Title: Composite-based multifunctional models for application in cryogenic wind tunnels
(Kompositbasierte Multifunktionale Modelle)

Leader: Airbus Deutschland GmbH, Partners: DLR e.V., ETW GmbH

The main goal of the KoMMod project was to improve the efficiency of wind tunnel tests in ETW, in particular those heading for controlling laminar-turbulent boundary layer transition to enhance environmentally friendly aircraft performance.

The project partners used carbon-fibre reinforced plastics (CFRP) to design and test a laminar half model under cryogenic conditions and flight relevant Reynolds numbers in ETW for the very first time. Commonly, metallic models are used in wind tunnels, particularly at ETW where special maraging steel is required to withstand cryogenic conditions and high model loads. At wind tunnels operated under ambient conditions some model parts made out of plastic or 3D-prints are already in use. The main advantages of these parts are their rapid availability and inexpensive acquisition. In contrast, cryogenic steel models are more expensive and must be manufactured well in advance. The advantage of CFRP models is the efficient lead-time and turn-around time of investigations at flight-relevant Reynolds and Mach numbers in ETW.

For the development of laminar wing geometries, cryogenic tests require procedures to visualize the laminar to turbulent boundary layer transition. At ETW, transition is currently visualized by an artificial temperature change between the model and the surrounding flow, which is initiated by reducing the injection of liquid nitrogen. This procedure influences the Reynolds number as well as the Mach number and generates test data that may need to be reworked. The KoMMod project was designed to improve this procedure and the need to make corrections to the transition data could be drastically improved. The temperature change procedure was replaced by an integrated heating system installed in the CFRP model.

Together with the project partners, a number of CFRP models was designed to provide initial insight in to current manufacturing capabilities. Secondly, the measurement techniques were applied and transferred to CFRP models before test data were collected on a laminar half model in ETW. An important aspect is the development of sensors to detect the transition areas on the models. Colleagues from DLR further enhanced hot-film sensors and temperature sensitive paint before implementing it in the CFRP model. Furthermore, deformation measurements with glass fibres were integrated and provided the opportunity to measure both the shape and the vibration characteristics of the wing under load.

Fibre-composite materials are often used in serial production lines, but rarely in wind tunnel test models. On the one hand, extreme tolerances are defined for wind tunnel models used for flight-relevant investigations and on the other hand, the demand for modern and intelligent aircraft with adaptive wing geometries exists. The materials used for CFRP models are well suited for this topic as they are variable and their characteristics can be individually tailored. Within the KoMMod project also the concept showing camber adjustment for a modern intelligent wing was presented based on a demonstrator.

This work received funding from the German Federal Ministry for Economic Affairs and Energy LuFo V-3/2018-2021 under grant agreement no 20A1704C.

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