Efficiency gain of low-speed axial flow rotors due to forward sweep

A combined acoustic-aerodynamic diagnostics methodology is presented herein, involving the phased array microphone technique and an in-house rotating source identifier processing algorithm. The methodology makes possible the industrial onsite investigation of unducted or short-ducted rotor-only axial fans. Its application is illustrated in a case study of a free-inlet, free-exhausting fan, surveyed from the upstream direction. A methodology is outlined for guaranteeing the appropriateness of averaging of the phased array microphone records. A technique is proposed for eliminating the ambiguity of the angular position of the rotor noise sources. A complete set of noise source maps of various frequencies have been evaluated. Noise sources, such as tip leakage flow and suction side blade boundary layer flow, have been identified. Empirical correlations have been pointed out between indicators of aerodynamic noise and aerodynamic loss along the blade span. Such correlations may contribute to redesign guidelines for simultaneous reduction of noise and improvement of efficiency at prescribed fan performance.

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“…Preliminary studies to this paper have been published in Benedek and Vad. [16][17][18] Fan of case study, diagnostics methodology…”

Section: Introductionmentioning

confidence: 99%

An industrial onsite methodology for combined acoustic-aerodynamic diagnostics of axial fans, involving the phased array microphone technique

Benedek

Vad

2016

International Journal of Aeroacoustics

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“…In the automotive industry, the leakage phenomenon strongly impacts the global performance of the cooling fan. [19][20][21] Thus, due to confinement constraints, the leakage gap is larger than in other areas: the gap-to-blade height is about 2%. 22 This paper deals specifically with the phenomenon of leakage flow in an axial automotive cooling fan.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of an actively controlled automotive cooling fan using steady air injection in the leakage gap

Azzam

Paridaens

Ravelet

et al. 2017

Proceedings of the Institution of Mechanical Engineers, Part A:

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International audiencen an axial fan, a leakage flow driven by a pressure gradient between the pressure side and the suction side occurs in the gap between the shroud and the casing. This leakage flow is in the opposite direction to the main flow and is responsible for significant energy dissipation. Therefore, many authors have worked to understand this phenomenon in order to reduce these inherent energy losses. Up to now, most of the studies reported in the literature have been passive solutions. In this paper, an experimental controlling strategy is suggested to reduce the leakage flow rate. To this end, a fan with hollow blades and a specific drive system were designed and built for air injection. Air is injected in the leakage gap at the fan periphery. The experiment was performed for three rotation speeds, five injection rates and two configurations: 16 and 32 injection holes on the fan's circumference. The experimental results of this investigation are presented in this articl

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“…4 The application of forward sweep (FSW) demonstrated to be beneficial in reducing these rotor losses. 5 In particular, Vad et al 5 used a statistical method to analyse rotor data from the literature and showed that CDV bladings can achieve an efficiency increase of 2 %-3 % thanks to the introduction of FSW in blade design. In particular, blades with higher circulation gradients potentially achieve higher efficiency gains.…”

Section: Introductionmentioning

confidence: 99%

“…5. Thus, fan total pressure coefficient É is obtained from equation (1) after substitution of equations (4) to (5), and used in equation 7to improve the guess value of x* that was assigned at step 1.…”

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confidence: 99%

Forward sweep to improve the efficiency of rotor-only tube-axial fans with controlled vortex design blades

Masi

Castegnaro

Lazzaretto

2016

Proceedings of the Institution of Mechanical Engineers, Part A:

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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. KEYWORDS Rotor-only axial fans, Vortex criteria, Axial-fan design, Arbitrary vortex, Non-Free Vortex, Cordier curve NOMENCLATURE const generic constant c chord length [mm] c tip tip chord length [mm] r radius [m] R tip radius [m] tc tip clearance [mm] D fan diameter [m] b c airfoil camber [%] T aerodynamic rotor torque [Nm] q v flow-rate [m 3 /s] c u local swirl velocity [m/s] c a2 local axial velocity [m/s] c a = qv π D 2 4 ·(1−ν 2) mean axial velocity [m/s] v m = qv π D 2 4 velocity at fan exit [m/s] n rotational speed [rpm] Re tip = ρ·(πnD 60)·c tip µ Reynolds number DF Lieblein Diffusion Factor FVP = 1 2 ρv 2 m fan velocity pressure [Pa] ∆p t−s fan total-to-static pressure rise [Pa] OPEN ACCESS Downloaded from www.euroturbo.eu 1 Copyright c ⃝ by the Authors FTP=∆p t−s +FVP fan total pressure [Pa] ν hub-to-tip ratio ω angular velocity [rad/s] Φ = qv (π D 2 4)(πnD 60) flow-rate coefficient Ψ = (F T P or ∆p t−s) 1 2 ρ(πnD 60) 2 pressure coefficient η = (F T P or ∆p t−s)·qv T ·ω efficiency σ = n·q 0.5 v F T P 0.75 specific-speed δ = D·F T P 0.25 q 0.5 v specific-diameter ρ air mass density [kg/m 3 ] ξ stagger angle (with respect to fan axis) [ • ] µ air dynamic viscosity [Pa s] Γ circulation [m 2 /s] Σ a = c a2 ca dimensionless axial velocity ϵ s = cu ca dimensionless tangential velocity INTRODUCTION In this paper the performance of 30 rotor-only axial fan designed according to different vor-tex criteria is analyzed with the aim of providing fan designers with indications on the suitable choice of swirl distribution for a given duty. The rotor-only configuration is largely the most common for low-to-medium pressure-rise axial-fan applications. In this layout fixed vanes and diffuser are absent and the only aerodynamic components are the impeller and the external casing. The resulting simplicity corresponds to cheapness of purchase and maintenance but it is paid with the loss of the dynamic pressures associated with the axial and tangential velocities at rotor exit (except the small amounts con...

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Efficiency gain of low-speed axial flow rotors due to forward sweep

Cited by 9 publications

References 17 publications

An industrial onsite methodology for combined acoustic-aerodynamic diagnostics of axial fans, involving the phased array microphone technique

An industrial onsite methodology for combined acoustic-aerodynamic diagnostics of axial fans, involving the phased array microphone technique

Experimental investigation of an actively controlled automotive cooling fan using steady air injection in the leakage gap

Forward sweep to improve the efficiency of rotor-only tube-axial fans with controlled vortex design blades

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