Internal Sound Pressure Level Estimation Considering Design Through Computational Aeroacoustics

Abstract

Subsea chokes differ from the standard choke designs that can be found in for example the IEC 60534-8-3 standard, due to their geometry but also due to the environment. Contrary to topside chokes where monitoring for sound and vibration can be carried out in a relatively straightforward manner, noise and vibration monitoring is not easily executed subsea, which means that the estimate of the generated noise needs to be calculated, or extrapolated in some way from lab data. Computational methods to validate designs often provide an alternative method to physical validation testing when size or recreating particular environments are impractical. However, to be able to use computational analysis for this purpose, it is essential to ensure that a sound and benchmarked methodology is applied. This paper discusses an optimized methodology that combines Computational Aeroacoustics and IEC 60534-8-3 for the estimation of the internal sound pressure level (SPL) generated by choke valves. Three broad types of tools (all broadband models) are available to estimate hydrodynamic induced SPL, namely: 1) one-way coupled Computational Fluid Dynamics (CFD), 2) acoustic solvers, 3) two-way coupled CFD and acoustic solvers, also called Computational Aeroacoustics (CAA) solvers. Out of these three types, CAA accounts for both the geometry of the equipment generating the internal SPL, but also models the complex interaction between hydrodynamics and acoustics, including tones generated by cavities. While the advantage in terms of output is significant, CAA comes at a large computational cost due to the requirements in space and time discretization that must be satisfied to properly resolve the frequency range from 12.5 Hz to 20 kHz. The CAA methodology presented in this paper is validated against two sets of data obtained in laboratory conditions for Mach numbers ranging from 0.08 to 0.36. Then the same methodology is applied to the specific design of the choke valve. The obtained outputs in form of an acoustical efficiency and peak frequency are then used to tune the IEC 60534-8-3 method, this allows accurate estimation of internal SPL for the given geometry. The combination of the CAA and IEC enables efficient consideration of the actual geometry of the choke with regards to internal SPL prediction against a wider range of conditions without requiring a larger set CAA calculations. The methodology presented in this paper can be applied to similar problems ensuring faster and more accurate results compared to the other available industry practices like physical testing.