Establishment of a Beamforming Dataset on Basic Models of Low-Speed Axial Fan Blade Sections

Abstract

Introduction and objectivesLow-speed axial flow fans are widely used in human environment. Some examples are as follows: fans in heating, ventilating and air conditioning (HVAC) for residential buildings as well as for non-residential buildings with occasional human access, and fans of industrial air technology (e.g. air supply, ventilation, cooling) operating in the vicinity of human personnel. In order to moderate the environmental impact of emitted fan noise on humans, and to ensure a proper aerodynamic operation as well, a concerted aeroacoustic and aerodynamic investigation and improvement of low-speed axial fans is a timely issue in the turbomachinery community.In order to correspond to the simultaneous user demands of limitation in space and in rotor speed -being a basis for noise reduction as well -, the elemental blade sections of the aforementioned fans are often characterized by moderate Reynolds numbers, even below the critical value of 1.5·105 [1]. For achieving the prescribed aerodynamic performance -flow rate, total pressure rise -even at moderate diameter, rotor speed, and rotor blade count, such fans are often of high design specific performance, i.e. the blade sections are designed for high load (high lift). This corresponds to pronounced streamwise adverse pressure gradient on the blade suction side downstream of the suction peak. Such adverse effect is amplified due to the fact that the fan frequently operates in a throttled state relative to the design point, i.e. the flow incidence to the blade sections is increased. The resultant thickening or even separation of the suction side boundary layer tends to increase the turbulentboundary-layer-trailing edge noise and the separation-stall noise [1][2]. The aeroacoustic investigation of highly loaded / high incidence blade sections is therefore a topic of great practical importance, with special regard to discovering the correlation between the streamwise evolution of the boundary layer thickness and the spatial distribution of the noise sources associated with the thickened / separated boundary layer. In [3][4][5], a correlation has been found between the loss generated in the suction side boundary layer -represented by the momentum thickness -and the radiated broadband noise. This implies that by the detailed investigation of the boundary layer, additional

Lift and drag force measurements on basic models of low-speed axial fan blade sections

“…Thus, the present authors' long-term aim is to reduce the acoustic emission along with the aerodynamic losses. The aerodynamic measurements linked to preliminary acoustic studies 7,8 are presented in this paper.…”

Beamforming studies on basic models of low-speed axial fan blade sections

“…At the present state of investigation, the mean flow deviation discussed by Roger and Moreau (2010) has been disregarded (conf. Balla and Vad, 2017). Therefore, α has been defined as the geometrical angle between the chord line and the longitudinal axis of the test section.…”

“…The Mach number is 0.06, and thus, incompressible flow is considered. Further details on the measurement setup and the measurement conditions are given in Balla and Vad (2017).…”

“…Considering the aerodynamic measurement data published by Mueller (1999) on flat and cambered plates, a 2D aerodynamic approach has been judged to be fair at the present level of evaluation (conf. Balla and Vad, 2017).…”

A fuzzy clustering method for periodic data, applied for processing turbomachinery beamforming maps

“…This unit has 24 omnidirectional electret microphones mounted flush against the array surface. They are arranged along logarithmic spiral arms.The diameter of the circumscribed circle is 0.95 m[3]. The array was placed perpendicularly to the fan axis of revolution, while the distance between the array and the fan inlet plane was 1.83 tip diameters.…”