March 6 - 8, 2017 | Berlin
LEADING ENGINEERING SIMULATION CONFERENCE
Lilium Aviation is a German start-up which develops, manufactures and distributes the worlds first all-electric vertical take-off and landing jet. The revolutionary efficient and patented distributed propulsion system allows ranges of 500km at top speeds exceeding 350km/h.
The propulsion system of the "Lilium Jet" consists of 36 distributed electric fans, mounted in a movable flap system. The flaps are ducting the fans, which allows for maximum efficiency and extreme low noise emission during cruise flight. Nevertheless, the quite high geometric complexity including the fans in a movable flap at high speeds limits the overall concept evaluation to electric fans with a lower number of rotor and stator blades. In order to evaluate arbitrary complex fan systems, a new workaround is derived in the framework of the commercial CFD tool STAR-CCM+®.
First, the fans are investigated separately by employing a Multi-Reference-Frame (MRF) approach. A novel and complete automatic turbo slicing procedure is derived
and applied in order to decrease the optimization turn-around time. This makes the application more generic for any fan configuration. It is demonstrated, that a tremendous amount of time can be saved by automatic pre- and post-processing for estimating the desired propeller curves.
Next, the propeller curves are used to apply the Virtual Disk Model (VDM) in terms of the Blade Element Method (BEM) on an isolated flap with three propellers. By doing so, the flap can be optimized with respect to a drag minimum at a given lift and fixed cruise flight conditions.
The results obtained are used to evaluate the overall aircraft concept efficiently in cruise flight mode with a new minimum of evaluation time. Reference simulations made
with a straightforward mass flow boundary conditions are provided.