Transition Flow and Aeroacoustic Analysis of NACA0018 Satish Kumar B, Fred Mendonç a, Ghuiyeon Kim, Hogeon Kim

Transcription

1 Transition Flow and Aeroacoustic Analysis of NACA0018 Satish Kumar B, Fred Mendonç a, Ghuiyeon Kim, Hogeon Kim

2 Transition Flow and Aeroacoustic Analysis of NACA0018 Satish Kumar B, Fred Mendonç a, Ghuiyeon Kim, Hogeon Kim

3 Transition Flow and Aeroacoustic Analysis of NACA0018 Satish Kumar B, Fred Mendonç a, Ghuiyeon Kim, Hogeon Kim

4 Contents Introduction Geometry & Computational Domain Meshing Details Boundary Conditions Steady State Analysis Preliminary Study Unsteady LES Acoustic & Spectral Analysis Comparison with Experiments References

5 Introduction Whistling noise from the side mirror at high speed is an ongoing serious issue for both design and aero-acoustic performance of a vehicle. Design changes in the side mirror for reducing its contribution to the total drag of vehicle and also to improve the fuel economy potentially cause a discrete noise by flow transition from Laminar to Turbulent via the growth of Tollmein - Schlichting (T-S) instability waves. Simple case of flow over NACA0018 aerofoil at Re=1.6e5 is considered to analyze the complex features of flow transition and its associated noise at fundamental level.

6 Aerofoil and Computational Domain Aerofoil: NACA0018 Aerofoil Angle of Attack (AOA): 6 Degrees Aerofoil Chord Length(CL):0.08 m Aerofoil Span:0.16 m (2CL) Free stream Diameter: 2 m (25CL) Trailing Edge Thickness:8e-5 m (0.002CL)

7 Mesh Modeling Mesh Models Surface Remesher Trimmer Prism Layer Mesher Reference Values: Prism Layer Stretching: 1.1 Base Size: 4 mm Maximum cell size: 1600 % Number of prism layers: 15 Prism layer thickness: 1 mm Surface size: Relative min. size: 0.5 mm Relative target size: 64 mm Template Growth Rate: Default growth rate: Slow Boundary growth rate: Medium

8 Mesh Volumetric Controls 2 mm

9 Mesh Volume Number of cells: 11 Million Y+ approximately 1 on complete airfoil surface Prism Layers: 15 Prism Layer Thickness: 1 mm Prism Layer Stretching: 1.1 Predominantly Hexahedral in the free stream domain

10 Steady State Physics Preliminary analysis Physics Models: Air Three Dimensional Steady State Ideal Gas Segregated Flow Solver Segregated Energy Solver K-Omega SST Turbulence All Y + wall Treatment Reference Values: Reference Pressure: Pa Initial Conditions: Static Pressure:0.0 Pa (Gauge) Static Temperature:300 k Turbulent Intensity:0.01 Turbulent Viscosity Ratio:10 Velocity:[30,0,0] m/s

11 Boundary Conditions Boundary Conditions: Free Stream Mach Number: Static Temperature: 300 K Pressure: 0 Pa Turbulence Intensity: 0.01 Turbulent Viscosity Ratio: 10 Free Stream Non Reflecting B.C Advantageous than Reflecting B.C such as Velocity Inlet Pressure Inlet or Outlet

12 Steady State Mesh Frequency Cut Off Measure of mesh ability in terms of resolution to capture the turbulent flow structures in the frequency of interest. Demonstrates ability of mesh to predict well beyond 1kHz in the boundary layer Defined in terms of Isotropic Fluctuating component of Velocity and the Cell Dimension in direction of interest. f MC 2 k / 3 ( Hz ) 2D

13 Steady State Scalar Contours (Z=0.08 m) Turbulent Viscosity Ratio Velocity Magnitude

14 Steady State Pressure Coefficients

15 Unsteady LES Physics Physics Models: Air Three Dimensional Implicit Unsteady Ideal Gas Segregated Flow Solver Segregated Energy Solver LES Turbulence 1 Time Step[s]= 10*Maximum Frequency Resolution [Hz] Highest Frequency to be resolved: 10,000 Hz Time Step: 1e-5 s WALE (Wall Adapting Local Eddy) Sub grid Scale All Y + wall Treatment Aero acoustics Ffwocs Williams-Hawkings Reference Values: Reference Pressure: Pa Initial Conditions: Started from Steady RANS Calculation

