Arthropods, including pollinators and pests, have high positive and negative impacts on human well-being and the economy, and there is an increasing need to monitor their activity and population growth. The monitoring of arthropod species is a time-consuming and financially demanding process. Automatic detection can be a solution to this problem. Here, we describe the setup and operation mechanism of an infrared opto-electronic sensor-ring, which can be used for both small and large arthropods. The sensor-ring consists of 16 infrared (IR) photodiodes along a semicircle in front of an infrared LED. Using 3D printing, we constructed two types of sensor-ring: one with a wider sensing field for detection of large arthropods (flying, crawling, surface-living) in the size range of 2–35 mm; and another one with a narrower sensing field for soil microarthropods in the size range of 0.1–2 mm. We examined the detection accuracy and reliability of the two types of sensor-ring in the laboratory by using particles, and dead and living arthropods at two different sensitivity levels. For the wider sensor-ring, the 95% detectability level was reached with grain particles of 0.9 mm size. This result allowed us to detect all of the macroarthropods that were applied in the tests and that might be encountered in pest management. In the case of living microarthropods with different colors and shapes, when we used the narrower sensor-ring, we achieved the 95% detectability level at 1.1 mm, 0.9 mm, and 0.5 mm in the cases of F. candida, H. nitidus, and H. aculeifer, respectively. The unique potential of arthropod-detecting sensors lies in their real-time measurement system; the data are automatically forwarded to the server, and the end-user receives pest abundance data daily or even immediately. This technological innovation will allow us to make pest management more effective.
This paper extends existing semi-empirical models on the frequency prediction of vortex shedding. Moderate Reynolds numbers are investigated being of interest in low-speed axial fan design. By an extensive literature review, a new parametrization is proposed for the factor establishing a connection between boundary layer properties and vortex shedding characteristics. Measurement data on symmetrical and non-symmetrical NACA profiles, and on flat and cambered plates, are processed. It is found that the value of the factor is influenced by the relative thickness of the profiles and by the angle of attack. Based on the measurement results, an empirical value is given for the vortex spacing ratio for flow past airfoils. With the use of the proposed empirical model, the vortex shedding frequency of various airfoil profiles and operating conditions can be predicted.
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
This paper presents comparative data on the aerodynamic lift and drag of basic model representations of low-speed axial fan blade sections. Three main types of blades are investigated: flat plate, cambered plate and RAF6-E profiled airfoil. Lift and drag force are measured at three different Reynolds numbers (0.6•10 5 , 10 5 and 1.4•10 5) around the threshold value of 10 5. The measurement data is compared to literature data. The aerodynamic force measurements reveal that, for Reynolds numbers below 10 5 , cambered plate blade sections can be superior to airfoil profiles in terms of aerodynamic efficiency, especially in the high-load range. The effect of leading edge bluntness is also investigated. Leaving the leading edge of cambered plates blunt, tends to be uncritical for low Reynolds numbers at angles of attack between 4°and 10° but is critical at angles between 0° and 4°. KEYWORDS airfoil, cambered plate blade, low-Reynolds-number axial fan, low-speed fan NOMENCLATURE A area [mm 2 ] c chord [mm] CL lift coefficient CD drag coefficient d maximum height of the camber line [mm]
The paper reports on establishing a beamforming dataset, relying on the phased array microphone (PAM) technique, on the broadband noise of rectilinear basic models of low-speed axial fan blade sections. A cambered plate profile is in the focus of the studies, in comparison with a flat plate and a traditional airfoil profile. At low Reynolds numbers, cambered plate blade sections have a potential to perform aerodynamically better than profiled airfoil sections. Thus, the established dataset aims at contributing to the design background of aerodynamically efficient, low-noise, low-Reynolds-number fans. The wind tunnel-PAM configuration enables the acoustic investigation over the plane being normal to the spanwise direction at midspan. An illustrative study on representative cases selected out of the dataset demonstrates the capabilities and limitations of the presently available experimental and evaluation method. Spatially simultaneously resolved information is presented on the signatures of systematically investigated classes of blade section noise. KEYWORDS beamforming, blade noise, cambered plate blade, low-speed axial fan, phased array microphone Abbreviations BG background LE leading edge PAM phased array microphone TE trailing edge 1. INTRODUCTION AND OBJECTIVES Axial flow fans characterized by blade sections of chord Reynolds numbers of Re £ 10 5 are termed herein as "low-Reynolds-number fans". Such fans are of relatively small size and/or rotor speed, e.g. cooling fans for computers (Huang, 2003) and for electric motors (Borges, 2012), or refrigerator fans (Gue et al., 2011). Axial fans are often required to provide a prescribed flow rate and/or total pressure rise even at moderate diameter and/or rotor speed. These requirements are in accordance with the constraints of limited available space and/or speed-the latter being constrained e.g. by a directly-driving electric motor-in industrial applications. For these fans, the flow coefficient and the total pressure coefficient may extend over F » 0.4 and Y » 0.6, incorporating operational ranges throttled significantly below the design flow rate (e.g. Corsini and Rispoli, 2004). Such fans are termed herein as "high-specific-performance fans". Their blade sections are often of high aerodynamic load-i.e. high lift coefficient-, high camber, and are often exposed to high a angles of attack. Cambered plate blades of circular arc camber line are often applied in axial fans, enabling a relatively simple and low-cost manufacturing technique. A further reason for choosing cambered plate blades appears in low-Reynolds-number fan applications. For Re £ 10 5 , a cambered plate section may perform aerodynamically better than a profiled airfoil section. The potential benefits are the following: higher maximum lift coefficient CL, and higher maximum lift-to-drag ratio CL/CD. Illustrative examples are given for such favourable trends by Carolus (2003), referring to Albring (1978). A comprehensive explanation is given herein on the basis of the experimental data and discussi...
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