Numerical investigation of particle deposition on converging slot-hole film-cooled wall

Numerical research on the dilute particles movement and deposition characteristics in the vicinity of converging slot-hole(console) was carried out, and the effect of hole shape on the particle deposition characteristics was investigated. The EI-Batsh deposition model was used to predict the particle deposition characteristics. The results show that the console hole has an obvious advantage in reducing particle deposition in comparison with cylindrical hole, especially under higher blowing ratio. The coolant jet from console holes can cover the wall well. Furthermore, the rotation direction of vortices near console hole is contrary to that near cylindrical hole. For console holes, particle deposition mainly takes place in the upstream area of the holes.

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.

EXPERIMENTAL MEASUREMENT AND NUMERICAL SIMULATION FOR FLOW FIELD AND FILM COOLING EFFECTIVENESS IN FILM-COOLED TURBINE

Numerical simulation of three-dimensional flow field and film cooling effectiveness in film-cooled turbine rotor and stationary turbine cascade were carried out by using the k- ε turbulence model, and the predictions of the three-dimensional velocities were compared with the measured results by Laser-Doppler Velocimetry （LDV）. Results reveal the secondary flow near the blade surface in the wake region behind the jet hole. Compared with the stationary cascade, there are the centrifugal force and Coriolis force existing in the flow field of the turbine rotor, and these forces make the three-dimensional flow field change in the turbine rotor, especially for the radial velocity. The effect of rotation on the flow field and the film cooling effectiveness on the pressure side is more apparent than that on the suction side as is shown in the computational and measured results, and the low film cooling effectiveness appears on the pressure surface of the turbine rotor blade compared with that of the stationary cascade.

Conjugate calculation of a film-cooled blade for improvement of the leading edge cooling configuration

Great efforts are still put into the design process of advanced film-cooling configurations.In particular,the vanes and blades of turbine front stages have to be cooled extensively for a safe operation.The conjugate calculation technique is used for the three dimensional thermal load prediction of a fim-cooled test blade of a modern gas turbine.Thus,it becomes possible to take into account the interaction of internal flows,external flow,and heat transfer without the prescription of heat transfer ooefficients.The focus of the investigation is laid on the leading edge part of the blade.The numerical model consists of all internal flow passages and cooling hole rows at the leading edge.Furthermore,the radial gap flow is also part of the model.The comparison with thermal pyrometer measurements shows that with respect to regions with high thermal load a qualitatively and quantitatively good agreement of the conjugate results and the measurements can be found.In particular,the region in the vicinity of the mid-span section is exposed to a higher thermal load,which requires further improvement of the cooling arrangement.Altogether the achieved results demonstrate that the conjugate calculation technique is applicable for reasonable prediction of three-dimensional thermal load of complex cooling configurations for blades.

基于光场成像技术的气膜冷却孔几何参数检测

In a high thrust-weight-ratio aero-engine,turbine blades are exposed to extremely high temperature and pressure which sets higher demands in the blade cooling technology.To boost film-cooling effectiveness,an accurate,efficient,and all-sided inspection of film cooling holes is urgently requested to ensure the quality of turbine blades.The tiny size of film-cooling holes adds to extreme difficulties in the inspection process both by contact and non-contact measurement.This paper proposed a non-contact measuring technique to cope with the inspection of turbine blades.A specially designed light-field camera with a small field of view and proper depth of field is applied to resolve a 3D geometry of film cooling holes.The technique uses one light field camera to capture images of the blade surface.3D lightfield reconstruction algoritm is applied and point cloud of the blade is generated.Due to the compactness of the non-contact single light-field imaging system,information inside the holes becomes attainable.By precisely controlling the relative pose of the camera to the blade surface,the device can obtain hole diamter and outlet angle with an accuracy of±0.03mm and±1°17’respectively.The average time consumed for reconstructing one film cooling hole is about 5 seconds.

Machining of a film-cooling hole in a single-crystal superalloy by high-speed electrochemical discharge drilling

Single-crystal superalloys are typical advanced materials used for manufacturing aero- engine turbine blades. Their unique characteristics of high hardness and strength make them exceedingly difficult to machine. However, a key structure of a turbine blade, the film-cooling hole, needs to be machined in a single-crystal superalloy; such machining is challenging, especially considering the increasing levels of machining efficiency and quality demanded by the aeroengine industry. Tube electrode high-speed electrochemical discharge drilling （TSECDD）, a hybrid technique of high-speed electrical discharge drilling and electrochemical machining, provides high machining efficiency and accuracy, as well as eliminating the recast layer. In this study, TSECDD is used to machine a film-cooling hole in a nickel-based single-crystal superalloy （DD6）. The Tagu- chi methods of experiment are used to optimise the machining parameters. Experimental results show that TSECDD can effectively drill the film-cooling hole; the optimum parameters that give the best performance are as follows： pulse duration： 12μs, pulse interval： 30 gs, peak current： 6 A, and salt solution conductivity： 3 mS/cm. Finally, a hole is machined by TSECDD, and the results are compared with those obtained by electrical discharge machining. TSECDD is found to be promising for improving the surface quality and eliminating the recast layer.

