Session: 01-13 Modeling, Simulation and Validation IV

Paper Number: 100547

100547 - Fluid Dynamic Loss Model With Wide Applicability for Aeroengine Transmission Gears 

In high-speed gear systems for aeroengines, it is important to reduce fluid dynamic loss, which account for the majority of power loss, to improve fuel economy. For reasonable loss-reduction and the standardization of low-power-loss designs, a fluid dynamic loss model with wide applicability is needed. However, there are few example of a loss model considering the effect of gear shroud (gear enclosures, which is effective for loss reduction) on oil dynamic loss.

Therefore, in this study, a loss model was constructed based on the understanding of the fluid dynamic loss phenomena. The fluid dynamic loss model was divided as “air side-flow loss,” “air pump loss,” “air vortex loss,” “oil-jet acceleration loss,” “oil reacceleration loss,” and “oil churning loss.”

The air side-flow loss was newly defined as a “loss due to flow being pushed out at the into-mesh part, passing beside the gear mesh, and sucked in at the out-of-mesh part.” The air side-flow loss is presumed to be the loss due to the airflow resistance of the gear teeth and was modeled using the aerodynamic drag coefficient. The air pumping loss was newly defined as a “loss due to the flow passing through the tip clearance and backlash of the gear.” The air pumping loss is modeled as the loss owing to the acceleration of air at the tip clearance and backlash from the analogy of the oil-jet acceleration loss. The air vortex loss was newly defined as a loss caused by “vortices generated in the tooth valley of the gear.” In the air vortex loss model, the loss experimental equation of the conventional research was rearranged using “rotational moment coefficients.” The oil-jet acceleration loss was defined as “the loss when oil supplied into the gear mesh is accelerated to the gear peripheral speed” from conventional researches. The oil-jet acceleration loss was calculated from the theoretical equation for the conservation of momentum of oil jet. The oil reacceleration loss is newly defined as “a loss that occurs when oil that has reflowed into the gear mesh is accelerated by the gear.” The oil reacceleration loss was modeled based on the oil-jet acceleration loss, assuming that the mass flow rate of the oil re-entering the gear mesh is proportional to the oil supply flow rate. The oil churning loss was newly defined as a loss caused by “a flow in which an air vortex generated in the tooth valley involve oil particles.” The oil churning loss model was modeled as an increase in the apparent air density owing to the dispersion of oil particles in the air. The loss reduction rate of air vortex loss by shrouding was defined as a shroud coefficient from a conventional research. The effect of the shrouding on oil dynamic loss was newly defined as the reciprocal of the shroud coefficient from a dimensionless evaluation.

Each element of the fluid dynamic loss model was validated by experimental results using a newly developed experimental loss classification method or numerical simulation results using a newly developed numerical loss classification method. The loss model was validated under the following conditions: change in the rotational speed, change in the oil supply flow rate, different gear aspect ratios, and different shroud shapes. To demonstrate the effectiveness of the loss model for low-power-loss design, the influence of design parameters was studied. In addition, gear aspect ratio and shroud shape were used as representative parameters and their optimization was carried out (the gear aspect ratio is tooth width / gear diameter, a parameter “tooth width times the square of gear diameter” was fixed because tooth surface strength and weight were proportional to the parameter). The results show that considerable reduction of power loss is reasonably possible.

Presenting Author: Hidenori Arisawa Kawasaki Heavy Industries, Ltd.

Presenting Author Biography: Hidenori Arisawa is a manager of Energy System Research Department at Technical Institute of Kawasaki Heavy Industries, Ltd. He received a master's degree from Nagoya University. He is engaged in CFD simulation and the experiments on heat and oil management in gear systems of aircraft engines.

Authors:

Hidenori Arisawa Kawasaki Heavy Industries, Ltd.
Mitsuaki Tanaka Kawasaki Heavy Industries, Ltd.
Hironori Hashimoto Kawasaki Heavy Industries, Ltd.
Tatsuhiko Goi Kawasaki Heavy Industries, Ltd.
Takahiko Banno Kawasaki Heavy Industries, Ltd.
Hirofumi Akahori Kawasaki Heavy Industries, Ltd.