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

Abstract

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]

An empirical model to determine lift and drag coefficients of cambered plates at moderate Reynolds numbers

“…As already reported in Balla and Vad, 15 the endwall effect may have a significant impact on measurements in closed test section wind tunnels. Mueller 14 also found that the endwall effect may be notable for cambered plates at low Re values.…”

“…Based on this the filtering method established herein focuses on the Re = 60,000 points, which are most likely to be corrupted by the endwall effect. The filtering was applied to those results which were not corrected to infinite span previously, namely the Mueller 14 and own 15 cases (see Table 1). Two types of fit have been made, first the trendlines have been fitted to the data including the Re = 60,000 point.…”

“…The measurement setup and the uncertainty calculations are described in more detail in Balla and Vad. 15 A flat plate and a cambered plate with 8% relative camber were under investigation at three Reynolds numbers: 60,000, 100,000, and 140,000. The aspect ratio of the plates was 1.5.…”

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Figure 2.Measurement setup. 15 1: motor, 2: frequency converter, 3: radial fan, 4: inlet bell mouth, 5: guide vanes, 6: flexible connector, 7: split diffuser, 8: honeycomb, 9: turbulence reduction screens, 10: transition element, 11: closed test section.

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A semi-empirical model for predicting the frequency of profile vortex shedding relevant to low-speed axial fan blade sections

“…The extension of existing models is necessary for resolving the trends in measurements on various airfoils and flow conditions. Studies on isolated airfoils are relevant for low solidity fan applications, as discussed in Balla and Vad (2019). In the future, the authors wish to apply the results for the vortex shedding prediction of blade profiles used in the design of low-speed axial fans.…”