The Department of Defense, specifically the United States Air Force, is seeking innovative solutions for the development of a High Efficiency Fast Icing Cloud Uniformity Characterization System for the AEDC Free-Jet Engine Test Facility. The objective is to create an in situ, continuous, real-time optical method to characterize spray and icing cloud uniformity in a large turbine engine test facility, addressing critical safety and performance issues related to engine testing under icing conditions. This technology is vital for ensuring aircraft reliability in adverse atmospheric conditions, with applications extending to both military and commercial sectors, including fuel spray research and agricultural evaluations. Interested parties must submit their proposals by November 6, 2024, with further details available on the official solicitation website.

## Description

Engine testing under icing conditions including supercooled droplets, supercooled large drops (SLD), and ice crystal ingestion are critical to aircraft safety and performance. Modern jet engines have improved efficiency using lighter turbine blades and closer tolerances of the blades to the engine wall. However, these advancements have also increased the vulnerability of these engines to damage as a result of atmospheric conditions and especially to liquid droplet and ice crystal ingestion. For commercial aircraft, over 200 documented cases of engine power loss while flying at high altitudes, typically at above 22,000 feet, have been attributed to ice crystal ingestion. Military aircraft need to withstand a wide range of atmospheric conditions and must perform under these adverse conditions due to mission requirements. The AEDC Free Jet Engine Test Facility is designed to simulate these atmospheric conditions and test full-scale engines under these conditions with flows up to and exceeding transonic speeds. Advanced optical diagnostics are needed to rapidly and efficiently report the droplet and ice particle uniformity over the area of the free jet flow to facilitate reliable and accurate simulations of actual cloud conditions encountered in flight. Currently, icing cloud uniformity measurements are performed using a metal grid bolted in front of the free jet and allowed to accrete ice on the exposed surfaces during an icing spray. Once a sufficient amount of ice is accreted on the grid, the facility must be shut down and the accreted ice manually measured by technicians using calipers to gauge the ice thickness and determine the cloud uniformity. Cloud conditions will depend on a number of different parameters including airspeed, temperature, cloud water content, and droplet size. Proper calibration is required over the operational range of all these parameters. This process is time-consuming and highly inefficient and, thus, is impractical and cost prohibitive for the continuous operations requirement for the large, simulated-altitude, Free Jet Engine Test Facility at AEDC.An optical method consisting of laser light sheets and detectors or cameras would facilitate rapid acquisition of the spray uniformity data. One approach that has been applied in other facilities is based on light extinction tomography and has been evaluated for such calibrations to provide real-time monitoring of cloud uniformity and density in situ and non-intrusively. The light extinction tomographic reconstruction from a large number of line integrals could provide sufficient resolution to characterize the simulated cloud uniformity. Furthermore, the information would be available in real-time during testing without concerns of foreign object debris (a major concern in these facilities) since the material components of the instrument would be located outside of the flow field. However, other innovative technologies will be considered. Proposed methods need to be able to operate over optical path lengths larger than the 11 ft diameter of the free jet facility and must withstand high noise and vibration levels without losing alignment or functionality. 

## Objective

Develop an in situ, continuous, real time, optical method for characterizing the spray and icing cloud uniformity in a large turbine engine Free Jet Engine Test Facility for flow speeds to transonic. 

## Phase I

The Phase I effort should develop a concept and demonstrate a smaller scale working model to prove the feasibility of the proposed approach. The feasibility should be evaluated through detailed theoretical analysis and reviews of the tomographic reconstruction algorithms and provide determination of any limitations due to the long optical path length to ensure the method can be used in such a large high-speed facility with potential airflow density fluctuations that could cause beam steering. Careful reviews of the previous work on laser light extinction tomography should be conducted to determine the minimum number of transmitters and detectors needed to provide sufficient spatial resolution over the free jet flow field, or similar reviews and analysis if another concept is proposed. Estimations of the resolution and accuracy of the uniformity measurements need to be provided to determine whether or not the approach meets the test field requirements before advancing to the Phase II prototype development. Visits to the ADEC facility to evaluate the installation requirements are encouraged. The Phase I effort is expected to culminate in a conceptual design that will meet the system requirements and provide a detailed plan for the development of a prototype system during the Phase II effort.

## Phase II

Develop, demonstrate and deliver a fully operational prototype system that includes the hardware and tomographic reconstruction algorithms able to provide sufficient spatial resolution to characterize the cloud uniformity over the 11-foot diameter reject flow field. The demonstration should be conducted in the AEDC Free Jet Engine Test Facility (or another relevant environment acceptable to the Air Force) sufficiently early to allow refinements, as necessary. An operator&rsquo;s manual with detailed instructions, operational training and a spare parts list should be a part of the Phase II effort.

## Phase III: Dual Use Applications

Spray uniformity measurements are needed over a very wide range of applications for sprays with diameters from less than 1 to 12 feet. The technology developed should be scalable to address this wide range of both military and commercial applications. For example, aircraft icing research facilities still acquire spray uniformity measurements using icing grids which are very time-consuming and expensive to implement. Commercial applications would include fuel spray research and quality control studies, agricultural spray system evaluations, and a wide range of other applications.

High Efficiency Fast Icing Cloud Uniformity Characterization System for the AEDC Free-Jet Engine Test Facility

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