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.     

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 approach to film cooling effectiveness over a plate surface with coolant impingement

The aim of the present study is conducting the numerical approach to a combination of internal jet impingement and external film cooling over a flat plate. A multi-block three-dimensional Navier-Stokes code, CFX 4.4, with k-e turbulence model is used to simulate this complicated thermal-flow structure induced by the interaction of coolant jet and hot cross mainstream. By assuming the adiabatic wall boundary condition on the tested film-cooled plate, both the local and the spanwise-averaged adiabatic film cooling effectiveness are evaluated for comparison of the cooling performance at blowing ratios of Br=0.5, 1.0, and 1.5. Film flow data were obtained from a row of five cylindrical film cooling holes, inclined in angle of 35?and 0?in direction of streamwise and spanwise, respectively. The film cooling hole spacing between adjacent holes is 15 mm for all the holes. Before the coolant flow being injected through individual cooling hole then encountered with the mainstream, an impingement chamber containing an impingement plate with 43 holes is located on the path of coolant flow. Present study also focused on the effect of impingement spacing, 10mm, 20mm, and 30mm. Compare the results, we find the impingement jet has a significant effect on the adiabatic film cooling effectiveness. As the coolant impingement spacing is fixed, results indicated that higher blowing ratio would enhance the local and the spanwise-averaged adiabatic film cooling effectiveness. Moreover, neither uniform nor parabolic distribution of pressure distribution are observed within the coolant hole-pipe.     

Experimental Study on Impingement and Film Overall Cooling Characteristics of Turbine Shroud

Based on the variable characteristics of the actual operating conditions of the turbine shroud and the purpose of improving the cooling effect of the turbine shroud,this paper builds a test system of the impingement-film cooling shroud with two gas inlet angles(90°,167°).The effects of film cooling hole arrangement,gas inlet angle,blowing ratio(0.7,1.0,1.5,2.0,2.5,3.0)and temperature ratio(1.2,1.3,1.4,1.5,1.6)on the cooling characteristics of the impingement-film cooling shroud were experimentally studied by infrared temperature measurement technology,especially the effects of gas inlet angle and temperature ratio.The results showed that the film covering effect of the film cooling hole vertical or the same direction of the high-temperature gas incoming flow is better than the film covering effect of the reverse direction with the incoming flow,and the optimal arrangement of film cooling holes can improve the cooling effectiveness of the shroud.Compared with 90°intake gas,the film coverage area on the shroud surface of the 167°intake gas is expanded,and the surface average overall cooling effectiveness is increased by 1.03%to 12.6%.The overall cooling effectiveness of turbine shroud increases with the increase of blowing ratio,which increases the flow rate and pressure of cooling gas,and the corresponding increase rate is between 1.04%and 9.96%.However,the increase in the temperature ratio increases the mainstream heating capacity,resulting in a decrease in the cooling effectiveness of the shroud,with a maximum reduction rate of 11.04%.     

The Impingement Heat Transfer Data of Inclined Jet in Cooling Applications: A Review

On the impingement heat transfer data,the experimental studies of air and liquid jets impingement to the flat surfaces were collected and critically reviewed.The oblique impingements of both single circular and planar slot jets were considered in particular.The review focused on the surface where the jet impingement cooling technique was utilized.The nozzle exit Reynolds numbers based on the hydraulic diameter varied in the range of 1,500–52,000.The oblique angles relative to the plane surface and the dimensionless jet-to-plate spacing vary in the range of 15°–90°and 2–12 respectively.The review suggested that the magnitude of maximum heat transfer shifted more for air jets compared with the liquid jets.The drop in the inclination angle and the jet-to-plate separation led to the increase in the asymmetry of heat transfer distribution.The displacement of maximum Nusselt number(heat transfer)locations was found to be sensitive to the inclination angle and the smaller jet-to-plate distance.Also,the Nusselt number correlations proposed by various researchers were discussed and compared with the results of the cited references.     

Cooling Performance of an Impingement Cooling Device Combined with Pins

Experimental study and one dimensional model analysis were conducted to investigate cooling performance of an integrated impingement and pin fin cooling device. A typical configuration specimen was made and tested in a large scale low speed closed-looped wind tunnel. Detailed two-dimensional contour maps of the temperature and cooling effectiveness were obtained for different pressure ratios and therefore different coolant flow-rates through the tested specimen. The experimental results showed that very high cooling effectiveness can be achieved by this cooling device with relatively small amount of coolant flow. Based on the theory of transpiration cooling in porous material, a one dimensional heat transfer model was established to analyze the effect of various parameters on cooling effectiveness. It was found from this model that the variation of heat transfer on the gas side, including heat transfer coefficient and film cooling effectiveness, of the specimen created much more effect on its cooling effectiveness than that of the coolant side. The predictions of the one-dimensional mode were compared and agreed well with the experimental data.     

