Effect of bulk flow pulsations on film cooling with compound angle holes

Experiments are conducted to investigate the effects of bulk flow pulsations on film cooling with compound angle holes. A row of five film cooling holes is considered with orientation angles of 0°, 30°, 60°, and 90° at a fixed inclination angle of 35°. Static pressure pulsations are produced by an array of six rotating shutter blades, which extend across the span of the exit of the wind tunnel test section. The pulsation frequency is fixed at 36 Hz, but changes in the time-averaged blowing ratios of 0.5, 1.0 and 2.0 produce three different coolant Strouhal numbers, 3.6, 1.8 and 0.9, respectively. Detailed film cooled boundary layer temperature distributions are measured by a cold wire and the adiabatic film cooling effectiveness by thermochromic liquid crystal (TLC). The boundary layer temperature surveys show that pulsations induce large disruptions to the boundary layer temperature distribution and the film coverage. As the orientation angle increases, the injectant concentration spreads further into the spanwise direction because of pulsations than the steady case. With pulsations the adiabatic film cooling effectiveness value decreases regardless of the orientation angle. The amount of reduction, however, depends on the orientation angle in such a way that the larger the orientation angle is, the smaller the reduction is.     

不同吹风比下双出口孔射流气膜冷却数值模拟计算

为了获得吹风比对新型气膜冷却孔冷却效率的影响规律,利用Fluent软件求解Navier-Stokes方程,对吹风比分别为0.5、1.0、1.5和2.0时单入口-双出口孔射流冷却效率进行了数值模拟计算,得到了不同吹风比下的流场和冷却效率.结果表明：吹风比对冷却效率有很大影响;随着吹风比的提高,不同次孔方位角下的冷却效率变化规律也不相同;当次孔方位角γ=30°时,吹风比为1.0时的冷却效率最高;当γ=45°时,冷却效率随着吹风比提高而提高;当γ=60°时,冷却效率随着吹风比提高而降低;在研究高吹风比对气膜冷却效率的影响时,γ=45°最佳.     

Film cooling performance of a row of dual-fanned holes at various injection angles

Film cooling performance about a row of dual-fanned holes with injection angles of 30°, 60 ° and 90° were experimentally investigated at blowing ratios of 1.0 and 2.0. Dual-fanned hole is a novel shaped hole which has both inlet expansion and outlet expansion. A transient thermochromic liquid crystal technique was used to reveal the local values of film cooling effectiveness and heat transfer coefficient. The results show that injection angles have strong influence on the two dimensional distributions of film cooling effectiveness and heat transfer coefficient. For the small injection angle of 30 degree and small blowing ratio of 1.0, there is only a narrow spanwise region covered with film. The increase of injection angle and blowing ratio both leads to the enhanced spanwise film diffusion, but reduced local cooling ability far away from the hole. Injection angles have comprehensive influence on the averaged film cooling effectiveness for various x/d locations. As injection angles are 30 and 60 degree, two bands of high heat transfer coefficients are found in mixing region of the gas and coolant. As injection angle increases to 90 degree, the mixing leads to the enhanced heat transfer region near the film hole. The averaged heat transfer coefficient increases with the increase of injection angle.     

A Numerical Evaluation of the Performance of Film Cooling from a Circular Exit Shaped Hole with Sister Holes Influence

The film cooling effectiveness and the jet exit conditions and the associated vortex structure downstream of the injection hole for both a circular exit shaped hole and an elliptical exit shaped holes were numerically investigated for the blowing ratios of 0.25, 0.5, 1, and 1.5. Four turbulence models, including the standard, RNG, realizable k ? ?, and Reynolds-stress model, in combination with three near-wall approaches, were used for the present simulations. It was found that the predicted results using the realizable k ? ? model combined with the standard wall function were in better agreement with the available experimental data from the literature. Further, the results indicate that the circular exit shaped hole improved the centerline and laterally averaged adiabatic effectiveness, particularly at high blowing ratios. Finally, adding the sister holes provided a notable decrease in the strength of the counterrotating vortex pairs, where the highest effectiveness was achieved for the circular exit shaped hole case with sister holes.     