16 Unsteady Pressure Coefficients : Instantaneous No instabilities indicate laminar flow on pressure side and leading edge suction side Pressure side : Breakdown to turbulence Suction side: Breakdown to turbulence Indicates suction-side inception and growth of T-S instabilities

17 Pressure Coefficients: Unsteady Mean Vs Steady

18 Scalar Contours: Wall Shear Stress (suction side)

19 Scalar Contours: Suction Side Q-Criterion (3D Vorticity) Velocity contours on Iso-surface of Q= +10

20 Computed Instantaneous vorticity field at TE

21 Acoustic Analysis Free- space Green s function based FW-H solver used in STAR- CCM+ environment for the computation of sound propagation. Aerofoil surface is considered as the impermeable dipolar source. Receiver location is chosen as the same point considered in previous computations and experiments to compare and validate the SPL at tonal frequency. The acoustic pressure signal build at the receiver location is generated from the integration of signals from the all the source elements of aerofoil surface.

22 Fast Fourier Transform of Radiated Pressure at FW-H Receiver ( L: STAR-CCM+, R: CFD Reference)

23 Spectral Analysis Point Spectra: Point located above Suction side near the trailing edge at approx. 0.8*chord Shows peak at 2358 Hz Surface Spectra: Pressure and Suction sides Shows localized excitations at various selected frequencies Symmetry Plane Spectra Shows localized excitations at various selected frequencies Shows localized and near-field radiation (directivity) patterns

24 Suction Side Pressure Spectra 2358 Hz 1000Hz 1500Hz 2000Hz 2358 Hz 2500Hz 3000Hz

25 Pressure Side Pressure Spectra 2358 Hz 1000Hz 1500Hz 2000Hz 2358 Hz 2500Hz 3000Hz

26 Symmetry Plane Pressure Spectra & Near-field radiation 8mm 4mm 2358 Hz 2mm 1mm 1000Hz 1500Hz 2000Hz 2358 Hz 2500Hz 3000Hz

27 Direct Propagation 2000Hz 2500Hz

28 Comparison with Experimental Data

29 Highlights of Experimental Work Author/Journal,Year Flow Measurement Flow Visualization Aero-acoustics /Noise T. Nakano et al. /JWE,2007 PIV Liquid Crystal Coating Condenser Microphone ( Bottom wall of AWT Y. Takagi et al. / JSV,2006 PIV Liquid Crystal Coating Condenser Microphone ( wall of AWT Fujisawa et al. /TVSJ,2002 PIV Smoke Sound Level Meter 10 mm underneath of Top wall of AWT

30 Spectrum of Aerodynamic Noise CFD Vs Expt.

31 Turbulent Stress (u rms / U o ) CFD Vs PIV (Nakano et al.) PIV STAR-CCM+ Kim & Lee

32 Turbulent Stress (v rms / U o ) CFD Vs PIV (Nakano et al.) PIV STAR-CCM+ Kim & Lee

33 Turbulent Stress (u v / U o2 ) CFD Vs PIV (Nakano et al.) PIV STAR-CCM+ Kim & Lee

34 References H-J Kim, S. Lee, N. Fujisawa., Computation of unsteady flow and aerodynamic noise of NACA0018 airfoil using large-eddy simulation. International Journal of Heat and Fluid Flow 27, pp T. Nakano, N. Fujisawa, Y. Oguma, Y. Takagi, S. Lee., Experimental study on flow and noise Characteristics of NACA0018 airfoil. Journal of Wind Engineering and Industrial Aerodynamics 95, pp Y. Takagi, N. Fujisawa, T. Nakano, A.Nashimoto., Cylinder wake influence on the tonal noise and Aerodynamic characteristics of a NACA0018 airfoil. Journal of Sound and Vibration 297, pp Tomimatsu S, Fujisawa N., Measurement of Aerodynamic Noise and Unsteady Flow Field around a Symmetric Airfoil. Journal of Visualization Vol.5, No.4,pp

35 References Mendonca, F., Read, A., Caro, S., Debatin, K. and Caruelle, B Aeroacoustic Simulation of Double Diaphragm Orifices in an Aircraft Climate Cooling System. AIAA STAR-CCM+ Version User Guide and Methodology Manuals, CDadapco, London, UK, 2011.

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