Numerical Simulation Study on Cooling Characteristics of a New Type of Film Hole

A new type of film cooling hole with micro groove structure is presented in this paper.Based on the finite volume method and the Realizable k-εmodel,the film cooling process of the hole in a flat plate structure is simulated.The surface temperature distribution and film cooling effect of different film cooling holes were analyzed.The effects of micro-groove structure on wall attachment and cooling efficiency of jet were discussed.The results show that under the same conditions,the transverse coverage width and overall protective area of the new micro-groove holes are larger than those of the ordinary cylindrical holes and special-shaped holes.Compared with ordinary holes,the new micro-groove holes can better form the film covering on the surface and enhance the overall film cooling efficiency of the wall.For example,when the blowing ratio M=1.5,the effective coverage ratio of micro-groove holes is 1.5 times the dustpan holes and is 8 times the traditional cylindrical holes.It provides reference data and experience rules for the optimization and selection of advanced cooling structure of high performance aero-gas engine hot-end components.     

Leading edge film cooling enhancement for an inlet guide vane with fan-shaped holes

This paper describes the improvement of leading edge film cooling effectiveness for a turbine inlet guide vane by using fan-shaped film cooling holes. The modification details are presented in comparison with the base-line configuration of cylindrical holes. Numerical simulations were carried out for the base-line and modified configurations by using CFX, in which the κ-ε turbulence model and scalable wall function were chosen. Contours of adiabatic film cooling effectiveness on the blade surfaces and span-wise distributions of film cooling effectiveness downstream the rows of cooling holes interested for the different cooling configurations were compared and discussed. It is showed that with the use of fan-shaped cooling holes around the leading edge, the adiabatic film cooling effectiveness can be enhanced considerably. In comparison with the cylindrical film cooling holes, up to 40% coolant mass flow can be saved by using fan-shaped cooling holes to obtain the comparable film cooling effectiveness for the studied inlet guide vane.     

Research on cooling effectiveness in stepped slot film cooling vane

As one of the most important developments in air cooling technology for hot parts of the aero-engine,film cooling technology has been widely used.Film cooling hole structure exists mainly in areas that have high temperature,uneven cooling effectiveness issues when in actual use.The first stage turbine vanes of the aero-engine consume the largest portion of cooling air,thereby the research on reducing the amount of cooling air has the greatest potential.A new stepped slot film cooling vane with a high cooling effectiveness and a high cooling uniformity was researched initially.Through numerical methods,the affecting factors of the cooling effectiveness of a vane with the stepped slot film cooling structure were researched.This paper focuses on the cooling effectiveness and the pressure loss in different blowing ratio conditions,then the most reasonable and scientific structure parameter can be obtained by analyzing the results.The results show that 1.0 mm is the optimum slot width and 10.0 is the most reasonable blowing ratio.Under this condition,the vane achieved the best cooling result and the highest cooling effectiveness,and also retained a low pressure loss.     

Numerical investigation of heat transfer coefficient in a low speed 1.5-stage turbine

The paper numerically investigated the heat transfer coefficients over the rotating blades in a 1.5-stage turbine. The hexahedral structured grids and k-ε turbulence model were applied in the simulation. A film hole with diameter of 0.004 m, angled 36°and 28° tangentially to the suction side and pressure side in streamwise respectively, was set in the middle span of the rotor blade. Simulations are done at three different rotating numbers of 0.0239, 0.0265 and 0.0280 with the blowing ratio varying from 0.5 to 2.0. The effects of mainstream Reynolds number and density ratio are also compared. Results show that increasing blowing ratio can increase the heat transfer coefficient ratio on the pressure side, but the rule is parabola on the suction side. Besides, increasing rotating number and Reynolds number is positive while increasing density ratio is negative to the heat transfer on both the pressure side and the suction side.     

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.     

Effect of the Chevron Angle on Cooling Heat Transfer Characteristics of Supercritical Pressure Fluids in Plate Heat Exchangers

ABSTRACT

For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, the authors have studied on cooling heat transfer of supercritical pressure fluids flowing in chevron-type plate heat exchangers (PHEs). In this study, to examine the effect of chevron angle on cooling heat transfer of supercritical pressure refrigerants, experiments were conducted for HFC134a and HFO1234ze(E) flowing in the PHEs with the chevron angles from 30° to 65°. In the experiments, cooling heat transfer coefficients were obtained in the wide range of bulk fluid enthalpy from vapor-like high temperature to liquid-like low temperature, changing the pressure in the reduced pressure range from 1.01 to 1.2 at the mass flow rates of 7 and 11 kg/min. Especially for the enthalpy region of the pseudo critical point and its vicinity in which good heat transfer appeared, the effect of chevron angle on heat transfer of supercritical pressure fluids was clarified based on the measurements. Furthermore, the effect of chevron angle was examined for the wide angle range from 0° to 90° with estimating the heat transfer coefficient for the angles 0° and 90° from appropriate correlations. Besides, the present data were compared with some conventional heat transfer correlations.     

