Investigation Of The Flow And Heat Transfer Characteristics Inside The Contra-Rotating Turbine Disc Cavity

Contra-rotating turbine is the turbine structure in which two adjacent disks rotate in opposite directions. Such contra-rotating turbines could be used to drive the contra-rotating fans of future generations of ultra-high-bypass-ratio engines. This has the advantage of requiring one fewer row of stator nozzles, thereby reducing the weight and size of the engine. And an additional advantage is that contra-rotating turbine structure can reduce the gyroscopic moment produced during maneuvering flight. Contra-rotating turbine has become one of the top research aspects in high-performance gas turbine technology. Compared with the traditional rotating turbine structure, the contra-rotating disc cavity is a novel rotating disk cavity structure. The internal flow and the heat transfer characteristics induced by relative rotation have to be revealed.The methods of experiment and numerical calculation were applied in this paper, and the effects of various parameters on the flow and heat transfer characteristics inside the contra-rotating turbine disc cavity were studied. The research results provide an important theoretical basis for the analysis of engine hot section working conditions under different working status and the monitor of engine performance, as well as ensuring the safety of engine. The main contents are as follows:(1) The wall temperature measurement bench of the contra-rotating turbine disc cavity was designed and constructed.(2)The effect of the change of the disk angular velocity and cooling air mass flow rate on the downstream disk wall temperature were experimentally investigated. The experiment indicated that the averaged heat transfer coefficient on the downstream disk increases and the wall temperature decrease with the increase of downstream disk angular velocity and cooling air mass flow rate.(3) The physical and mathematical models desribing the characteristics of flow and heat transfer in the contra-rotating disk cavity were set up, and the validity of numerical model and methodology was evaluated by comparing the results with the experimental data in the literature. The comparisons of the effectiveness between three turbulence models foe capturing disk wall temperature data were presented,and the RNG k-ε turbulence model is adopted.(4) The features of flow structure inside the closed contra-rotating disc cavity was numerically studied. The results indicate that the flow structure between the closed contra-rotating disks at the same speeds is of a Stewartson type.(5) The characteristics of flow and heat transfer inside the contra-rotating disc cavity with axial center cooling-air inflow are numerically simulated. The effects of the size of axial clearance, cooling air mass flow rate, rotating rate and the disk angular velocity ratio on the pressure distribution, friction torque and convection heat transfer coefficient were analyzed. The results show that:1) The size of axial clearance, the static air pressure in the disc center and the gradient of the static air pressure decrease with the increase of the size of axial clearance. The wall friction torque and the radial temperature gradient do not change obviously with the change of the size of axial clearance. With the increase of the size of axial clearance, the upstream disc wall average Nusselt number increase, while the downstream disc wall average Nusselt number changed little.2) With the increase of, cooling air mass flow rate increase, the negative pressure increases because of the vortex dissipation losses, and the friction moment absolute value of disc walls also increase, the radial temperature gradient decrease. The heat transfer effect of disc walls increases with increasing the cooling air mass flow rate, while the heat transfer effect of downstream disc wall is more obvious than that of the upstream disc wall.3) The positive pressure value region of cavity grows with the increase of rotation speed, so do the pressure and static pressure gradient with the increase of rotating rate. The absolute value of M increase with the increase of rotation speed. The higher of rotation speed, the lower of the upstream disc wall average Nusselt number while the larger of the downstream disc wall average Nusselt number.4) As rotation speed ratio Γ is less than-1, and the rotation speed of the downstream disc is constant, the absolute value of Γ increases with the increase of the rotation speed of the upstream disc. The results are as follows:The positive pressure value of outer cavity is increasing; the absolute value of friction moment of the upstream disc increase while the friction moment of the downstream disc does not change obviously; the radial temperature gradient does not change obviously; the wall average Nusselt numbers of the upstream disc and the downstream disc decrease.5) With-1<Γ<0, the upstream rotational speed is constant, the absolute value of the speed ratio decreases by increasing the absolute value of the downstream disc rotation speed. The result is that:the positive peripheral regions become larger, the downstream disc wall friction torque increases with the little change of, the upstream disc wall friction torque; Average Nusselt number of the upstream and downstream disc increse with the the radial temperature gradient decreasing.