[OCEAN]Acoustic noise prediction of air turbines for wave energy converter

Research Focus

Numerical analysis of operational noise of breakwater-linked wave turbine bypass system

What is 'Wave energy converter'?

Wave energy converters use surface waves to generate power. For example, one type of wave energy converter generates power by using wave motion as a piston to drive air in and out of a chamber, with the moving air driving a turbine.

(Image source : https://sharkresearch.earth.miami.edu/)

Numerical Approach

1. Numerical analysis of operational noise of breakwater-linked wave turbine bypass system
: Proudman Acoustic Power (Steady-state analysis)

2. Prediction of noise level at external acoustic receiving point of turbine-bypass system
: Ffowcs Williams Hawkings Analogy (Unsteady analysis)

CFD Results

1. Pressure
– The maximum pressure occurs at the turbine inlet and has the same value as the bypass valve.
– Lower pressures appear as turbine rotation speed increases at the maximum operating conditions,

2. Velocity
– Under maximum power conditions, the maximum and average velocity were 52.6 m/s and 29.3 m/s, respectively.

CAA(Computational Aero-acoustic Analysis) Results

1. Proudman acoustic power
– Acoustic power of more than 100dB appears under both rated and maximum operating conditions.
– Since the difference in noise level due to changes in conditions is less than 1%, turbine noise is not affected by the presence or absence of the resonance chamber of the bypass valve.

2. Ffowcs Williams Hawkings Analogy
– The noise receiving point is located 170m away from the turbine-bypass system, which is the noise source.

– Since the blade passing frequency(BPF) appears in the 400Hz area, it can be seen that the conditions applied to the noise analysis are theoretically valid.
– Due to the influence of white noise generated from the bypass valve, high sound pressure appears both before and after the turbine blade frequency.
– Since the noise value from CAA does not reflect the background noise occurring at the actual measurement site, noise evaluation considering a certain level of background noise is necessary.
– Domestic noise environment standards were applied as an example to evaluate whether the noise level at the receiving point satisfies the noise standard.