Eui Yeop Jung

Total Cooling Effectiveness on a Staggered Full-Coverage Film Cooling Plate With Impinging Jet

In the present study, total cooling performance was experimentally investigated on a full-coverage film cooling plate with an impingement jet cooling array. The detailed temperature distributions on the film cooled surface were measured using an infra-red thermographic technique. The test plate was made of polycarbonate (k = 0.2 W/m·K) and an array jet impinged underneath the test plates. The measured cooling effectiveness is a combined result of film cooling on the surface and convective heat transfer by a jet impingement array underneath the test plate. The diameter (d) of both film cooling and impingement jet cooling holes was 5 mm. Both the streamwise and spanwise hole spacing-to-hole diameter ratios (p/d) were 3 on the film cooled plate and impingement nozzle plate. The inclination angles of the film cooling holes and impingement jet holes were 35° and 90°, respectively. The holes on each plate were arranged in a staggered pattern. The jet Reynolds number based on the hole diameter varied from 3,000 to 7,000 and the equivalent blowing rate (M) changed from 0.3 to 0.7. The combined cooling effectiveness was measured by changing the gap distance between the jet plate and the film cooling plate from 1 to 5 times the hole diameter. The staggered film cooling hole arrangement showed a higher film cooling effectiveness than the inline film cooling hole arrangement. As the blowing rate increased, the cooling effectiveness decreased on the front part of film cooling plate for a fixed height to diameter ratio (H/d). The effect of H/d on the total cooling effectiveness was not significant for the fixed blowing rate (M) in the tested range.Copyright

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.

Effect of impingement jet on the full-coverage film cooling system with double layered wall

ABSTRACT The present study was conducted to evaluate the total cooling effectiveness in combined full-coverage film cooling and impingement jet using an infrared thermographic technique. The effect of film cooling hole angle, blowing ratio, and height to diameter ratio between the film cooling and impingement jet plates was discussed. The total cooling effectiveness increased as impingement jet cooling was added. The angled film cooling holes had approximately 4.6% higher total cooling effectiveness than the normal film cooling holes. The total cooling effectiveness was almost constant regardless of height to diameter ratio, but enhanced as the blowing ratio was increased.

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

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

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

Enhancement of Film Cooling Effectiveness Using Backward Injection Holes

Film cooling is a cooling method used to protect the hot components of a gas turbine from high temperature conditions. For this purpose, high and uniform film cooling effectiveness is required to protect the vanes/blades from excessive thermal stress. Backward injection is proposed as one of the methods for the improvement of film cooling effectiveness. In this study, experiments were performed to investigate the effect of backward injection on film cooling effectiveness, using pressure sensitive paint (PSP) method. Four experimental configurations were composed of forward and backward injection cylindrical holes. The cylindrical holes were aligned in two staggered rows with pitch (p) of 6d and row spacing (s) of 3d. The injection angles (α) of the cylindrical holes were 35° and 145° for forward and backward injection, respectively. The blowing ratios (M) ranged from 0.5 to 2.0 and the density ratio (DR) was about 1. The results indicate that backward injection enhanced not only film cooling effectiveness but also the lateral cooling uniformity. At a high blowing ratio, all configurations demonstrated higher film cooling effectiveness with backward injection than with only forward injection; thus, the dispersion of the backward injection jets enhanced the lateral coverage over wide areas. Configuration, in particular, arranged with forward injection in the first row and backward injection in the second row, obtained the highest film cooling effectiveness among the four cases studied, due to the dispersion of the backward injection jets and the coolant supply from the forward injection jets at a high blowing ratio.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

Heat Transfer Characteristics of an Angled Array Impinging Jet on a Concave Duct

This study investigated the heat transfer characteristics of an array jet cooling system on a concave surface. Two types of injection holes were used: one for impinging jets normal to the impingement surface, and the other for angled impinging jets. For the normal jets, the jet Reynolds number (Re) based on the hole diameter varied from 3,000 to 10,000, and the height-to-diameter ratio (H/d) was fixed at 1.0. There were 15 injection holes positioned in a staggered 3×5 array. For the angled jets, Re was set to 5,000 and H/d was also fixed at 1.0. Naphthalene sublimation method was used to determine the heat transfer coefficients on the targeted plates. For normal impinging jet cooling, separate peaks were observed at the stagnation regions due to the curvature effect. Since a crossflow was generated by air spent from the jet arrays, the crossflow effect increased as it moved downstream. Due to the interaction between the crossflow and impinging jets, the peak values at the stagnation points increased downstream. The heat transfer coefficient on the targeted plate increased with Re. The average Sh of the angled jets was higher than that of the normal jets, as the obliquely impinging jet increased the mass flow rate and mass interaction between the jet impingement points.Copyright

Effect of Array Jet on Cooling Effectiveness on Full-Coverage Film Cooled Surface

In this study, the cooling effectiveness (Φ) was measured on full-coverage film cooled surface with and without array jet impingement cooing using an infra-red thermographic technique. Measurements were conducted with two test plates of different thermal conductivities. One was made of stainless steel (k = 16.3 W/m·K) and the other was made of polycarbonate (k = 0.2 W/m · K). The measured cooling effectiveness comprises the adiabatic film cooling effectiveness on the film cooled surfaces, the heat conduction through the test plates and convective heat transfer of array jet impingement underneath the test plates. The inclination angles of film cooling holes and impingement jet holes were 35° and 90°, respectively. The diameters of both film cooling and impingement jet cooling holes were 5 mm. The streamwise and spanwise hole spacing-to-hole diameter ratios (p/d) are 3 for both the effusion plate (film cooled plate) and the injection plate (impingement nozzle plate. The holes on each plate were arranged in an inline pattern, while the film cooling holes and jet holes were positioned in a staggered manner. The jet Reynolds number based on the hole diameter was 3,000 and the equivalent blowing ratio (M) was 0.3. The gap distance between the jet plate and the film cooling plate was varied from 1 to 5 times of the hole diameter. In addition, the cooling effectiveness without impingement was tested, too. The stainless steel plate shows relatively higher and uniform cooling effectiveness than the polycarbonate plate. The effect of H/d was not significant for both test plates. However, the cooling effectiveness without the impingement jets decreases significantly for the stainless steel plate, while it changed a little for the cooling effectiveness of the polycarbonate plate.Copyright