Introduction

Thermal comfort plays a key role in creating pleasant and productive indoor environments. Air flow in a closed room matters. Fans are one of the most critical equipment that is used worldwide in order to attain thermal comfort both at home, workplace and in public areas. Air circulation keeps the indoor temperatures at a comfortable level, enhances the quality of air, and allows the cooling to be energy-efficient [1-2]. Thermal comfort and energy efficiency vary based on a set of design and aerodynamic parameters that determine the effectiveness of a ceiling fan. The major design parameters are the rotational speed, fan diameter, number of blades, geometrical angles of horizontal and vertical inclination of the blades, camber angle, stagger angle, and angles of flow in the inlet and outlet of the blades. Also, blade specific parameters such as forward sweep, root and tip angles of attack, and tip width are important factors that dictate the velocity of the airflow, volumetric flow rate, torque and the overall aerodynamic performance. The overall impact of all these factors is on the convection and evaporation of heat transfer and distribution of air to the surroundings, which improves thermal comfort in the indoor environment. A combination of these parameters is needed to achieve a quiet, efficient cooling that can support occupant comfort, productivity and sustainability objectives. The evaluation of thermal comfort usually takes into account the air speed, humidity, temperature, and speed distribution generated by the fan and it shows that the optimized airflow patterns are one of the factors that enhance the perceived air quality and lessen energy usage than using air conditioning solely. This combined knowledge of fan and blade characteristics is gaining significance with the increase in requirements of residential, commercial and office cooling systems that are comfortable, quiet and sustainable. 

The natural world provides the world with tremendous inspirations to resolve complicated engineering issues. Natural organisms have evolved over billions of years to demonstrate efficiency, adaptability and low power consumption, qualities which are often better than the less efficient technology solutions. The science of biomimicry has resulted in new fields of discovery in materials science to architecture and aerodynamics. An example of this is the almost silent flight of a bird like an owl that has special wing designs. Through research and replication of such characteristics, engineers will be able to come up with fan blades of better design with better airflow and less noise and that is why nature designs are not only elegant but also very amazing in making our lives better and easier. 

Some of the noise mitigation methods are to increase cutoff clearance and cutoff lip radius to smooth off velocity profiles and minimize tonal noise, blade stagger to reduce pressure gradient caused by turbulence (at the cost of efficiency), acoustically line fan casing, reduce annular clearance, and quarter-wavelength acoustic resonator at the fan cutoff. All approaches trade noise reduction performance against such design considerations as size, efficiency, or manufacturability [7]. The paper Lee et al. provides a study that gives both numerical and experimental research to determine the types of trailing edge serrations on ceiling fan blades to mitigate aerodynamic noise. Half-at-tip serrations recorded the highest noise reduction in the tested settings, then there were the rectangular serrations. This is a viable aerodynamic noise control technique experimentally proven by validation with a metal stand fan, that serrations can actually be used to reduce trailing edge noise.