Film cooling characteristics of a single round hole at various streamwise angles in a crossflow: Part I effectiveness

Film cooling effectiveness were studied experimentally on a cylindrical hole with a streamwise angle of 30°, 60° and 90°, in a flat plate test facility with a zero pressure gradient. The short but engine representative hole length (L/D=4) is constant for all three geometries. The blowing ratio ranges from 0.33 to 2, and the freestream Reynolds number based on the freestream velocity and hole diameter (Re_D) was 8563. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The current results are compared with the experimental results obtained by other researchers, and the effects of variations in injection angle are described.There is not a single study on film cooling performance of a single round hole at the three streamwise angles for a wide range of blowing ratios with a short hole length. Therefore, the objective of the present study is to provide a consistent set of measurements in terms of effectiveness and heat transfer coefficients [Int. J. Heat Mass Transfer, 2002] obtained systematically on a flat plate, and to deliver a better understanding of film cooling performance, with explanations deduced from the existing knowledge of a single jet in crossflow, before more engine representative conditions are introduced. The present results also serve as a database for future numerical modelling.     

Effects of film cooling hole shape on heat transfer

The effects of hole shapes, secondary injection Reynolds numbers, and blowing ratios on the heat transfer downstream of film cooling holes have been investigated by using a large‐scale low‐speed loop wind tunnel. The test model consists of five film cooling holes. Experiments on dustpan‐shaped holes, fan‐shaped holes, and round holes have been conducted with injection Reynolds number ranging from 10,000 to 25,000 and blowing ratio ranging from 0.3 to 2.0. Measurements are taken under 26 conditions. Results show that the critical blowing ratio is 1.3 for the dustpan‐ and fan‐shaped holes, 0.7 for the round holes. The turbulence generated by air injection through round holes is stronger than those through dustpan‐ and fan‐shaped holes. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(2): 73–80, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20005     

Investigation of film cooling and superposition method for double row dustpan‐shaped holes

Film cooling effectiveness for injection from single row and double row dustpan‐shaped holes was studied experimentally. The difference in cooling performance between single row and double row holes are described. The results show that the optimal blowing ratio of injection from double row holes is higher than that of injection from a single row hole. In the case of higher blowing ratios, the traditional superposition calculation method underpredicts the film cooling effectiveness of the double row injection based on that of the single row hole injection. The modified superposition calculation method is given in this paper. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(4): 208–217, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20204     

Influence on film cooling effectiveness of novel holes based on cylindrical configurations

In this study, four novel film cooling hole designs, all based on cylindrical holes, are numerically evaluated, and compared with those of a simple cylindrical hole and a laterally-diffused shaped hole. Film cooling effectiveness and surrounding thermal and flow fields are documented for operation with various blowing ratios. It is shown that the two-stage cylindrical hole can improve film cooling effectiveness at higher blowing ratios. The primary hole with two secondary holes can enhance film cooling performance by creating anti-kidney vortex pairs that will weaken jet liftoff caused by the kidney vortex pair that is created by the primary hole. The tri-circular shaped hole provides better film cooling effectiveness values only near the hole, but worse at downstream positions. The two-stage structure for the tri-circular shaped hole provides better film coverage because it changes the flow structure inside the delivery channel and decreases jet penetration into the passage flow.     

Improving film cooling performance by using one -inlet and double-outlet hole

The film cooling performance of a trunk-branch hole is investigated by numerical simulation in this paper. The geometry of the hole is a novel cooling concept, which controls the vortices-pair existing at the mink hole outlet using the injection of the branch hole. The trunk-branch holes require easily machinable round hole as compared to the shaped holes. The flow cases were considered at the blowing ratios of 0.5, 0.75, 1.0, 1.5 and 2.0. At the low blowing ratio of 0.5, the vortices-pair at the outlet of the trunk hole is reduced and the laterally coverage of the film is improved. At the high blowing ratio of 2.0, the vortices-pair is killed by the vortex which is produced by the injection of the branch hole. The flow rate of the two outlets becomes more significantly different when the blowing ratio increases from 0.75 to 2.0. The discharge coefficients increase 0.15 and the laterally averaged film effectiveness improve 0.2 as compared to the cylindrical holes. The optimal blowing ratios occur at M=1.0 or M= 1.5 according to the various locations downstream of the holes.     

