International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 11, November 2018, pp. 1699 1718, Article ID: IJMET_09_11 178 Available online at http://www.ia aeme.com/ijmet/issues.asp?jtype=ijmet&vtype= =9&IType=11 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed ON IMPROVING FILM COOLING EFFECTIVENESS OF COMBUSTOR LINER PLATES OF GAS TURBINES BY USING WEDGE PLATES Jayakumar J S Department of Mechanical Engineering, Amrita Vishwa Vidyapeetham, Amritapuri, India ABSTRACT The present paper introduces a new design concept, which increases the adiabatic cooling effectiveness of simple cylindrical film cooling holes. This design is achieved by placing two wedge plates downstream of a cylindrical coolant hole. A row of nine simple cylindrical holes on a flat plate with pitch / diameter = 3.0, length / diameter = 3.5 and an inclination angle of 35 deg is taken as the reference geometry. Adiabatic film cooling effectiveness of the cylindrical hole with and without downstream wedge plates was numerically estimated using CFD analysis. The effect of three parameters: blowing ratio (0.5, 1.0, and 1.5), wedge height (0.25D, 0.50D, 0.75D, and D) and the distance between the wedges (0.25D, 0.50D, 0.75D, and D) were studied for the newly introduced geometry. The results obtained show that presence of wedge plates increases the adiabatic film cooling effectiveness as compared to the effectiveness of the simple cylindrical coolant hole. It is also observed that even under high blowing ratio, the proposed design provides better film cooling effectiveness. A detailed analysis was also done to find the best geometric dimension for the wedge plates, which will provide optimumm film cooling effectiveness. Keyword: Wedge Plate, Combustor Liner, Gas Turbine, Cooling Effectiveness, Film Cooling, CFD. Cite this Article: Jayakumar J S, On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates, International Journal of Mechanical Engineeringg and Technology, 9(11), 2018, pp. 1699 1718. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=9&i IType=11 http://www.iaeme.com/ijmet/index.asp 1699 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates NOMENCLATURE A Area, m 2 BR Blowing Ratio Specific heat, J/kgK D Diameter of cooling hole, mm DR Density Ratio Kinetic Energy, J Acceleration due to gravity, m/s 2 h Heat transfer coefficient, W/m 2 K k e Effective conductivity, W/mK k Thermal conductivity, W/mK M Mass Flow, kg/s P Pressure, Pa Volumetric heat source, W/m 3 Distributed resistance T Temperature, K Total / stagnation temperature, K v Velocity, m/s Viscous work term, J Greek Symbols η Adiabatic Cooling Effectiveness ρ Density, kg/m 3 Effective viscosity, kg/ms Φ Viscous heat generation term, J τ Viscous loss term Subscripts c Coolant f Film m Mainstream w Wall x, y, Global Cartesian coordinates z 1. INTRODUCTION Thermal efficiency and specific thrust of a gas turbine engine can be increased by operating it with high inlet temperatures of the gases. However, the inlet temperature is usually limited by the temperature withstanding capability of the turbine components, as the metals and alloys with which they are made of, become weak when exposed to high temperatures. Therefore, cooling technologies are implemented to allow high rotor inlet temperature, without affecting the structural integrity of turbine components. Film cooling technology is one of the cooling methods, which is widely used for protection of the combustor liner of gas turbines. In film cooling, a low-temperature air or gas is injected onto the surface of the combustor liner through discrete holes. These jets of low-temperature air or gas forms a protective film on the surface restricting the direct contact of hot mainstream gas with the surface of the combustor liner. http://www.iaeme.com/ijmet/index.asp 1700 editor@iaeme.com
