AQUASENSE - Research and Validation of a Prototype for Simultaneous LWC/IWC Detection in Icing Wind Tunnels

Motivation

The icing of aircraft components (such as wings, engines or sensors) contributes to a significant proportion of aircraft accidents, which in some cases lead to many casualties. In addition to flow velocity and air temperature, the liquid water content, so-called LWC (Liquid Water Content), and the frozen water content, so-called IWC (Ice Water Content), are essential parameters that influence the type and speed of icing. 

Large water droplets with a diameter of more than 2 millimeters, so-called Supercooled Large Droplets (SLD), pose a major threat. They remain liquid due to the lack of condensation nuclei at below freezing point temperatures, and a part of them instantly freezes when it hits the aircraft surface.

In order to experimentally readjust these real icing phenomena - and thus to test and optimize aircraft systems such as de-icing systems - devices which can reliably, reproducibly and uniformly ensure these environmental conditions across cross-sectional tests are therefore required. 

Globally, there are a number of facilities, such as the NASA Glenn Research Icing Tunnel, the CIRA Icing Wind Tunnel and the new RTA Icing Wind Tunnel, which meet these requirements with regard to the necessary actuators for conditioning. 

In order to certify aircraft systems, these facilities must comply with the current FAA and EASA aviation regulations, which require stable and reproducible detection of icing-related parameters (including LWC and IWC) across cross-sectional tests. Due to the lack of apt measuring technology, today these specifications can only be met to a limited extent.

Objectives

• To develop a photoacoustic sensor for LWC/TWC detection.
• To modify FHJ icing wind tunnel.
• To modify RTA climatic wind tunnel.

Content

Within the AquaSense framework, a method for the simultaneous detection of both the aggregation state and concentration of water in flowing media, specifically for application in high temporal resolution icing wind tunnels, will be investigated for the first time in order to test, optimise and certify aircraft systems under defined icing conditions. 

A photoacoustic spectroscopy based prototype will be developed and tested under different operating conditions in the RTA Icing Wind Tunnel and the FHJ Icing Wind Tunnel.

Methodology

In order to fulfill the required measurement quality (temporal resolution and concentration) with regard to the LWC and IWC, AquaSense will investigate a procedure based on highly accurate photoacoustic spectroscopy (PAS) and set up a prototype. This will be achieved, on the one hand, by calculating LWC reference values under the same environmental conditions integral measuring methods (i.e. Blade method, Rotating Cylinder method).

On the other hand, an established sensor approach based on the Hot Wire (HW) principle will be used to verify the LWC/IWC. Finally, the results will be compared with numerical simulations.
The real-time measurements of the LWC and IWC are to be carried out in accordance with the Aerospace Recommended Practice Guide, "Calibration and Acceptance of Icing Wind Tunnels" (SAE ARP 5905). The aim is to further increase international acceptance of national icing wind channels and to ensure conformity in aviation certification in the future.

Expected results

Aeroacoustic design of a PAS resonator and design/manufacture of the resonator, including the cavity cylinder and mounting adapter under the VWS production aspects with consideration of connection, branching off and mounting of the measuring sensor and the integration of a heating system. 

Adaptation of the existing spray nozzles/conversion of the RTA IWT for SLD testing, and adapting/assembling the measuring framework for incorporating all the measuring sensors in the RTA IWT, as well as the measuring technology/hardware and data logging of the PAS prototype and the HW research sensor, have been prepared for the changed environmental conditions in the RTA IWT. 

Extensive statistical evaluation of the determined LWC/IWC values of all measuring methods (PAS prototype, in-house HW research sensor, WCM-2000, BM, RCM) for all operating states in the FHJIWT and RTA IWT, and validation with analytical/numerical results taking into account measurement uncertainties have been completed.

• FH JOANNEUM GmbH - Coordinator
• AVL List GmbH
• Rail Tec Arsenal Fahrzeugversuchsanlagen GmbH

Funding program: TAKE OFF