Numerical Assessment of the Film Cooling Through Novel Sister-Shaped Single-Hole Schemes

In the present paper, a numerical investigation is conducted on film cooling performance from novel sister-shaped single-hole schemes. Based on the sister hole film cooling technique, shaped holes are formed by merging discrete sister holes to a primary hole. Simulations are performed at four blowing ratios of 0.25, 0.5, 1, and 1.5. The novel-shaped holes resulted in a significant reduction in the jet liftoff effect in comparison with a cylindrical and a forward-diffused shaped hole. Moreover, film cooling effectiveness is notably increased at the high blowing ratios of 1 and 1.5.     

Investigation of the Influence of Inclination Angle and Diffusion Angle on the Film Cooling Performance of Chevron Shaped Hole

The film cooling performance of chevron holes with different inclination angles and exit lateral diffusion angles has been studied experimentally and numerically. The inclination angles include 35° and 55°. The exit lateral diffusion angles include 20° and 25°. The film cooling effectiveness, heat transfer coefficient and discharge coefficient were measured on a flat plate model by transient liquid crystal measurement technique under four blowing ratios. The results show that the large inclination angle reduces the film cooling effectiveness. The influence of diffusion angle has two aspects: the large diffusion angle leads to mainstream ingestion and decreases film cooling effectiveness at M=1.0 and 1.5; however, the large diffusion angle increases the film cooling effectiveness at high blowing ratio of 2.0, because the larger hole exit area decreases the normal momentum component of the film jet. The large inclination angle decreases the heat transfer coefficient in the right downstream region at M=0.5 and 1.0. The large diffusion angle enhances the heat transfer in the right downstream of the holes in M=0.5～1.5 conditions. The chevron hole with large inclination angle generally has the highest discharge coefficient.     

Influence of shaped injection holes on turbine blade leading edge film cooling

To improve the film cooling performance by shaped injection holes for the turbine blade leading edge region, we have investigated the flow characteristics of the turbine blade leading edge film cooling using five different cylindrical body models with various injection holes, which are a baseline cylindrical hole, two laidback (spanwise-diffused) holes, and two tear-drop shaped (spanwise- and streamwise-diffused) holes, respectively. Mainstream Reynolds number based on the cylinder diameter was 7.1 × 10⁴ and the mainstream turbulence intensities were about 0.2%. The effect of injectant flow rates was studied for various blowing ratios of 0.7, 1.0, 1.3 and 1.7, respectively. The density ratio in the present study is nominally equal to one. Detailed temperature distributions of the cylindrical body surfaces are visualized by means of an infrared thermography (IRT). Results show that the conventional cylindrical holes have poor film cooling performance compared to the shaped holes. Particularly, it can be concluded that the laidback hole (Shape D) provides better film cooling performance than the other holes and the broader region of high effectiveness is formed with fairly uniform distribution.     

Numerical approach to hole shape effect on film cooling effectiveness over flat plate including internal impingement cooling chamber

Numerical approach have been conducted on a flat, three-dimensional discrete-hole film cooling geometries that included the mainflow, injection tubes, impingement chamber, and supply plenum regions. The effects of blowing ratio and hole’s shape on the distributions of flow field and adiabatic film cooling effectiveness over a flat plate collocated with two rows of injection holes in staggered-hole arrangement were studied. The blowing ratio was varied from 0.3 to 1.5, while the density ratio of the coolant to mainstream is kept at 1.14. The geometrical shapes of the vent of the cooling holes are cylindrical round, simple angle (CYSA), forward-diffused, simple angle (FDSA) and laterally diffused, simple angle (LDSA). Diameter of different shape of cooling holes in entrance surface are 5.0 mm and the injection angle with the main stream in streamwise and spanwise are 35° and 0° respectively. Ratio of the length of the cooling holes and the diameter in the entrance surface is 3.5. The distance between the holes in the same row as well as to the next row is three times the diameter of hole in the entrance surface.The governing equation is the fully elliptic, three-dimensional Reynolds-averaged Navier–Stokes equations. The mesh used in the finite-volume numerical computation is the multi-block and body-fitted grid system. The simulated streamwise distribution of spanwise-averaged film cooling effectiveness exhibited that low Reynolds number k–ε model can give close fit to the experimental data of the previous investigators. Present study reveals that (1) the geometrical shape of the cooling holes has great effect on the adiabatic film cooling efficiency especially in the area near to the cooling holes. (2) The thermal-flow field over the surface of the film-cooled tested plate dominated by strength of the counter-rotating vortex pairs (CRVP) that generated by the interaction of individual cooling jet and the mainstream. For LDSA shape of hole, the CRVP are almost disappeared. The LDSA shape has shown a highest value in distribution of spanwise-averaged film cooling effectiveness when the blowing ratio increased to 1.5. It is due to the structure of the LDSA is capable of reducing the momentum of the cooling flow at the vent of the cooling holes, thus reduced the penetration of the main stream. (3) The structure of the LDSA can also increase the lateral spread of the cooling flow, thus improves the spanwise-averaged film cooled efficiency.     

