An approximate hybrid approach for computing low-frequency outdoor sound propagation

• The study conceptualizes and tests a hybrid method for outdoor sound propagation. • A semi-analytical finite element method is coupled to a direct numerical computation. • The method is efficient and accurate for long-range sound propagation. • The approach offers a practical tool for noise prediction in engineering problems. Accurate and fast outdoor sound models are essential for assessing noise from infrastructure like wind turbines, highways, and industrial facilities. This paper presents an approximate hybrid method for solving long-range acoustic problems by coupling a normal-mode approach with the numerical solution of the linearized Euler equations (LEEs). The method computes a discrete mode spectrum using a weak Galerkin method from an aeroacoustic eigenequation that accounts for meteorological profiles, atmospheric absorption, gravity, and impedance ground conditions. A pressure field modal decomposition scheme then maps the mode spectrum to the LEE solution, which incorporates detailed geometry, meteorology, and diverse acoustic sources. The acoustic far field is then efficiently computed through an algebraic operation. We validate the method with long-range propagation problems from the infrasound community and a wind turbine model, showing excellent agreement with direct numerical methods while significantly reducing computational resources. This approach offers a practical tool for noise prediction in applications like wind park and highway noise mapping.