RESUMO
When one swings a short corrugated pipe segment around one's head, it produces a musically interesting whistling sound. As a musical toy it is called a "Hummer" and as a musical instrument, the "Voice of the Dragon." The fluid dynamics aspects of the instrument are addressed, corresponding to the sound generation mechanism. Velocity profile measurements reveal that the turbulent velocity profile developed in a corrugated pipe differs notably from the one of a smooth pipe. This velocity profile appears to have a crucial effect both on the non-dimensional whistling frequency (Strouhal number) and on the amplitude of the pressure fluctuations. Using a numerical model based on incompressible flow simulations and vortex sound theory, excellent predictions of the whistling Strouhal numbers are achieved. The model does not provide an accurate prediction of the amplitude. In the second part of the paper the sound radiation from a Hummer is discussed. The acoustic measurements obtained in a semi-anechoic chamber are compared with a theoretical radiation model. Globally the instrument behaves as a rotating (Leslie) horn. The effects of Doppler shift, wall reflections, bending of the tube, non-constant rotational speed on the observed frequency, and amplitude are discussed.
RESUMO
OBJECTIVES: To investigate, first, the effects of septal deviation and concha bullosa on nasal airflow, and second, the aerodynamic changes induced by septoplasty and partial lateral turbinectomy, using computational fluid dynamics (CFD). METHODS: A three-dimensional model of a nasal cavity was generated using paranasal sinus computed tomography images of a cadaver with concha bullosa and septal deviation. Virtual septoplasty and partial lateral turbinectomy were performed on this model to generate a second model representing the postoperative anatomy. Aerodynamics of the nasal cavity in the presence of concha bullosa and septal deviation as well as postoperative changes due to the virtual surgery were analyzed by performing CFD simulations on both models. Inspiratory airflow with a constant flow rate of 500 mL/second was used throughout the analyses. RESULTS: In the preoperative model, the airflow mostly pass through a narrow area close to the base of the nasal cavity. Following the virtual operation, a general drop in the maximum intranasal air speed is observed with a significant increase of the airflow through right middle meatus. While in the preoperative model the greatest reduction in pressure is found to be in the localization of anterior septal deviation on the right side and confined to a very short segment, for the postoperative model, it is observed to be in the nasal valve region in both nasal cavities. Following septoplasty and partial lateral turbinectomy, total nasal resistance is reduced significantly. CONCLUSIONS: CFD simulations promise to make great contributions to understand the airflow characteristics of healthy and pathologic noses. Before surgery, planning for any specific intervention using CFD techniques on the nasal cavity model of the patient may help foreseeing the aerodynamic effects of the operation and might increase the success rate of the surgical treatment.
