Measured overall effusion cooling effectiveness over a wide blowing ratio range using infrared imaging

Experimental investigations were performed on the overall cooling effectiveness η of a flat effusion wall over a wide range of blowing ratio(M=0.47～5.27).The effusion wall had a staggered multi-hole pattern typical of gas turbine combustor application,with a ratio of hole pitch to row spacing P/S=1∶2,a porosity PS/d2=72,and an inclination angle α=30°.The current paper documented distribution of the overall cooling effectiveness on the wall surface,based on infrared imaging of the 2-D surface temperature field.Experimental results indicate:(1) The overall η increases along with the streamwise distance for the wide range of M due to the superposition effect of the multi-row film cooling.(2) The overall η substantially benefits from the multi-hole inside convective cooling.The hole convective cooling not only complements the weakest film protection at initial rows but also helps mitigate the temperature gradient.(3) The overall η increases asymptotically with increasing M,unlike adiabatic η mostly published in the past,which decreased after M reached a specific level.The current work showcased the end cooling outcome jointly driven by the filming cooling mechanism and the hole inside convective cooling mechanism.

Numerical Modeling and Analysis of Grooved Surface Applied to Film Cooling

In order to improve the efficiency of film cooling, numerical investigation was carried out to study the effects of different film-cooled plates on surface heat transfer. Both grooved and non-grooved surfaces were concerned. The modeling was per- formed using Fluent software with the adoption of Shear-Stress Transport （SST） k-ωmodel as the turbulence closure. The coolant was supplied by a single film cooling hole with an inclination angle of 30°. The Mach numbers for the coolant flow and the mainstream flow were fixed at 0 and 0.6, respectively. At three blowing ratios of 0.5, 1.0 and 1.5, the aerodynamic behaviour of the mixing process as well as the heat transfer performance of the film cooling were presented. The numerical results were validated using experimental data extracted from a benchmark test. Good agreements between numerical results and the ex- perimental data were observed. For the film cooling efficiency, it shows that both local and laterally averaged cooling effectiveness can be improved by the non-smooth surface at different blowing ratios. Using the grooved surface, the turbulence intensity upon the plate can be reduced notably, and the mixing between the two flows is weakened due to the reduced turbu lence level. The results indicate that the cooling effectiveness of film cooling can be enhanced by applying the grooved surface.

EXPERIMENTAL INVESTIGATION FOR THE EFFECT OF ROTATION ON THREE-DIMENSIONAL FLOW FIELD IN FILM-COOLED TURBINE

An experimental investigation of three-dimensional flow field in a film-cooled turbine model is carried out by using particle image velocimeter （PIV） in a low-speed wind tunnel. The effects of different blowing ratios （M=1.5, 2） on the flow field are studied. The experimental results reveal the classical phenomena of the formation of kidney vortex pair and secondary flow in wake region behind the jet hole. And the changes of the kidney vortex pair and the wake at different locations away from the hole on the suction and pressure sides are also studied. Compared with the flow field in stationary cascade, there are centrifugal force and Coriolis force existing in the flow field of rotating turbine, and these forces bring the radial velocity in the jet flow. The effect of rotatien on the flow field of the pressure side is more distinct than that on the suction side from the measured flow fields in Y-Z plane and radial velocity contours. The increase of blowing ratio makes the kidney vortex pair and the secondary flow in the wake region stronger and makes the range of the wake region enlarged.

Analysis of Film Cooling Effectiveness on Shaped Hole and Antivortex Hole

Film cooling is introduction of a secondary fluid （coolant or injected fluid） at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immediate region of injection but also downstream region. This paper numerically investigated the film cooling effectiveness on two types of hole geometries which are cut-shaped hole and antivortex hole. The 3D computational geometries are modeled with a single 30 deg angled hole on a flat surface. The different blowing ratios of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5 and k-Epsilon turbulence model are used in this study. A two dimensional distribution of film cooling effectiveness in the downstream region of the cooling hole is performed. A comparison of spanwise averaged effectiveness is also performed in the field starts from center point of hole to X/D=-30.