Jayakumar J S In the past 30 years, significant amount of experimental and numerical studies to estimate the film cooling effectiveness of single and multiple row cylindrical holes have been conducted. Major conclusions obtained from all these studies are; (i) the film cooling effectiveness of the cylindrical hole is good at low values of blowing ratios and (ii) effectiveness drops with increase of blowing ratio. This is due to the formation of counterrotating vortices when the coolant jet interacts with the oncoming mainstream gas in cross flow. These vortices often referred to as kidney-shaped vortices that promote both the jet liftoff. A few research works have been conducted on shaped coolant holes and its effect on film cooling performance. Shaped holes have proved to provide high effectiveness among various film cooling configurations (Goldstein et al. [1], Hyams et al. [2], Schmidt et al. [3] and Jung et al. [4]). However, the manufacturing of shaped holes is expensive. Instead of using coolant holes with shaped exits, Nasir et al. [5] have introduced a design concept where tabs are placed at the upstream edge of the holes. The results showed that film cooling effectiveness is increased at high blowing ratio due to the presence of the horizontal tabs. Bunker [6] studied the effect of trenched hole, where the continuous surface slots were fed by the internal discrete film holes, on cooling effectiveness. This geometry was found to provide higher film cooling effectiveness than the simple cylindrical holes. The effects of trenched hole using (i) cylindrical hole and (ii) forward diffusion hole was studied by Baheri et al. [7]. They used both normal injection and compound angle injection. A trenched compound angle injection shaped hole proved to have best heat protection capacity than the other configurations investigated in their paper. Several researchers such as Somawardhana and Bogard [8], Borigozzi et al. [9], Lu et al. [10], Waye and Bogard [11], Harrison and Bogard [12], Zuniga and Kapat [13], Jia et al. [14] have investigated various trench configurations. Na and Shih [15] have introduced a new design concept, in which an upstream ramp with backward-facing step was placed in front of the cooling exit. It was found that the laterally averaged adiabatic effectiveness with a ramp is twice or higher than that without the ramp. Barigozzi et al. [16] proved that the presence of a modified ramp at the upstream of the cylindrical hole improves the thermal protection by 40%. Rigby and Heidmann [17] placed a delta shaped vortex generator at the downstream of cylindrical coolant hole. The results manifested that the delta vortex generator can destroy the kidney-vortex pair by producing an anti-kidney-vortex pair. The resultant anti-vortex pair causes the coolant jet to remain adhered to the wall and spreads out along the wall. A method to improve the effectiveness of film cooling by placing a short crescent shaped block at the downstream of cooling holes was presented by An et al. [18]. The results showed considerable increase in lateral averaged cooling effectiveness when the downstream block is present. Abdala et al. [19] have studied the effect of twenty-one types of different upstream steps on film cooling effectiveness and flow structures. Later Abdala et al. [20] investigated the improvements in film cooling effectiveness by using upstream novel steps. These steps were curved rather than of normal shapes. Results showed that higher laterally film cooling effectiveness is obtained for the curved step with lesser width. In a bid to reduce the lift-off of the coolant stream from the surface, Yash and Jayakumar [21] suggested a method in which grooves are provided downstream of the angled circular holes. It is reported that this configuration can increase the film cooling effectiveness by a minimum of 12%. In the present study a new configuration, which can prevent kidney-vortices and thus increase the film cooling effectiveness, is proposed and its performance is analysed in detail. In this design, two wedge plates are placed at the downstream location of each cylindrical coolant hole to improve the film cooling effectiveness. Fabrication of this design is easier as http://www.iaeme.com/ijmet/index.asp 1701 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates compared to shaped holes and steps. Detailed parametric studies of the design, viz., wedge height and distance between the wedges are carried out for different blowing ratios. Section 2 deals with the methodology adapted for analysis and its validation. Design concepts of the wedge system is given in section 3 and the results and the optimum design are discussed in section 4. 