INDIAN INSTITUTE OF TECHNOLOGY GANDHINAGAR 33rd AIAA Applied Aerodynamics Conference 22-26 June 2015 Dallas, TX, USA Computational Assessment of Rainfall Effects on Aircraft Aerodynamic Characteristics H. Sharma†, S. Vekaria*, S. Harshe*, M. Singh*, M. Damodaran‡ and B.C. Khoo** INDIAN INSTITUTE OF TECHNOLOGY GANDHINAGAR Discipline of Mechanical Engineering INDIA Temasek Laboratories National University of Singapore Singapore † Graduate Student * Undergraduate Student ‡ Professor and AIAA Fellow ** Director and Professor 25th June 2015

Acknowledgement 1. Temasek Laboratories: Supported the summer internships of the first 4 authors ( IITGN students) at Temasek Laboratories@NUS. 2. Indian Institute of Technology Gandhinagar: Simulations have been carried out at HPCLab@IITGn. Also IIT Gandhinagar have supported for travel of the interns.

Overview Introduction and Motivation Mathematical and Computational Modeling Rainfall Modelling Computational Domain and Meshing Flow Conditions Results and Discussion Conclusion and Future Work

Introduction Experiments have been conducted at NASA for investigating effect of rainfall Discrete Phase Modelling (DPM) approach is used for computational modelling by Valentine and Decker Effect of rainfall is of special interest for low altitude flights Surveillance UAVs fly at low altitude Photograph of wing (with cross-section of NACA 64-210 airfoil) model installed in the NASA Langley 14 by 22 Foot Subsonic Tunnel.

Mathematical And Computational Modeling Navier Stokes Equations Lagrangian Particle Equations Schiller-Naumanns Correlation Schiller, L. and Naumann, A..“A Drag Coefficient Correlation”, VDI Zeitschrift, Vol. 77, pp. 318-320, 1933.

Mathematical And Computational Modeling Particle Modelling Equations 𝐹 𝐷𝑟𝑎𝑔 𝑈 − 𝑣 𝑝 =𝐹𝑜𝑟𝑐𝑒 𝑝𝑒𝑟 𝑈𝑛𝑖𝑡 𝑚𝑎𝑠𝑠= 1 2 𝜌 𝑣 𝑝 − 𝑈 𝑈 − 𝑣 𝑝 𝐶 𝑑 𝜋 𝑑 𝑝 2 4 4 3 𝜋 𝑑 𝑝 3 8 𝜌 𝑝 = 18𝜇 𝐶 𝑑 𝑅𝑒 𝑝 24 𝜌 𝑝 𝑑 𝑝 2 𝑑 𝑣 𝑝 𝑑𝑡 = 𝑣 𝑝 𝑘+1 − 𝑣 𝑝 𝑘 ∆𝑡 𝑣 𝑝 = 𝑑 𝑥 𝑝 𝑑𝑡 = 𝑥 𝑝 𝑘+1 − 𝑥 𝑝 𝑘 ∆𝑡

Raindrop Modelling Rainfall Rate : 1490 mm/hr Injection Grid Injection Grid Parameters Injectors per unit length Mass flow rate at injector Velocity of Injection Location of Injection Grid

Wall Impingement Model   Six possible outcome after Droplet-Wall interaction Bai C., and Gosman A.D., "Development of Methodology for Spray Impingement Simulation," SAE Technical Paper 950283, doi:10.4271/950283 in Proceedings of Society Automation Engineering (SAE),69–87 (1995)

Wall Impingement Model (a) Wetted Wall (b) Dry Wall T12 = Boiling Temperature T23 = Leidenfrost Temperature Wc = Critical Weber Number A = Splash onset coefficient

Thin film modelling Source Terms: Phase interaction Source: OpenFOAM

Thin film modelling Force due to momentum transfer by particles Accounted in momentum equation. Viscous force due to liquid water film. Air Uinf Air Air –Water Interface: Vt = Uinf Water-Wall Interface : Vt = 0 Film Body

OpenFOAM Implementation reactingParcelFilmFoam rainFallFoam Removed: - Combustion Modelling Break up Models Evaporation Utilities : Injection grid generation code. Based on length, width, height, AoA, grid points per unit length and rainfall rate generates the injection grid. Force Calculation: At wet surface, force on the surface is calculated based in pressure from the Eularian field and shear force from the surface film equation

Aerodynamic Configurations Considered Wing with NACA 64-210 airfoil as cross-section z x y Model UAV with wing of NACA 0012 airfoil as cross-section