Improvement of film cooling performance by trenched holes on turbine leading-edge models

The present study aims to improve cooling performance over the leading edge surface with the high temperature and high thermal stress by the introduction of trenched holes. Three staggered rows of leading-edge film cooling holes with different trench arrangements and hole orientations are included under blowing ratios of 0.5, 1.0, 1.5, and 2.0, compared with round-hole cases. Under the conditions of leading-edge flow patterns and convex curvature, the trenched hole with 2D width plays a role of “protection” of coolant against the impinging hot gas at a large range of blowing ratios. This contributes to the better lateral spread of coolant and cooling performance. Besides, the trenched holes narrow the regions with a high heat transfer coefficient and reduce the detrimental heating on the surface. Compared with round holes, the trenched holes guarantee the downstream coolant coverage and higher cooling performance at a larger inclined angle, in spite of the changed compound angles.     

Influence of secondary hole injection angle on enhancement of film cooling effectiveness with horn-shaped or cylindrical primary holes

Abstract

Film cooling with primary and secondary hole injection is numerically investigated. Effects of primary hole shape and secondary hole injection angle are documented. Each primary hole, either cylindrical or laterally diffused, has two secondary, cylindrical holes located symmetrically about it. Adding secondary holes improves cooling performance. Five cases of different secondary hole injection configuration are analyzed. With a cylindrical primary hole, increasing secondary hole inclination angle provides better cooling; outwardly inclining the secondary holes shows continued improvement. With horn-shaped primary holes, smaller secondary hole inclination angles provide higher cooling at lower blowing ratios; larger secondary hole inclination angles provide higher cooling at higher blowing ratios, and compound-angle secondary hole injection shows no improvement over parallel hole injection.     

Effect of hole configurations on film cooling performance

This study aims to investigate the cooling performance of various film cooling holes, including combined hole, cylinder hole, conical hole, and fan-shaped hole. For film cooling technology, a novel combined hole configuration is first proposed to improve the cooling protection for gas turbine engines. This combined hole consists of a central cylinder hole (an inclination angle of 35°) and two additional side holes (a lateral diffusion angle of 30°). Film holes for four-hole configurations have the same inlet diameter of 8?mm. The adiabatic film cooling effectiveness for each hole configuration is analyzed for varying blowing ratios (M?=?0.25, 0.5, 0.75, and 1.0). Results show that the best cooling performance for the conical and fan-shaped holes is obtained at the blowing ratio of 0.75. In addition, the combined hole configuration provides a more uniform cooling protection and a better cooling performance than the other hole configurations.     

开槽气膜孔结构对气膜冷却和流动特性的影响

运用数值模拟的手段,从流动特性和冷却特性两方面评价了各种开槽气膜冷却孔结构的优劣。从流动的机理揭示了在相同的槽深下,不同的横槽结构对改善气膜冷却效率和流量系数的影响,并比较了在气膜孔出口和入口均开有横槽后对流动和冷却特性的影响。结果表明：开横槽后,气膜孔出口下游的冷却效率得到不同程度的改善,吹风比越大,改善的程度越明显。在横槽下游5D-10D的范围内,冷却效率的改善程度最大;在气膜孔出入口处均开有斜横槽的结构和用圆角过渡气膜孔入口处的横槽均是提高气膜冷却效率和减小气膜孔流动阻力的有效措施,而在气膜孔出口处的横槽用圆角过渡则不利于改善气膜冷却效果。     

