Investigation of airflow in empty chambers with perforated diffuser designed for air handling units in terms of flow and acoustic

Outlet cross-sectional area of fans used in air handling units (AHUs) is smaller than cross-sectional area of chambers which are located next to the fan of HVAC equipment such as heating/cooling coils, silencer (sound attenuator), filter or heat recovery elements. In order to operating of air handling units (AHUs) in terms of energy efficiency, it is required that air blown by the fan diffuses from small cross-sectional area to large cross-section area as short as possible distance. To provide the diffusion, perforated diffuser are used after the fan cell. In addition to these diffusers diffuse the air as uniformly as and with minimal pressure loss, aerodynamically generated noise caused by perforated diffusers is also important. In this study, airflow characteristic and noise induced airflow were investigated in chamber with truncated pyramid perforated diffuser. The effects of geometrical design parameters of truncated pyramid perforated diffusers on pressure loss, airflow diffusion performance of diffuser and sound pressure level in the chamber were found out. As geometrical design parameters, porosity, thickness, draft angle, distance of diffuser, hole geometry type, hole hydrualic diameter, hole array type and diffuser surface type were determined. An experimental setup for flow analysis was established. Experimental studies were carried out for two different perforated diffusers, the mesh structure and turbulence model of the numerical model are validated. The effects of geometrical design parameters on pressure loss, velocity distribution and aeroacoustic performance were investigated numerically. Solid models were created in SolidWorks. Flow and aeroacoustic analyzes were performed in ANSYS Fluent package program. Incompressible, steady state flow conditions are supposed for numerical flow analyzes. In the numerical solutions, standard k-ε turbulence model was used. In the numerical aeroacoustic analyzes, transient flow condition were carried out in the ANSYS-Fluent program and the module of the Ffowcs Williams and Hawkings (FW-H) method build in the program was used. The time-dependent signals from the microphones in three different locations placed in a perforated diffuser cell were converted to a frequency range of 0-1000 Hz by Fast Fourier Transform (FFT) method and sound pressure level (SPL) values were obtained.