SBIR-STTR Award

The efficiency of electric motors and generators operating with high rotor surface speeds is reduced due to viscous shear and aerodynamic effects. These losses are generally referred to as "windage loss." In some specific, high speed machines of particular interest to the aircraft community, it has been suggested that the losses could be as high as 10% to 15% of rated power. For the case of liquid cooled machinery in modern tactical aircraft, heat input at these levels can result in unacceptable fuel temperature rise, leading to undesirable performance tradeoffs. In this Phase I SBIR project, Xdot Engineering and Analysis proposes to investigate two innovative approaches for directly reducing these windage losses. The first is especially relevant to switched-reluctance machines such as those for aircraft applications. The second is relevant for a wider class of machines. Both can be applied with minimal or no change to the overall electrical/magnetic design of the machine. Applied individually, or in synergistic combinations, the aim is to achieve a reduction in windage power loss of at least a factor of 2, with a goal of an order of magnitude or more.

Keywords:
Windage Loss Reduction, Taylor Vortex Control, Coupled Fluid-Structural Interaction

Designers of modern, high speed electrical power generation machinery have had great success in increasing the overall system efficiency of these machines over the past few decades. These increases in efficiency are extremely important for applications in modern tactical aircraft, where any losses ultimately heat the fuel. As machine power levels increase to meet aircraft system demands, fuel temperature limits can lead to undesirable tradeoffs. One power loss mechanism that designers have not significantly reduced is windage losses. During Phase I, Xdot Engineering and Analysis analytically showed the feasibility of a new approach for reducing windage losses. During the Phase II effort, Xdot will optimize this approach and demonstrate optimized implementations in a full scale test rig at relevant speeds. The optimization effort will be performed using a CFD analysis that will be validated with new experimental windage loss data generated during the Phase II effort. The experimental portion of the project will be performed using a new windage loss test rig designed specifically to provide accurate rotor windage loss measurements at speeds of up to 60,000 RPM with full scale test hardware.

Benefit:
The proposed Phase II effort will end with the demonstration of an optimized windage loss reduction technology suitable for use in a variety of high speed, electrical rotating machinery. This new windage loss reduction technology will help these machines meet increasingly challenging efficiency and total system power loss targets. The new Xdot technology does not increase system weight, is expected to have a reasonable integration cost, and is applicable to both induction and permanent magnet machines, including secondary or auxiliary power units, as well as main propulsion engine driven starter/generators. It also offer synergistic benefits with regards to rotor cooling. The effort to achieving this end goal will also include the generation of a high quality database of experimental windage loss measurements that is not currently available in the open literature, as well as a new validated design tool/module to help future machinery designers evaluate windage losses in this class of machinery. The initial commercial application of the new windage loss reduction technology is expected to be a commercial direct-drive compressor currently under development by a large original equipment manufacturer. A range of other commercial applications, including other high speed compressors, and waste heat energy recovery turbine generators are also being considered. Opportunities to apply the technology to electrical starting and generating machinery of specific Air Force interest will also continue to be pursued.

Keywords:
Windage Loss Reduction, Cfd Analysis, Windage Power Loss Testing