LES of rotating film-cooling performance in a 1-1/2 turbine stage

The large eddy simulation method was employed to investigate the film-cooling performance in a low-speed rotor blade of a 1-1/2 turbine stage.The rotor blade height and axial chord length were 99 mm and 124.3 mm,respectively.Two rows of film holes were placed on the rotor blade surface,one each on the pressure and suction surfaces.Each row had three cylindrical film holes with a diameter of 4 mm and a tangential injection angle of 28°on the pressure side and 361 on the suction side.The Reynolds number was fixed at Re=1.92×10^(5)and the coolant-to-mainstream density ratio(DR)was about 2.0.Simulations were carried out for three different rotating speeds of 1800,2100,and 2400 rpm with the blowing ratio(BR)varying from 0.3 to 3.0.The commercial CFD code STAR-CCM+was used to run the simulations using the WALE subgrid-scale model for modelling the turbulence.The results show that on the pressure side,the film coverage and filmcooling effectiveness decrease with increasing rotation number(Ro)and increase with increasing blowing ratio(BR).A higher Ro and lower BR result in a stronger film deflection.The film injection with higher BR produces better film attachment.The film deflects centrifugally where the deflection becomes greater with increasing Ro.On the suction side,the film coverage and film-cooling effectiveness increase with increasing either Ro or BR and a centripetal deflection of the film is observed.The deflection of the film path could be amplified by either increasing the Ro at a constant BR or decreasing the BR at a constant Ro.Increasing the rotation weakens the film deflection towards the hub on the suction surface.Overall,it was found that both rotation number and blowing ratio play significant roles in determining the film-cooling effectiveness distributions of the rotor blade surface.

A numerical study of anti-vortex film-cooling holes designs in a 1-1/2 turbine stage using LES

The primary focus of the present study is to investigate the impact of anti-vortex holes design on the film-cooling performance in a film-cooled rotor blade model using the large eddy simulation method(LES).One row of the film holes was positioned on the pressure surface of the rotor blade.This row had three cylindrical holes(the main hole in the present study)with a diameter(D)of 4 mm and a tangential injection angle of 28 deg.Each main hole supplemented with the addition of two symmetrical side holes(anti-vortex holes),which branch out from the same main hole.Three positions for the anti-vortex side holes were considered;namely:upstream to the outlet of the main hole;in line with the main hole;and downstream of the main hole.The Reynolds number was fixed at Re Z 1.92
105 and the speed of the rotor blade was taken to be 1800 rpm.The blowing ratio varied from 1.0 to 5.0 and the density ratio of coolant to mainstream was 2.0.Compared to the base hole,the film cooling performance of the all anti-vortex cases showed obvious improvement at all blowing ratios.The middle stream side holes and downstream side holes each demonstrated good film cooling performance at all blowing ratios,while the upstream side holes perform well only at a lower blowing ratio.The presence of side holes can restrain the CRVP(counter rotating vortex pairs)intensity of the main hole and reduce the coolant lift-off,improving the film coverage and film cooling effectiveness.The downstream side holes can perform better in reducing the CRVP intensity.

Effect of tube-electrode inner diameter on electrochemical discharge machining of nickel-based superalloy

Nickel-based superalloys are widely employed in modern aircraft engines because of their excellent material characteristics, particularly in the fabrication of film cooling holes. However, the high machining requirement of a large number of film cooling holes can be extremely challenging. The hybrid machining technique of tube electrode high-speed electrochemical discharge drilling(TEHECDD) has been considered as a promising method for the production of film cooling holes. Compared with any single machining process, this hybrid technique requires the removal of more complex machining by-products, including debris produced in the electrical discharge machining process and hydroxide and bubbles generated in the electrochemical machining process. These by-products significantly affect the machining efficiency and surface quality of the machined products. In this study, tube electrodes in different inner diameters are designed and fabricated, and the effects of inner diameter on the machining efficiency and surface quality of TEHECDD are investigated. The results show that larger inner diameters could effectively improve the flushing condition and facilitate the removal of machining by-products. Therefore, higher material removal efficiency, surface quality, and electrode wear rate could be achieved by increasing the inner diameter of the tube electrode.