Role of gaseous film cooling injector orientation in duct flow: Experimental Study

Experimental investigations are carried out to analyze the effect of coolant injector configuration on overall film cooling performance in a cylindrical test section similar to a rocket combustion chamber. Three different injector orientations are investigated: (i) holes parallel to core gas flow, (ii) holes at a tangential angle to the core gas flow, and (iii) compound angle holes inclined to the wall both in the tangential and azimuthal direction. The objective is to provide a consistent set of measurements for cooling effectiveness within the same test facility with respect to different blowing ratios ranging from 1.69 to 3.9. The results suggest that coolant injection parallel to the axis should be used in situations where far field effectiveness is of concern. The tangential injection, in general, shows lower wall protection compared to other schemes. The results show that the compound angle configuration augments film cooling effectiveness in the near injection regimes. However comparison of the effectiveness values for the compound injectors suggests the existence of an optimum compound angle configuration. The circumferential wall temperature data represent systematic changes in the coolant flow behavior with the change from straight injection to compound angle injection.     

Computational prediction into staggered film cooling holes on convex surface of turbine blade

The purpose of this paper is to predict the film cooling performance of inline configuration of cooling holes in comparison to the staggered arrangement on convex surface. Three‐dimensional computational study for 10° diffused hole (β = 10°, γ = 0°) and compound hole of 10° diffused and 45° with the downstream direction (β = 10°, γ = 45°) film cooling holes were investigated for adiabatic film cooling effectiveness and have been compared with that of simple hole (β = 0°, γ = 0°) film cooling on convex surface. Both the diffused and compound holes showed better film cooling effectiveness than the simple hole in all models. In one row film cooling investigation, the centerline adiabatic film cooling effectiveness of diffused hole is slightly higher than that of the compound hole near the hole trailing edge. In the staggered case, the centerline effectiveness of the compound hole was higher for both two staggered rows and three staggered rows. For the lateral effectiveness investigations of one row, diffused hole showed higher effectiveness compared with the simple hole and the right side of the compound hole while the left side of the compound hole dominated the lateral investigations in all the models. Staggered distribution of diffused and compound holes showed higher protection for the convex surface. The present results are important dissemination in many practical applications of aero engine industry.     

Film cooling characteristics of rows of round holes at various streamwise angles in a crossflow: Part II. Heat transfer coefficients

Measurements of heat transfer coefficient (h) are presented for rows of round holes at streamwise angles of 30°, 60° and 90° with a short but engine representative hole length (L/D = 4). The study began with a single row of holes with pitch-to-diameter ratios of 3 and 6, followed by two inline and staggered rows for each hole spacing and streamwise inclination, which amount to 105 different test cases in addition to the 21 test cases presented on the single hole [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single round hole at various angles in a crossflow: Part I. Effectiveness, Int. J. Heat Mass Transfer, in press; C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single round hole at various angles in a crossflow: Part II. Heat transfer coefficients, Int. J. Heat Mass Transfer, in press]. The present investigation is a continuation of the previous work [Yuen and Martinez-Botas, Parts I and II, in press] with the same test facility, operating conditions (freestream Reynolds number, Re_D of 8563, and blowing ratio, 0.33 ⩽ M ⩽ 2), and measurement technique of liquid crystal thermography and the steady-state heat transfer method, therefore the results presented in the form of h/h₀, which is the ratio of heat transfer coefficient with film cooling to that without, are directly comparable. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The corresponding measurements of effectiveness for the rows of holes are presented in a companion paper [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of rows of round holes at various angles in a crossflow: Part I. Effectiveness, Int. J. Heat Mass Transfer, submitted for publication]. The low effectiveness observed with the 90° holes in the companion paper [Yuen and Martinez-Botas, submitted for publication] and the relatively large heat transfer coefficient presented here, suggest that the normal injection should only be used in situations where shallower holes are not feasible. The combined performance of effectiveness and heat transfer coefficient suggests that the two inline rows are likely to be advantageous in the film cooling of turbine blades with good coverage per unit mass flow of cooling air and lower thermal stresses due to the smaller heat load.