C om putational Fluid D ynam ics S im u latio n s and Experim ents for R eduction of Oil Churning Loss and W in d a g e Loss in A ero en g in e Tran sm issio n G earsThe demand for power generation capacity has increased considerably due to the electric drive o f cabin air conditioners and commercial aircraft engines. It is estimated that power losses may increase in the accessory gearbox due to generators and pumps that augment fuel consumption. To reduce these losses, a computational fluid dynamics simu lation technique that analyzes oil churning and windage losses was developed and improvements were made to the shrouds of bevel gears, which have large losses in the gearbox. It was revealed experimentally that shrouding reduced losses up to 36% as com pared to unshrouded gears. Pll = Taa> = Frpco = '^2^-{vp -v i)-vp(1) i where P is the power loss loaded on a gear, T is the torque, F is the force, r is the radius, to is the angular rotational speed, m is the mass, t is time, and v is the speed. The subscript a is the oil

In recent years, the demand for power generation capacity has increased considerably due to the electric drive of air conditioners and so on in the engines of civil aircraft. Therefore, it is estimated that power losses may increase in the gearbox because of generators and pumps that in turn augment fuel consumption. To understand the phenomena of losses in the gearbox and to reduce these losses, Computational Fluid Dynamics (CFD) simulation that analyzes oil churning loss and windage loss was developed and improvements were made to the shroud of bevel gears. The CFD agreed with experimental results on a bevel gearbox of a 100-seater aircraft. And, it was shown that the suppression of momentum transfer from the rotating gears to oil clusters is of importance. In addition, it was revealed that the loss was reduced up to 36% compared to non-shrouded gears by shrouding in the experiments. This CFD simulation can be applied to many types of gearboxes that have spur gears, bearings and seals.

Reducing the fluid dynamic power loss for increasing speed is critical for the development of highly efficient high-speed aircraft engine gearing. In this study, the fluid dynamic loss was experimentally performed using a precise friction loss management technique along a vacuum being drawn on the gearbox. The experimental fluid dynamic loss could be classified as either “oil jet acceleration loss and oil reacceleration loss based on the conservation law of momentum for a point mass” or “oil churning loss and windage loss based on the conservation law of momentum for an incompressible continuum.” Windage loss and oil dynamic loss (i.e., the summation of oil jet acceleration loss, oil reacceleration loss, and oil churning loss) were modeled to develop equations for a loss prediction. The equations of the windage loss are pressure loss of flow passing through the side clearance of the gears and energy loss caused by the vortex generation in the cavity between tooth valleys. Oil dynamic loss was determined by multiplying the oil jet acceleration loss by an empirical coefficient. The results of the loss prediction equations agree with the experimental results, demonstrating the validity of the proposed model of the fluid dynamic loss.

The requirements for general aero-engines are becoming increasingly severe to achieve higher efficiency and lower emission. The Open Rotor Engine is one of the next-generation aero-engine concepts expected to satisfy these requirements. The Open Rotor Engine has a set of counter-rotating unducted fans to increase the propulsion efficiency. A 20,000 hp class differential planetary gear system is suitable for driving these counter-rotating fans. To realize a 20,000 hp class differential planetary gear system, there are some design challenges to be accomplished 1) large power (20,000 hp class), 2) sufficiently small and light to fit an engine (envelope), 3) high transmission efficiency over 99.5%, 4) precise misalignment control for gears and bearings, 5) high reliability (50,000 hour MTBF). At Kawasaki Heavy Industries, Ltd., development of the Open Rotor Power Gearbox started in 2007. The purpose of this development is to establish a design practice for the 20,000 hp class gear system and to demonstrate that its readiness level (TRL) is appropriate for whole-engine development. In this development, various state-of-the-art simulation technologies such as lube oil flow CFD, FEA, and tooth contact analysis were fully utilized to optimize the design. Details of the design, fabrication, and validation tests of a full-scale prototype up to 2012 were presented at the IDTC/CIE in 2013. This paper presents a summary of the previous activity and subsequent works and achievements as a final report.

No abstract