2. METHODOLOGY In a gas turbine, a portion of the air from the compressor goes to the combustor (mainstream flow) and the remaining air is used for cooling the turbine components (coolant flow). The ratio of mass of mainstream gas to that of coolant gas is termed blowing ratio, BR. ρ U c c BR = (1) ρ U m m Ratio of density of the mainstream gas to that of coolant gas is termed Density Ratio (DR). Adiabatic Film Cooling Effectiveness is determined by estimating the parameter, η = ( T T g w ) ( T T g c ) The governing equations used to model the thermo-fluidic analysis is given below. (2) 2.1. Mass Conservation ( ρu) ( ρv) ( ρw) ρ + + + = 0 t x y z (3) 2.2. Momentum Conservation 2.2.1. x-momentum ( ρ ) ( ρ ) ( ρ ) ( ρ ) u uu uv uw P + + + = ρ g + R + x x t x y z x u u u µ µ µ e + + e e x x y y z z (4) 2.2.2. y-momentum ( ρ ) ( ρ ) ( ρ ) ( ρ ) v uv vv vw P + + + = ρ g + R + y y t x y z y v v v µ µ µ e + + e e x x y y z z (5) http://www.iaeme.com/ijmet/index.asp 1702 editor@iaeme.com
Jayakumar J S 2.2.3. z-momentum ( ρ ) ( ρ ) ( ρ ) ( ρ ) w uw vw ww P + + + = ρg + R + z z t x y z z w w w µ µ µ e + + e e x x y y z z (6) 2.3. Energy Conservation ( ρct ) ( ρuct ) ( ρvct ) ( ρwct ) + + + = t x y z w w w v k P µ + µ + µ + W + E + Φ + x x y y z z t (7) The viscous work term is: W = uµ + + + 2 2 2 + + + x y z x x y z 2 2 2 v u u u u v w 2 2 2 v v v u v w vµ + + + 2 2 2 + + + x y z x x y z 2 2 2 w w w u v w wµ + + + 2 2 2 + + x y z x x y z The kinetic energy term is: k k 1 2 k 1 2 k 1 2 E = V V V x c x 2 y c y 2 z c z 2 (9) The viscous dissipation term is: 2 2 2 u v w Φ = 2µ + + + x y z 2 2 2 v u v w w u µ + + + + + x y z y x z (10) 2.4. Turbulence model Based on the validation results, the turbulence model used in in this analysis is the Reynolds- Averaged Navier-Stokes (RANS) approach using the realizable k-epsilon two-equation model. This model has one equation for the turbulence kinetic energy (k) and another one for its dissipation rate (ε). The turbulent kinetic energy equation is, (8) http://www.iaeme.com/ijmet/index.asp 1703 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates ( ) ( ) ( ) ( ) ρk ρuk ρvk ρ wk µ k t x y z x σ x k t + + + = + µ k µ k t t + + µ Φ ρε + t σ σ k k y y z z C βµ 4 t T T T g + g + g x y z σ x y z t The dissipation rate equation is ( ) ( u ) ( v ) ( w ) ρò ρ ò ρ ò ρ ò µ ò t x y z x σ x ò t + + + = + 2 µ ò µ ò ε ε t t + + C µ φ C ρ + 1ε t 2 y σ y z σ z k k ò ò ( 1 ) C C βρk µ 2 T T T g + g + g x y z σ x y z t (11) (12) 2.5. Solution Methodology The continuity, momentum, energy and transport equations for turbulence (3 to 12) for the film-cooling problem were solved using the SIMPLE algorithm. Here we are looking for a solution to an engineering problem, by which better cooling can be provided to the turbine component. The geometries under consideration are complex and it is highly turbulent flow situation with heat transfer. Hence, the CFD package ANSYS Fluent v17.0 was used to carry out this investigation. This is an engineering design application and hence use of the commercial CFD code can be justified. Computational analysis was carried out until the required convergence was attained. The mass, velocity and energy were taken to be converged when the normalized residuals of these parameters were less than 10 5. For the turbulence quantities, when the normalized residuals less than 10 4, convergence is considered to be attained. 