Experiments and Numerical Predictions of Flow Rates and Aero-Acoustics from Small Radial Notebook Blowers

B1 - Computational Aeroacoustics

The performance of a notebook system depends upon the thermal cooling capacity of the blower/heat exchanger combination, which in turn is dictated by the effective airflow rate produced by the blower. The cooling capacity increases with increased airflow, but so does the acoustic noise. However, ergonomic limits of the acoustic noise from notebooks need to be adhered to, which causes most notebook blowers to operate below maximum rotational speeds. This leads to a scenario in which the performance of many notebook systems is acoustically limited. It is therefore of great importance to optimize notebook blower designs for maximum flow rate and low acoustic noise. This optimization has historically been performed by building expensive prototypes and performing experimental investigations. It is beneficial to numerically optimize the blower designs to reduce design time and prototype cost, and this requires accurate numerical techniques. It is only recently that numerical characterization of airflow and acoustic performance has received increased attention due to the availability of advanced simulation techniques in commercial software. The accuracy of these techniques to predict noise generated by small radial blowers need to be determined. In this paper, numerical simulations of a typical radial notebook blower are performed to first determine accuracy of the airflow and pressure performance of the blower when compared to experimental data. The flow field simulations are performed using unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. Thereafter, aero-acoustic simulations are undertaken. Two different blower setups are investigated: one setup where the blower is in free field and the other one where the blower is mounted in a bracket. The bracket is generally used in experimental evaluation of notebook blowers. The Ffowcs-Williams and Hawkings (FWH) analogy is used in the aero-acoustic predictions. Good agreement is demonstrated for airflow and pressure performance between measurements and numerical predictions. The acoustic experiments show good repeatability for the blade-pass-frequency (BPF), while large variability is observed for the second harmonic. The noise level at the BPF is the highest peak value and the predictions show promise, but accurate aero-acoustic predictions are still challenging.