Drasko Masovic Doctoral Forum University of Music and Performing Arts Graz June 16, 2017 Drasko Masovic Sound Radiation from an Open Pipe with a Mean Flow Supervisors: Prof. Dr. R. Höldrich, Prof. Dr. G. Eckel, Dr. A. Fuchs

Contents Case study Main acoustic phenomena Measurement results Estimation of sound radiation analytical approach numerical approach

Case study Geometry Mean flow Sound wave

Geometry Axisymmetric geometry (2D) Pipe Opening straight circular semi-infinite thin rigid wall Opening straight cut sharp edge

Mean flow Jet Surrounding gas gas – dry air low Mach number: M = V/c < 0.3 temperature: 20ºC < T < 300ºC Surrounding gas cold and still air

Sound wave Sound source Sound wave deep inside the pipe low frequency (Helmholtz number: ) example: a = 2cm, c = 343m/s → f < 2.5kHz small amplitude (SPL < 150dB)

Applications Automotive applications exhaust system, tail-pipe pass-by noise excitation of vehicle’s body air-conditioning outlets Musical applications wind instruments sound field in rooms spatial sound synthesis

Main flow/acoustic phenomena incident sound wave diffraction at the edge refraction in the mixing region directivity diffraction refraction

Analytical approaches Levine and Schwinger (1948) no mean flow low frequencies

Analytical approaches Munt (1977) (hot) mean flow full frequency range + accurate for low frequencies and cold flows – mathematically involved, few physical interpretations – oversimplified mean flow (→ inaccurate refraction)

Laboratory measurements M = 0.3, T = 20°C, ka = 0.18, 0.36... Atvars et al. (1965) T = 20°C, ka = 0.53, M = 0, 0.1, 0.3… M = 0.2, ka = 0.53, T = 38°C, 149°C, 260°C

Experimental setup flow equipment acoustic equipment

Experimental setup Blower Elektroror SD 900 max. volume flow 14.5m3/min power 11kW

Experimental setup Heaters total power 110kW

Experimental setup Loudspeaker DAP audio AB-12 freq. range 55-2500Hz RMS power 300W

Experimental setup Microphones NTi Audio M2230 equivalent noise level 16 dB(A) accuracy ±1dB @ 20-4000Hz

Measured: the directivity patterns Experimental setup Excitation signal – swept-sine Sound acquisition – 18 microphones Mean flow: M = 0, 0.05, ... 0.25 T = 40°C, 100°C, 200°C, 300°C Measured: the directivity patterns

No-flow (reference) case Comparison with Levine & Schwinger (1948) f [Hz] ka σ Lmin [dB] Lmax [dB] 281 0.1 0.20 -0.60 0.24 1407 0.5 0.30 -0.54 0.63 2533 0.9 0.47 -0.79 1.18

Very low frequencies (negligible refraction) M = 0...0.25 T = 40°C ka = 0.1 M = 0.1 T = 40...300°C ka = 0.1 ·· measured – Munt (1977) ·· measured – Munt (1977)

Increasing frequency M = 0.25 T = 300°C ka = 0.1...0.9 ·· measured – Munt (1977)

Simple model incident sound – plane wave inside the pipe diffraction – vortex-sound interaction at the edge (low M and low ka values) refraction in the mixing region diffraction refraction

Estimation of the directivity diffraction refraction

Estimation of the directivity diffraction refraction

Numerical calculations Fluid Dynamics Acoustics M = 0.25

Numerical calculations Computational Fluid Dynamics Reynolds-averaged Navier-Stokes equations (RANS) Computational Acoustics Method 1: Linearized Euler Equations (LEE) Method 2: Convected Wave Equation (CWE) M = 0.25

Computational acoustics M = 0.25, T = 300ºC, ka= 0.3 Method 1 (LEE) + accurate (includes vortices) – unstable – high computational costs Method 2 (CWE) + efficient and robust – inaccurate (no vortices)

Computational acoustics Method 2 + “vortex effect” + implicit vortex at the edge + efficient and robust – limited to low M and low ka values M = 0.15, T = 41ºC, ka= 0.5

Summary Systematic measurements of the directivity effects of the mean flow (velocity and temperature) and frequency low Mach number, low frequency Simple physical model insight into the key physical phenomena reasonable accuracy simple geometries and flows

Summary Numerical calculations comparison of different acoustic equations and numerical techniques Method 2 + “vortex effect” improved accuracy compared to Method 2 lower computational costs and more robustness compared to Method 1 range of validity?

Publications Planned: D. Masovic, F. Zotter, E. Nijman, J. Rejlek, and R. Höldrich, “Directivity measurements of low frequency sound field radiated from an open cylindrical pipe with a hot mean flow,” 9th ISNVH Congress, Graz, SAE Technical Paper 2016-01- 1822, 2016 D. Masovic, “Comments on convective amplification of sound sources in flows,”, ASRO Journal of Applied Mechanics, vol. 1, no. 1, pp. 20-23, 2016. D. Masovic, E. Nijman, J. Rejlek, and R. Höldrich, “A simple model of the far-field directivity of an open circular pipe with a hot flow,” in Proceedings of DAGA 2017, Kiel, pp. 1222-1225, 2017. D. Masovic, E. Nijman, J. Rejlek, and R. Höldrich, “Towards a boundary condition for convective wave equation and sound diffraction at a trailing edge inside a flow,” in Proceedings of DAGA 2017, Kiel, pp. 1301-1304, 2017. Planned: D. Masovic, E. Nijman, J. Rejlek, and R. Höldrich, “'Comparison of different approaches for calculation of sound radiation from an open pipe with a flow”, ICTCA 2017, Vienna, July/August 2017

THANK YOU FOR YOUR ATTENTION! Drasko Masovic Doctoral Forum University of Music and Performing Arts Graz June 16, 2017 THANK YOU FOR YOUR ATTENTION! Drasko Masovic