2.6. Validation The methodology and the choice of turbulence model used in this computational work is to be validated by solving a similar problem before it can be applied to the problem at hand. This is done by comparing the data obtained in by numerical analysis with the experimentally measured values given by Kohli and Bogard [22]. Figure 1 shows flat plate with simple cylindrical holes used for validation. The diameter (D) of each hole is 0.0111 m. The adjacent holes in a row are at a pitch of 3D, and the length (L) of each coolant hole is 3.5D. The boundary and operating conditions are kept to be same as that of the experimental wok [22]. Air is the working fluid for both main flow hot gas and the coolant. The mainstream hot air is entering the domain with a constant temperature (T m ) of 298 K and coolant air is entering with a temperature (T c ) of 188 K. Hence, the density ratio (DR) is 1.6. The coolant air is entering the coolant holes with an average velocity, U c of 6.25 m/s. A blowing ratio (BR) of 0.5 is obtained by keeping the free stream velocity, U m = 20 m/s. Adiabatic and no-slip boundary condition are applied to the surface of the flat plate and to the other walls. Atmospheric pressure is maintained at the pressure outlet. http://www.iaeme.com/ijmet/index.asp 1704 editor@iaeme.com
Jayakumar J S (a) (b) Figure 1 Dimensions of baseline geometry To compare the results, the centerline adiabatic wall effectiveness (η) and laterally averaged adiabatic effectiveness were calculated for the geometry. Centerline line adiabatic effectiveness is obtained along the central line of the central hole at x/d = 0.5, 1, 1.5, 2, 3, 5, 6, 8, 10, 15, 22, 30 and 50. For laterally averaged adiabatic effectiveness, adiabatic wall effectiveness was calculated at ten equally spaced points along the span wise (-1.5 y/d 1.5) at locations x/d = 3, 6, 10 and 15. Laterally averaged adiabatic effectiveness was obtained by integrating the measured adiabatic effectiveness along the span wise direction and dividing by distance between the holes. The integration was done by using Simpson s 1/3 rd rule. The results obtained from the above-selected grid for the baseline geometry is compared against the experimental values [22] for the case of simple cylindrical holes with a diameter of 11.1 mm, injection angle of 35 deg, L/D of 3.5, P/D of 3 and blowing ratio of 0.5. Figure 2 shows the comparison between the experimental values and the present computational work. The computed results of centerline adiabatic effectiveness agrees with the experimental data. http://www.iaeme.com/ijmet/index.asp 1705 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates 3. PROPOSED DESIGN The new design is achieved by placing two wedge plates, downstream of a cylindrical coolant hole. Figure 3 shows the placement and geometry of the wedge plates downstream of each simple cylindrical hole. 1 0.9 0.8 0.7 0.6 Kohli and Bogard [21] present study η 0.5 0.4 0.3 0.2 0.1 0 0 10 20 30 x/d 40 50 60 Figure 2 Comparison of centerline adiabatic effectiveness. The diameter (D) of each hole is 11.1 mm. The adjacent holes in a row are pitched to a distance of 3D from each other, and the length of each coolant hole is 3.5D. The wedge length (3D) and wedge angle (2 degrees) are the dimensions that are kept constant in the present study. Numerical analysis is performed for four wedge heights: 0.25D, 0.50D, 0.75D and D. Analyses are also conducted by varying the distance between the wedges as 0.25D, 0.50D, 0.75D, and D. (a) http://www.iaeme.com/ijmet/index.asp 1706 editor@iaeme.com
Jayakumar J S (b) Figure 3 Wedge plates placed downstream to the cylindrical hole. The solution methodology (which includes boundary condition and solver settings) followed for the analysis of the proposed geometry is same as the methodology applied for the validation case. Depending on the wedge height and the distance between the wedge plates, the computational mesh is varied from 3.1 million cells to 4.5 million cells. Three different blowing ratios viz., 0.5, 1.0, 1.5 are obtained by varying the free stream velocity (U m ) of the mainstream hot air to 20 m/s, 10 m/s, 6.67 m/s respectively by keeping constant coolant velocity (U c ) of 6.25 m/s. Figure 4 gives the results of grid independency study. 