Flow visualization and film cooling effectiveness measurements around shaped holes with compound angle orientations

Experimental results are presented which describe film cooling performance around shaped holes with compound angle orientations. The shaped hole has a 15° forward expansion with an inclination angle of 35°, but the orientation angles vary from 0° to 30° and 60°. The blowing ratios considered are 0.5, 1.0 and 2.0. Flow visualizations are performed using an aerosol seeding method for single enlarged shaped hole to investigate the interaction between the mainstream and the injectant at the hole exit plane. The adiabatic film cooling effectiveness distributions are measured for a single row of seven shaped holes using the thermochromic liquid crystal technique. Flow visualization reveals the occurrence of hot crossflow ingestion into the film hole at the hole exit plane at a large orientation angle such as 60°. Shaped holes with simple angle injection do not provide substantial improvement in the film cooling performance compared to round holes. However, shaped holes with compound angle injection exhibit improved film cooling effectiveness up to 55% in comparison with round hole data at high blowing ratios.     

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.     

Experimental investigation on the leading edge film cooling of cylindrical and laid-back holes with different hole pitches

Experimental investigation has been performed to study the film cooling performances of cylindrical holes and laid-back holes on the turbine blade leading edge. Four test models are measured for four blowing ratios to investigate the influences of film hole shape and hole pitch on the film cooling performances Film cooling effectiveness and heat transfer coefficient have been obtained using a transient heat transfer measurement technique with double thermochromic liquid crystals. As the blowing ratio increases, the trajectory of jets deviates to the spanwise direction and lifts off gradually. However, more area can benefit from the film protection under large blowing ratio, while the is also higher. The basic distribution features of heat transfer coefficients are similar for all the four models. Heat transfer coefficient in the region where the jet core flows through is relatively lower, while in the jet edge region is relatively higher. For the models with small hole pitch, the laid-back holes only give better film coverage performance than the cylindrical holes under large blowing ratio. For the models with large hole pitch, the advantage of laid-back holes in film cooling effectiveness is more obvious in the upstream region relative to the cylindrical holes. For the cylindrical hole model and the laid-back hole model with the same hole pitch, heat transfer coefficients are nearly the same with each other under the same blowing ratios. Compared with the models with large hole pitch, the laterally averaged film cooling effectiveness and heat transfer coefficient are larger for the models with small hole pitch because of larger proportion of film covering area and strong heat transfer region.     

A Numerical Study on Improving Large Angle Film Cooling Performance through the Use of Sister Holes

The present study evaluates a novel sister hole cooling technique using large inclination angle cylindrical holes simulated numerically. Here, a 55° inclination angle has been applied to simulate more realistic turbine conditions. Two sister holes bound the primary injection hole and are shifted slightly downstream to promote flow adhesion. As a means of determining the validity of the technique, adiabatic effectiveness and vortex flow structures were evaluated at four blowing ratios: 0.2, 0.5, 1.0, and 1.5. The results indicate that the sister hole technique dramatically reduces the primary kidney vortex pair offering significant improvements in effectiveness at all blowing ratios.     

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.     

Film cooling performance and heat transfer over an inclined film-cooled surface at different convergent angles with respect to highly turbulent mainstream

Experiments have been performed to study and obtain the adiabatic-wall film cooling effectiveness and the heat transfer over a film-cooled surface that is made inclined at various angles with respect to a highly turbulent flow. The film-cooled air is injected from a tangential slot. The normal temperature distributions were measured to infer the flow structure and the rate of mixing of film jet with the freestream. The freestream turbulence intensity is controlled to range from 1.0% to 26.4%, the inclination or the convergent angle of the film-cooled surface ranges from 0° to 20°, the blowing parameter from 0.5 to 2.0. It is found that the mixing of the film jet with the freestream is significantly enhanced by both the freestream turbulence intensity and the convergent angle of the film-cooled surface, which leads to the decrease in the film cooling effectiveness and the increase in the heat transfer when the inclination angle of the film-cooled surface is not large. This is attributed to the two competition mechanisms of impinging effect and the stabilization due to acceleration of the mainstream. The normal temperature distribution at several locations along the flow direction is also measured and used to infer the flow structure of the mixing of film jet with the mainstream. More detailed discussion is presented. Correlations for both the film cooling effectiveness and the heat transfer under the film-cooled surface have been very successful and are provided.