Design Exploration of Low-Speed Wind Tunnel for Improved Flow Characteristics with STAR-CCM+ and Optimate+

Aerodynamic Department LWTE AWTE 2 RUAG Aviation

LWTE Test section Test Section 7m x 5m x 12m (21x15x36ft) Max. 68 m/s, Ma=0.2 3 RUAG Aviation

Reference Wind Tunnel Tests www.aerodynamics.ch 4 RUAG Aviation

Large Wind Tunnel Emmen LWTE Facility built 1945 5 RUAG Aviation

Large Wind Tunnel Emmen LWTE facility built 1945 continuous improvements - flow straightener (Darchem honeycomb), 2001 - controlled systems, model manipulators (sensors and software), 2006-2008 - data acquisition, 2006 - master control program, 2007 - upgrade hydraulic supply, 2010 - acoustic capability 2014 6 RUAG Aviation

LWTE Airline test section nozzle flow straightener honeycomb 3200kW CR fan Mesh 8 RUAG Aviation

LWTE Airline Evaluation plane for flow homogeneity Mesh 9 RUAG Aviation

Flow Quality Mesh in corner 3 Velocity in test section 21 Iterations 10 weeks of wind tunnel occupancy 10 RUAG Aviation

Motivation 2016 Fan blade redesign and replacement Fan blade design life reached Improved flow distribution behind the fan, less velocity deficit in the wake of the nacelle Mesh refurbishment necessary due to age Reduction of pressure losses Compensate for pressure losses due to possible installation of a heat exchanger which stabilizes flow temperatures Improve wind tunnel efficiency and maximum speed Use CFD as a tool to improve efficiency of optimization 11 RUAG Aviation

LWTE Optimization - Background Transient simulation of full wind tunnel 3D unsteady Segregated flow solver Constant density air SST k-ω turbulence model All y+ wall treatment Rigid body motion for propellers No mesh present in corner 3 Steady optimization simulations 3D steady Use transient results for BCs Specified Pressure Outlet @ Atmospheric Pressure Specified Velocity Inlet 12 RUAG Aviation

Simulation Experiment LWTE Optimization - Background 13 RUAG Aviation

LWTE Optimization - Background Parameters (170) Inertial resistances in porous baffle equation p = ρ(α v n + β)v n Discrete set of 34 values corresponding to known mesh configurations Design goals Maximize flow uniformity in test section Minimize pressure drop 17 10 14 RUAG Aviation

LWTE Optimization - Background Transient simulation of full wind tunnel 70 M trimmed cells Steady optimization simulations 16 M Trimmed cells 15 RUAG Aviation

LWTE Optimization - Background Reporting 1000 iteration moving averages of max dynamic pressure difference and pressure drop Convergence 25 Pa 1000 iteration asymptotic stopping criteria for pressure drop 0.01 Pa 1000 iteration asymptotic stopping criteria for max dynamic pressure difference 12000 max iterations flags design as error due to lack of convergence if reached 16 RUAG Aviation

LWTE Optimization - Results 0.145 0.07 0.1 0.1 0.133 0.044 0.034 0.021 17 RUAG Aviation

LWTE Optimization - Conclusion In 1 week of optimization the maximum difference in the test section dynamic pressure reduced from 13% of mean to 2.1% of mean Identified novel concepts for mesh design with potential to significantly reduce pressure drop with good uniformity Additional runs are expected to continue to find improved designs More thorough validation of the CFD model to LWTE Update the CAD to correctly represent the propeller geometry Include flow straightener Ensure mesh and time step independence Incorporate a pressure drop constraint that would allow the addition of the heat exchanger Pareto optimization would represent a valuable approach to this problem 18 RUAG Aviation