4. RESULTS AND DISCUSSION This study was conducted to observe the enhancement of cooling effectiveness of simple cylindrical holes by introducing wedge plates downstream of the holes. The design without the wedge plate is termed as baseline geometry. Figure 5 shows the adiabatic effectiveness contours on the surface of flat plate, with and without the wedge plates. Figure 6 shows the effectiveness contours on plane y/d = 0, for cylindrical coolant hole, with and without wedge plates. It can be observed from figure 5 and 6 that due to the presence of the wedge plates, the film spreads out more and remains attached to the plate surface as compared to the case without wedge plates. The jet lift-off in case of baseline geometry is due to the formation of counter-rotating vortex pair [23]. However, the presence of downstream wedge plates suppresses the formation of counter-rotating vortex pair, as it can be observed from figure 7. http://www.iaeme.com/ijmet/index.asp 1707 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates 1.2 1 0.8 First grid, 3.112 million cells second grid, 4.408 million cells η 0.6 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 4 Effectiveness for three different grids (a) (b) Figure 5 Adiabatic effectiveness on the flat plate (A=D, H=D, BR=1.5); (a) without wedge; and (b) with wedge. http://www.iaeme.com/ijmet/index.asp 1708 editor@iaeme.com
Jayakumar J S (a) (b) Figure 6 Adiabatic effectiveness on the flat plate on plane y=0 (A=D, H=D, BR=1.5) (a) without wedge; and (b) with wedge. (a) (b) Figure 7 Adiabatic effectiveness contours and velocity vectors on plane x/d=1.5 (a) without wedge plates (b) with wedge plate. Numerical analysis was done by varying (i) the distance between the wedge plates (A) and (ii) the wedge height (H) (See Fig. 3). These analyses were carried out for a blowing ratio (BR) of 1.5, as the effect of kidney vortices would be maximum at the highest possible BR. The velocity vectors and effectiveness contours were captured for these cases to observe the effect of wedge geometry on the counter-rotating vortex pair. Initially the wedge height is kept constant and the effect of wedge spacing on cooling effectiveness is studied. Subsequently the effect of wedge height is analysed. http://www.iaeme.com/ijmet/index.asp 1709 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates Figure 8 shows the effect of distance between the wedge plates, for a wedge height of D and the blowing ratio of 1.5. Figure 8(a) shows the effectiveness contours and tangential velocity vectors above the test plate for the baseline geometry on plane x/d = 1.5. Similarly, figure 8(b), 8(c), 8(d) and 8(e) shows the effectiveness contours and tangential velocity vectors for different wedge plate distances, A = D, 0.75D, 0.50D and 0.25D apart on plane x/d = 1.5 respectively. (a) (b) (c) (d) (e) http://www.iaeme.com/ijmet/index.asp 1710 editor@iaeme.com
Jayakumar J S Figure 8 Adiabatic effectiveness and velocity vectors on plane x/d=1.5 (H = D, BR = 1.5): (a) without wedge plates; (b) (e) with wedge plate,; (b) A=D; (c) A=0.75D; (d) A=0.50D and (e) A=0.25D. It can be observed from the figure 8 that due to the presence of wedge plates, the size of the kidney-vortices formed due to the interaction between mainstream hot gas and injected coolant decreases when compared to the size of the kidney-vortices formed for the case of without wedge plates. The decrease in the size of the kidney-vortices in the case of A=0.25 D and A=0.50 D is less as compared to the baseline case. However, for the cases A=0.75 D and A=D the size of the kidney-vortices are largely reduced. This lesser strength of kidneyvortices for A=D and A=0.75D, causes the coolant jet to remains attached to the plate surface for a large distance downstream the coolant hole thus increasing the adiabatic film cooling effectiveness. This can be observed in figure 9 that the centreline adiabatic effectiveness is higher for A = D and 0.75D ascompared to other cases (baseline, A = 0.50D and 0.25D). 