Computational Domain Wing NACA 64-210 Star-CCM+ OpenFOAM A B C D E F H G I Face ABCD: Inflow Boundary, V : 25 m/s Face ABEF, CGHD, BFGC: Farfield Face EFGH: Outflow Boundary, P = 101325 Pa Face AEHD: Symmetry Plane (Star-CCM+) Farfield (OpenFOAM) Face I: Velocity = 0 m/s Farfield Velocity : 25 m/s Farfield Pressure : 101325 Pa Farfield Temperature : 300K Farfield Density : 1.18 kg/m3

Computational Domain UAV Star-CCM+ OpenFOAM E F A B H J G D C Face ABCD: Inflow Boundary, V = 25 m/s Face ABEF, CGHD, BFGC, AEHD: Farfield Face EFGH: Outflow Boundary, P = 101325 Pa Face J: Velocity = 0 m/s Farfield Velocity = 25 m/s Farfield Pressure = 101325 Pa Farfield Temperature = 300K Farfield Density = 1.18 kg/m3

Mesh Cell Count: Wing NACA 64-210: Star-CCM+: 1.25 million OpenFOAM: 1.2 million UAV: Star-CCM+: 1.9 million :

Results and Discussion Preliminary Computational Assessment on an Aircraft Wing in Star-CCM+. Flow past an aircraft rectangular wing of NACA 64210 with OpenFOAM solver. Computational modeling of the Heavy rainfall over a UAV using both commercial code Star-CCM+ and open-source software OpenFOAM.

Ratio of finest to coarsest mesh Results and Discussion Mesh Convergence Studies – NACA 64-210 Star-CCM+ OpenFOAM     Order of Convergence Grid Convergence Index , Ratio of finest to coarsest mesh

Results and Discussion Comparison of Aerodynamic Characteristics for NACA 64-210 wing in Star-CCM+

Results and Discussion Contours for with rain and without rain case for NACA 64-210 wing in Star-CCM+ Computed Coefficient of Pressure contours Without Rain With Rain

Particle Trajectories Results and Discussion Splashing for NACA 64-210 wing in Star-CCM+ Particle Trajectories

Results and Discussion Comparison of Aerodynamic Characteristics for NACA 64-210 wing using OpenFOAM

Results and Discussion Contours for with rain and without rain case for NACA 64-210 wing in OpenFOAM Computed Wall Film Thickness contours Splashing With Rain

Results and Discussion

Results and Discussion Comparison of Aerodynamic Characteristics for UAV using Star-CCM+

(at 0.1m in spanwise direction) Results and Discussion Comparison of Contours for with rain and without rain case for UAV using Star-CCM+ Without Rain With Rain Computed Contours(4 AoA) Velocity (at mid plane) Velocity (at 0.1m in spanwise direction) Vorticity

(at 0.1m in spanwise direction) Results and Discussion Comparison of Contours for with rain and without rain case for UAV using OpenFOAM Without Rain With Rain Computed Contours(4 AoA) Velocity (at mid plane) Velocity (at 0.1m in spanwise direction) Vorticity

Results and Discussion Comparison of Aerodynamic Characteristics for Star-CCM+ and OpenFOAM

Results and Discussion Contours of wall film thickness on surface of a UAV Star-CCM+ OpenFOAM

Results and Discussion

Results and Discussion

Conclusion and Future Work Present computational study has show a potential for using open source software OpenFOAM for high fidelity study for complex computational problems The results computed using OpenFOAM have shown expected aerodynamic behavior which is in general agreement with available experimental data as well as match closely to the data computed from the commercial software Star-CCM+ Results predicts higher percentage of performance degradation at lower AoA which matches with earlier data The current work have been resulted in a dedicated solver to solve rainfall problem in OpenFOAM

Conclusion and Future Work Novel impingement, wall film and separation module which can work with one equation SA turbulent model will help in predicting early stall as shown by experimental data obtained at NASA. Experiments will be carried out in future to verify the computational data and making more robust models to predict the performance more accurately. A flight dynamics coupling to define the unsteady aerodynamic characteristics of a propeller powered UAV will be carried out as part of Future Work

Thank You Questions !!!

Backup Slide -1

Backup Slide - 2 Pre-processing (Mesh Generation): snappyHexMesh ( OpenFOAM inbuilt mesher ) Gmsh ( 3D Unstructured mesher) Solver : OpenFOAM Post-Processing: Paraview

Backup Slide - 3