Reduction of fan noise bymeans of (circular) side-resonators; theory and experiment

One of the main noise sources in computers are the cooling fans. An important aspect of the noise they generate is tonal noise produced at the rotational frequency of the fan, the blade passing frequency (BPF), and its higher harmonics. Previous research pointed out that so-called side resonators can be applied successfully to reduce this tonal noise. A variety of side resonator geometries is available. A model describing viscothermal wave propagation in a circular side-resonator and the connected duct and the preliminary results of a parameter study of that model where presented previously. The experimental verification of the model is presented here

Air loads on a rigid plate oscillating normal to a fixed surface

This paper deals with the theoretical and experimental investigation on a rigid, rectangular plate oscillating in the proximity of a fixed surface. The plate is suspended by springs. The airloads generated by the oscillating motion of the plate are determined. Due to the fact that the plate is rigid, the system is modelled as a 1-DOF system. The influence of the surrounding air is detected by changes in the plate's natural frequency and damping. For the behaviour of the air in the gap between the plate and the fixed surface an analytical solution is presented. This solution includes the effects of inertia, viscosity, compressibility and thermal conductivity. It is shown that the main parameters governing the motion of the air in the gap are the shear wave number, the reduced frequency, the narrowness of the gap and the aspect ratio of the plate. With these parameters the validity of several simplifications can easily be demonstrated and solutions, given in the literature, can be put in perspective. Special experiments were carried out with an oscillating solar panel in order to verify the analytical model. The analytical results and the experimental results show fair agreement. The solutions shows that for low shear wave numbers the effects of viscosity cannot be discarded. \u

Viscothermal wave propagation including acousto-elastic interaction, Part II: Applications

In Part I of the present paper a parameter analysis showed that the most efficient model to describe viscothermal wave propagation is the low reduced frequency model. In order to demonstrate the wide range of applicability of the low reduced frequency model, a number of examples from the literature are discussed in Part II. An overview of fundamental solutions and general applications is given. Because the models are all written in terms of dimensionless parameters and solutions for various co-ordinate systems are given, this paper also serves as a solution overview. \u