1.2 baseline, BR=1.5 η 1 0.8 0.6 A=D, H=D, BR=1.5 A=0.75D, H=D, BR=1.5 A=0.50D, H=D, BR=1.5 A=0.25D, H=D, BR=1.5 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 9 Comparison of centreline adiabatic effectiveness of baseline geometry with the proposed design (H=D, BR=1.5) at different distances between the plates (A=D, 0.75D, 0.50D, and 0.25D). Figure 10 shows the effect of wedge heights (H) on the film cooling effectiveness at a blowing ratio of 1.5. In this case, the wedge plates are placed at a constant distance of D apart. Figure 10(a) gives the effectiveness contours and tangential velocity vectors above the test plate for the baseline geometry on plane x/d = 1.5. Similarly, figure 10(b), 10(c), 10(d) and 10(e) gives the effectiveness contours and tangential velocity vectors for different wedge plate heights; H = D, 0.75D, 0.50D and 0.25D apart on plane x/d = 1.5 respectively. It can be observed that, as the wedge height is decreased from D to 0.25D, the strength of the kidneyvortices and the entrainment of hot air increases. This increases the chance of jet lift-off due http://www.iaeme.com/ijmet/index.asp 1711 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates to the increased strength of the kidney-vortices. Thus, the film cooling effectiveness decrease as the wedge height is decreased. Figure 11 shows the centreline adiabatic effectiveness for different wedge heights. Thus for the further analysis, the height of the wedge plates was taken as D, because of its best results (figure 10). The effects of different blowing ratios (0.5, 1.0, 1.5) and different wedge distances, A = D and 0.75D (optimized from figure 9) are then studied in detail. The effect of distance between the wedge plates, A=D and A=0.75D apart (wedge height, H=D and blowing ratio, BR=0.5) on the centreline adiabatic film cooling effectiveness is depicted in Figure 12. The presence of wedge plates increases the film cooling effectiveness. It is observed that the centreline adiabatic film cooling effectiveness is maximum for the case where A=0.75D when compared to the other two cases (A=D, and baseline). From the figure, it is observed that for the blowing ratio of 0.5, the proposed design provides optimum results when the two wedge plates are placed 0.75D apart. (a) (b) (c) (d) http://www.iaeme.com/ijmet/index.asp 1712 editor@iaeme.com
Jayakumar J S (e) Figure 10 Adiabatic effectiveness and velocity vectors on plane x/d=1.5 (A=D, BR=1.5): (a) without wedge plates; (b) with wedge plate of height D; (c) with wedge plate of height 0.75D; (d) with wedge plate of height 0.50D; and (e) with wedge plate of height 0.25D. 1.2 1 0.8 baseline, BR=1.5 H=D, A=D, BR=1.5 H=0.75D, A=D, BR=1.5 H=0.50D, A=D, BR=1.5 H=0.25D, A=D, BR=1.5 η 0.6 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 11 Comparison of centerline adiabatic effectiveness of baseline geometry with the proposed design (A=D, BR=1.5) at different distances wedge heights (H=D, 0.75D, 0.50D, and 0.25D). The effect of distance between the wedge plates for A=D and A=0.75D (wedge height, H=D and blowing ratio, BR=1.0) on the centreline adiabatic film cooling effectiveness is shown in figure 13. It is observed that the presence of wedge plates improve the film cooling effectiveness by an average of 40% for both the cases (A=D, 0.75D apart) as compared to the baseline case. Near the coolant hole (0 x/d 8) the adiabatic effectiveness for A=0.75D is more effective than for A=D. http://www.iaeme.com/ijmet/index.asp 1713 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates 1.2 1 0.8 baseline, BR=0.5 A=D, H=D, BR=0.5 A=0.75D, H=D, BR=0.5 η 0.6 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 12 Comparison of adiabatic effectiveness of baseline geometry with the proposed design (H=D, BR=0.5), when wedges are placed at D and 0.75D distance apart along centreline 1.2 1 0.8 baseline, BR=1.0 A=D, H=D, BR=1.0 A=0.75D, H=D, BR=1.0 η 0.6 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 13 Comparison of adiabatic effectiveness of baseline geometry with the proposed design (H=D, BR=1.0), when wedges are placed at D and 0.75D distance apart along centreline. The effect of distance between the wedge plates, A=D, and A=0.75D apart (wedge height, H=D and blowing ratio, BR=1.5) on centreline film cooling effectiveness is presented in figure 14. http://www.iaeme.com/ijmet/index.asp 1714 editor@iaeme.com