Numerical Study of Flow and Heat Transfer Characteristics of Impingement/Effusion Cooling

Three-dimensional numerical simulation is carried out to investigate the flow and heat transfer characteristics of impingement/effusion cooling systems. The impingement/effusion holes are arranged on two parallel perforated plates respectively in a staggered manner. Every effusion hole has an inclined angle of 30° with respect to the surface. The two parallel plates are spaced three times the diameter of the effusion hole. The ratio of center-to-center spacing of adjacent holes to the diameter of the effusion hole is set to be 3.0, 4.0 and 5.0 respectively. The flow field, temperature field and wall film cooling effectiveness are calculated for different blowing ratios ranging from 0.5 to 1.5. In general, the wall cooling effectiveness increases as the center-to-center spacing of adjacent holes decreases or the blowing ratio increases.

The cooling performance of three-row compound angle holes on the suction surface of a rotating turbine blade

Experiments were carried out to study the effects of compound angle,hole arrangement,and blowing ratio on the film cooling performance of multiple rows of holes on the suction surface of a turbine blade.The turbine worked at rotational speed of 600 rpm corresponding to the rotational Reynolds number of 5.36
105.Three rows of cylindrical holes arranged in line or in stagger were drilled on the rotor blade suction surface at the streamwise location of 12.4%,17.8%,and 23.2%,respectively.Three compound angles,with the same streamwise angle of 45but different lateral deflection angles of 45,0,and45,were studied.The film cooling effectiveness was obtained using pressure sensitive paint(PSP)technique with average blowing ratios varied from 0.5 to 2.0.The results showed that the application of compound angle changes the jet direction in the near-hole region and makes the film spread laterally.Compared with the film cooling without compound angle,using positive and negative compound angle can improve overall average film cooling effectiveness by about 20%and 25%,respectively.The effects of the secondary flow also can be weakened.A stagger film trajectory arrangement can achieve more uniform film coverage with higher overall film cooling effectiveness.The film trajectory arrangement of a positive compound angle injection is determined by the combined effect of hole arrangement and blowing ratio.While,the film trajectory arrangement of a negative compound angle injection is almost the same as the hole arrangement and nearly does not change with the blowing ratio.

Investigation of the Conjugate Heat Transfer and Flow Field for a Flat Plate with Combined Film and Impingement Cooling

Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.

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%.

Numerical Investigations of Film Cooling Characteristics of Interrupted Slot and Trench Holes on a Vane Endwall

This paper describes film cooling characteristics of the novel combined configuration employing interrupted slot and trench holes on a vane endwall.Interrupted slot,formed by uneven thermal expansion between combustor and high-pressure turbine vane,can improve adiabatic film cooling effectiveness of the leading edge and pressure side-endwall junction by inhibiting the development of horseshoes vortex.Holes embedded into a straight trench were introduced to improve film efficiency comparing to cylindrical holes on vane passage endwall.The influences of lateral pressure gradient,slot coolant and step on crossflow of the hole coolant in trench were mainly discussed.Three dimensional Reynolds-averaged Navier-Stokes equations with shear stress turbulence model(SST k-ω)were used to obtain the flowfields and adiabatic film cooling effectiveness of a cascade model.Four hole blowing ratios M=0.5,1.0,1.5,2.0 and two axial positions X/Cax=–0.05,0 were considered.The coolant crossflow in trench on flat endwall of cascade passage trends to flow towards suction side due to the lateral pressure gradient rather than both sides on flat plate.For combined configuration of interrupted slot and trench holes,the step vortex rolls up hole coolant upstream of trench which changesηdistributions comparing to that on flat passage endwall.Comparing to the cylindrical holes,better film cooling performance can still be obtained when arranging trench holes under high blowing ratios.The influence of hole’s axial positions was also discussed.