N21A-T017 TITLE: Compact Electric Compressors for Aerospace Applications
RT&L FOCUS AREA(S): General Warfighting Requirements
TECHNOLOGY AREA(S): Air Platforms; Weapons
OBJECTIVE: Develop, build, and test a compact and reliable electric compressor for aerospace applications including a fast, compact controller. The compressor must be able to operate in realistic aircraft environments and must not require an external cooling system. Size, Weight, and Power (SWaP) have to be optimized with respect to given performance requirements.
DESCRIPTION: Many aerospace applications such as active flow control (AFC) require compressed air. Often, compressed air is bled and routed from engines, which requires additional hardware, thermal management systems, plumbing and margins on engine sizing. Compact electric compressors offer an alternative to this approach. Many advances in electric compressor technology have been achieved in recent years (e.g., bearing technology, size and efficiency of electric components, materials). However, the technology has not been fully utilized on aircraft. The goal of this STTR topic is to design a compact electric compressor that can withstand the harsh environment of a military aircraft such as vibration, varying ambient conditions, and air pollution.
The design of a compact electric compressor is challenged by conflicting engineering aspects. For example, minimizing the size and weight of a compressor is limited by thermal requirements, bearing design, and vibration tolerances. Many ground-operated systems require a separate cooling system for higher compression ratios. Such a system is undesirable for aircraft operation due to additional weight, volume, and power impact. Additionally, such a compressor needs to be reliable with low maintenance requirements.
Compact compressors can be an enabling technology for AFC systems. Future applications, as well as recent applications such as download alleviation on the V-22 and side force increase on a vertical tail, can directly benefit from compact compressors that are integrated near the location of AFC application. Performance losses and weight impacts can be minimized compared to using engine bleed air. Dedicated compressor systems would also be relevant for future electric or hybrid electric systems.
The compact electric compressor system (including controller) should be conceptually designed and supported by analysis to achieve a pressure ratio of at least 2 operating at sea level and high/hot conditions [Ref 6]. The compressor must not require an additional active cooling system (e.g., liquid cooling with external heat exchanger). The available mass flow rate should be of the order of 1 lbm/s. The volume and weight need to be minimized. Furthermore, the compressor needs to withstand typical military aircraft vibration levels set forth in MIL-STD-810. An overall system assessment of the proposed design should also address the required filtration system.
Demonstration of the performance objectives along with preliminary assessments of unit robustness in realistic environments will be considered the criteria for success.
PHASE I: Complete a feasibility study of a concept for a compact electric compressor system (including controller) that outlines an overall design required to meet the topic objectives and the development of a realizable plan for the manufacturing and testing of the components in Phase II.
PHASE II: Address any required design updates/revisions to achieve the performance objectives. Build the compressor system (including controller) and test for airflow performance (i.e., predicted and actual compressor curves); different ambient conditions (pressure and temperature); vibration per MILSPEC requirements; and sensitivity to dirt ingestion and containment of hub failures.
PHASE III DUAL USE APPLICATIONS: Opportunities will be sought to ground- or flight-test the complete compressor system in realistic conditions to confirm performance, reliability, lifetime, and maintenance requirements. These tests should be as close to a certification type testing as possible. Subsequent activities will then focus on the development of methods/approaches to optimize component manufacturing and reduce overall cost.
AFC technologies have been demonstrated in relevant environments within the commercial sector. Most notably, the Boeing Co. flew an Eco-Demonstrator aircraft where the vertical tail was enhanced with an array of sweeping jets. This flight test proved the performance benefits provided by AFC, with the tail and rudder achieving greater directional control than an unactuated variant. Integration of the actuator arrays, however, was not very straightforward as a result of having to route pneumatic systems from either the main engines or the aircraft auxiliary power unit. Compact electric compressors will enable pneumatic AFC systems independent of engine bleed air by providing compressed air sources. This technology will also be suitable for electric, hybrid electric, and other types of aircraft. Moreover, success of this STTR topic will provide inroads to small businesses for the supply of these enabling components.
KEYWORDS: Compact electric compressor; active flow control; AFC; aircraft subsystems