Jayakumar J S 1.2 1 baseline, BR=1.5 A=D, H=D, BR=1.5 A=0.75D, H=D, BR=1.5 0.8 η 0.6 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 14 Comparison of adiabatic effectiveness of baseline geometry with the proposed design (H=D, BR=1.5), when wedges are placed at D and 0.75D distance apart: (a) along centreline; and (b) along spanwise. It is seen from the figure 14 that the attachment of the film coolant jet to the plate surface is more when the distance between the wedge plates is A=0.75D. In the case of A=D, we observed a jet lift off near the coolant hole. Thus, from the analysis of figures 12 to 14, it can be found that the wedge plates provides an improvement in film cooling effectiveness when the two wedges are placed at a distance of 0.75D apart. Figure 15 graphically compares the centreline adiabatic film cooling effectiveness of proposed design (A=0.75D, H=D) with the baseline geometry for three different blowing ratios (BR=0.5, 1.0, 1.5). From this figure, it can be seen that, under all blowing ratios, the proposed geometry (simple cylindrical holes with wedge plates), provides better film cooling effectiveness as compared to the film cooling effectiveness provided by baseline geometry (simple cylindrical holes without wedge plates). Thus, the presence of downstream wedge plates yields improvement in film cooling effectiveness when operated at high blowing ratios. http://www.iaeme.com/ijmet/index.asp 1715 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates 1.2 1 baseline, BR=0.5 baseline, BR=1.0 baseline, BR=1.5 A=0.75D, H=D, BR=0.5 0.8 A=0.75D, H=D, BR=1.0 η A=0.75D, H=D, BR=1.5 0.6 0.4 0.2 0 0 10 20 30 40 50 60 x/d Figure 15 Comparison of the centerline adiabatic film cooling effectiveness of proposed design (A=0.75D, H=D) with the baseline geometry for three different blowing ratios (BR=0.5, 1.0, and 1.5). 5. CONCLUSION Analysis for estimation of adiabatic cooling effectiveness of film cooling with and without the presence of wedge plate have been carried out. ANSYS fluent 17.0 solver was used to generate the numerical results. The methodology and models used and benchmarked. It has been observed that the counter rotating kidney vortices causes lift of the cooling film and leads to deterioration of cooling effectiveness. Based on the results, a design to improve the adiabatic effectiveness of film cooling by placing two wedge plates downstream of each film cooling holes is given. Computational work was also done to analyze the effect of different wedge heights (H=D, 0.75D, 0.50D and 0.25D), different distances between the two wedge plates (A= D, 0.75D, 0.50D and 0.25D apart) under three different blowing ratios (BR=0.5, 1.0, 1.5). The following conclusions were drawn from the results obtained in the numerical analysis. Under all blowing ratios (0.5, 1.0, and 1.5), presence of wedge plates improves the adiabatic film cooling effectiveness of simple cylindrical holes when compared to that of simple cylindrical holes without wedge plates. Wedge plates of height H=D, provide optimum improvement in film cooling effectiveness when placed A=0.75D apart. http://www.iaeme.com/ijmet/index.asp 1716 editor@iaeme.com
