Preliminary Experimental Assessment Of The Performance Of Tube-Axial Fans Designed With Different Vortex Criteria (original) (raw)

Abstract

Rotor-only axial fans feature rotors designed according to different vortex criteria. Nowadays the literature does not exhaustively clarify when a specific swirl distribution has to be used and which are the advantages/drawbacks in terms of fan performance and efficiency. A review of the experimental performance of rotor-only axial fans designed with different vortex criteria is summarized here in Φ − Ψ and σ − δ (specific speed-specific diameter) graphs to identify the best operating conditions of each design. Four rotor-only axial fans (two free-vortex, a constant-swirl and a rigid-body swirl one) are tested on an ISO-5801-A rig. For two of them, flow velocities at rotor exit are measured with a 5-hole probe. The result is an experimentally based map around the Cordier curve for rotor-only axial fans. Indications on the best Φ − Ψ range for fans designed using different vortex criteria are provided and explained. The effects of increasing the tip clearance on the rotor performance at design duty are investigated as well.

Figures (7)

Figure 1: Schematic representation of the blade shapes deriving from the application of different spanwise gradients of circulation; adapted from Cory (2010). Vil iiisit MUU LUT Up LAUY LULUITS AS WHil WerSs> VAU, \2ull)). In this heterogeneous panorama few indications are given on the suitable operational condi- tions of NFV rotors. Vad (2010) reports that NFV designs are suitable for fans of small diameter, low blade count, and low rotor speed that operate at high flow-rate and/or total pressure rise. Bamberger (2015) gives quantitative support to this statement presenting o — 0 (specific speed and diameter) charts obtained with CFD-trained meta-models on optimized geometries: NFV geometries are suitable for operational conditions that lie below the well-known Cordier curve (i.e., at relatively low o — 6 combinations). However, the highest total-to-static efficiencies for rotor-only fans are obtained with free-vortex designs lying on the Cordier line. Nonetheless, nowadays a clear experimentally-based picture of the duty points of rotor-only fans designed according to different vortex criteria is still not available (e.g., Pascu (2009)).

Figure 1: Schematic representation of the blade shapes deriving from the application of different spanwise gradients of circulation; adapted from Cory (2010). Vil iiisit MUU LUT Up LAUY LULUITS AS WHil WerSs> VAU, \2ull)). In this heterogeneous panorama few indications are given on the suitable operational condi- tions of NFV rotors. Vad (2010) reports that NFV designs are suitable for fans of small diameter, low blade count, and low rotor speed that operate at high flow-rate and/or total pressure rise. Bamberger (2015) gives quantitative support to this statement presenting o — 0 (specific speed and diameter) charts obtained with CFD-trained meta-models on optimized geometries: NFV geometries are suitable for operational conditions that lie below the well-known Cordier curve (i.e., at relatively low o — 6 combinations). However, the highest total-to-static efficiencies for rotor-only fans are obtained with free-vortex designs lying on the Cordier line. Nonetheless, nowadays a clear experimentally-based picture of the duty points of rotor-only fans designed according to different vortex criteria is still not available (e.g., Pascu (2009)).

Figure 2: Performance of rotor-only fans at DP or BEP for different vortex criteria: FV (A), AV (CO), ForV (©); a) flow coefficient versus fan total pressure coefficient (® — V -7p) chart, b) specific speed versus specific diameter (co — 6) chart. Note that only high-efficiency fans were reported in Fig. b). Cross markers (x) indicate the fans tested within this work.

Figure 2: Performance of rotor-only fans at DP or BEP for different vortex criteria: FV (A), AV (CO), ForV (©); a) flow coefficient versus fan total pressure coefficient (® — V -7p) chart, b) specific speed versus specific diameter (co — 6) chart. Note that only high-efficiency fans were reported in Fig. b). Cross markers (x) indicate the fans tested within this work.

Table 2: Geometrical parameters of the fan blades tested. Angles and chord lenght rounded t integer values.* Values computed with local velocities on cylindrical surfaces. Table 2: Geometrical parameters of the fan blades tested. Angles and chord lenght rounded to

Table 2: Geometrical parameters of the fan blades tested. Angles and chord lenght rounded t integer values.* Values computed with local velocities on cylindrical surfaces. Table 2: Geometrical parameters of the fan blades tested. Angles and chord lenght rounded to

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