아보고자한다. 분사율은1, 2이고횡방향분사각은22.5°이다. 분사율이1일때평행형상에서는안티키드니와류가잘형성되어막냉각효율이수직형상의경우보다더높다. 반면에분사율이2일때수직형상의막냉각효율은평행형상보다향상되었다. 많은유량의제트가서로반대방향으로분사되기때문에두형상모두막냉각효율이높게나타난다. 하지만안티키드니와류의영향은다른분사율보다상대적으로작다.Abstract: Several studies of film cooling were accomplished with a secondary flow channel parallel to themain flow. In real turbine blades, however, the direction of the secondary flow channel is generally normalto the main flow. Thus, this study performs a numerical analysis to investigate the effects of the direction ofsecondary flow on the effectiveness of double-jet film cooling. The blowing ratio is 1 and 2, and the lateralinjection angle is 22.5°. The parallel channel case creates a well-developed anti-kidney vortex with a blowingratio of 1, and the laterally averaged film cooling effectiveness of the parallel channel is enhanced comparedto the normal channel. The normal channel shows higher performance with a blowing ratio of 2. Both casesshow high film cooling effectiveness. These phenomena can be attributed to a high blowing ratio and flowrate rather than an anti-kidney vortex.