Jayakumar J S The proposed geometry yields better percentage improvement in film cooling effectiveness compared to baseline geometry when operated under higher blowing ratios. ACKNOWLEDGEMENT The author sincerely acknowledge contribution of Mr. Praveen Kumar Reyyi in preparing this article. REFERENCES [1] R. J. Goldstein, E. R. G. Eckert, and F. Burggraf. "Effects of hole geometry and density on three-dimensional film cooling." International Journal of Heat and Mass Transfer 17(5), (1974), 595-607. [2] G. Hyams Daniel, and James H. Leylek. "A detailed analysis of film cooling physics: Part III streamwise injection with shaped holes." ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, (1997). [3] L. Schmidt Donald, BasavSen, and David G. Bogard. "Film cooling with compound angle holes: adiabatic effectiveness." Journal of Turbomachinery 118(4) (1996), 807-813. [4] Jung In Sung, and JoonSik Lee. "Effects of orientation angles on film cooling over a flat plate: boundary layer temperature distributions and adiabatic film cooling effectiveness." Journal of Turbomachinery 122(1) (2000), 153-160. [5] H. Nasir, S. Acharya, and S. Ekkad. "Improved Film Cooling From Cylindrical Angled Holes With Triangular Tabs: Effect of Tab Orientations," Int. J. Heat Fluid Flow, 24, (2003), 657-668. [6] R. S. Bunker, Film Cooling Effectiveness Due to Discrete Holes Within a Transverse Surface Slot, ASME Paper No. GT2002-30178, (2002) [7] S. Baheri, S. P. A. Tabrizi, and B. A. Jubran. "Film Cooling Effectiveness From Trenched Shaped and Compound Holes," Heat Mass Transfer, 44, (2008), 989-998. [8] R. P. Somawardhana, and D. G. Bogard. "Effects of Obstructions and Surface Roughness on Film Cooling Effectiveness With and Without a Transverse Trench," ASME J. Turbomachinery., 133, (2009) p. 011010. [9] G. Barigozzi, G. Franchini, A. Perdichizzi, and S. Ravelli,, "Effects of Trenched Holes on Film Cooling of a Contoured Endwall Nozzle Vane," ASME J. Turbomach., 134, (2012) p. 041009. [10] Y. Lu, H. Nasir, S.V. Ekkad, Film cooling from a row of holes embedded in transverse slots, (2005), ASME Paper GTI2005-68598. [11] S. Waye, D. Bogard, High resolution of film cooling effectiveness measurements of axial holes embedded in a transverse trench with various trench configurations, ASME J. Turbomach. 129 (2007) 294 302. [12] K.L. Harrison, D.G. Bogard, CFD predictions of film cooling adiabatic effectiveness for cylindrical holes embedded in narrow and wide transverse trenches, (2007), ASME Paper GT2007-28005. [13] H.A. Zuniga, J.S. Kapat, Effect of increasing pitch-to-diameter ratio on the film cooling effectiveness of shaped and cylindrical holes embedded in trenches, (2009), ASME Paper GT2009-60080. [14] L. Jia, R. Jing, J. Hongde, Film cooling performance of the embedded holes in trenches with compound angles, ASME Paper GT2010-22337. [15] S. Na, and T. I. Shih, Increasing Adiabatic Film-Cooling Effectiveness by Using an Upstream Ramp, ASME J. Heat Transfer, 129, (2007), 464-471. http://www.iaeme.com/ijmet/index.asp 1717 editor@iaeme.com
On Improving Film Cooling Effectiveness of Combustor Liner Plates of Gas Turbines by Using Wedge Plates [16] G. Barigozzi, G. Franchini, A. Perdichizzi, The effect of an upstream ramp on cylindrical and fan-shaped hole film cooling Part II: adiabatic effectiveness results, (2007), ASMEpaper GT2007-27079. [17] D. L. Rigby, and J. D. Heidmann, Improved Film Cooling Effectiveness by Placing a Vortex Generator Downstream of Each Hole, (2008), ASME Paper No. GT2008-5136I. [18] B. An, J. Liu, C. Zhang, & S. Zhou. Film cooling of cylindrical hole with a downstream short crescent-shaped block, Journal of Heat Transfer, 135(3), 031702, 2013. [19] A.M.M. Abdala, F.N.M. Elwekeel, D. Huang. Film cooling effectiveness and flow structures for novel upstream steps, Appl. Therm. Eng. 105, (2015), 1 14. [20] AbdalaAntar MM, and Fifi NM Elwekeel. "An influence of novel upstream steps on film cooling performance." International Journal of Heat and Mass Transfer 93 (2016), 86-96. [21] Yash Krishna Menon and Jayakumar J. S., Numerical Simulation to Investigate Effect of Downstream Grooves on Film Cooling Effectiveness of Gas Turbine Blades, International Journal of Mechanical Engineering and Technology, 8(1), (2017), 304 316. [22] A. Kohli, and D. G. Bogard. Adiabatic effectiveness, thermal fields, and velocity fields for film cooling with large angle injection. Journal of Turbomachinery 119(2). (1997), 352-358. [23] B. A. Haven, and M. Kurosaka. "Kidney and anti-kidney vortices in cross flow jets." Journal of Fluid Mechanics 352, (1997), 27-64. http://www.iaeme.com/ijmet/index.asp 1718 editor@iaeme.com