An Analysis of the Loss Mechanisms in Low-Speed Axial Fans Using Scaling Arguments and Their Effects on a Proposed New Definition of Efficiency

2006 ◽  
Author(s):  
Douglas R. Neal
Keyword(s):  
Energy Equation ◽  
Pressure Rise ◽  
Axial Fan ◽  
Low Speed ◽  
Static Efficiency ◽  
Axial Fans ◽  
Integral Energy ◽  
Definition Of ◽  
Scaling Arguments ◽  
Ventilation Fan

Low-speed axial fans are used extensively for ventilation purposes in industrial and commercial buildings. In agricultural applications, such as a greenhouse, the ventilation is critical, since entire crops can be damaged or destroyed if a clean air supply is not maintained. The cost-marginal nature of these businesses demand that operating costs be kept to a minimum, hence there is a strong motivation to develop higher efficiency ventilation fans. An analysis of a low-speed axial fan has been developed using a control volume-based energy balance. The specific fan is an axial ventilation fan that is commonly found on agricultural facilities such as green-houses or livestock buildings. These fans induce an airflow from a large building into the open atmosphere at very low (or often effectively zero) system restriction or pressure rise. The definition for static efficiency, which is commonly used by the axial fan community, is examined and its implications are discussed. Since static efficiency yields a zero-percent efficient fan at a zero pressure rise operating condition, the ventilation fan industry has developed an alternate definition of efficiency. This alternate definition of efficiency, along with other proposed definitions, are described and their limitations are discussed. A new definition of efficiency is introduced and its basis in the integral energy equation is identified. The primary loss mechanisms of low-speed axial turbomachinery are discussed and scaling arguments are developed and used in the integral energy equation analysis. The results of this analysis yield an expanded expression of efficiency in which the loss mechanism terms can be empirically determined. When analyzed with values for a particular fan system, these results can further be used as the basis for an optimization study of that fan system.

Computational Modeling of Low-Pressure Fan Flows

2000 ◽  
Author(s):  
Siddharth Thakur ◽  
Wanlai Lin ◽  
Jeffrey Wright ◽  
Wei Shyy ◽  
Ron Lievens
Keyword(s):  
Pressure Rise ◽  
Low Pressure ◽  
Flow Fields ◽  
Numerical Dissipation ◽  
Computational Tool ◽  
Axial Fan ◽  
Static Efficiency ◽  
Blade Shape ◽  
Axial Fans ◽  
Mass Flow Rates

A CFD-based computational tool is used to analyze flows in axial fans. Computed results for an axial fan flow field for one particular blade shape are presented; certain global quantities such as the mass-averaged pressure rise and the static efficiency available from test data for different mass flow rates are used to evaluate the trends predicted by the CFD results. The characteristic feature of the fan flow fields presented here is a very low pressure rise; due care is exercised to ensure that grid dependence and numerical dissipation do not smear out the key features of the computed flow fields.

Blade Sweep for Low-Speed Axial Fans

1989 ◽  
Author(s):  
Terry Wright ◽  
William E. Simmons
Keyword(s):  
Volume Flow Rate ◽  
Pressure Rise ◽  
Design Procedure ◽  
Acoustic Properties ◽  
Excess Noise ◽  
Axial Fan ◽  
Low Speed ◽  
Axial Fans ◽  
Computer Codes ◽  
Selection Of

The available literature on aerodynamic and acoustic properties of axial fans with swept blades is presented and discussed with particular emphasis on noise mechanisms and the influence of high-intensity inlet turbulence on “excess” noise. The acoustic theory of Kerschen and Envia for swept cascades is applied to the problem of axial fan design. These results are compared to available data and a provisional model for specifying sweep angles is presented. The aerodynamic performance theory for swept-bladed rotors of Smith and Yeh is adapted for use in designing low speed axial fans. Three prototype fans were designed using the resultant computer codes. One is a baseline fan with blade stacking lines radially oriented, and two are fans having swept blades of increasingly greater forward sweep. Aerodynamic testing shows that performance of the fans lie within a band width of about ± two percent of volume flow rate and pressure rise predictions in the region of design performance, effectively validating the design procedure for selection of the blading parameters. Noise testing of the fans was carried out and the results show an average noise reduction for the swept-bladed fans of about 7 dBA overall, and a reduction of pure tone noise at blade-pass frequency of about 10 dB compared to the zero-sweep baseline model in close agreement with the theory of Kerschen and Envia.

Blade Sweep for Low-Speed Axial Fans

1990 ◽  
Vol 112 (1) ◽  
pp. 151-158 ◽  
Author(s):  
T. Wright ◽  
W. E. Simmons
Keyword(s):  
Volume Flow Rate ◽  
Pressure Rise ◽  
Design Procedure ◽  
Acoustic Properties ◽  
Excess Noise ◽  
Axial Fan ◽  
Low Speed ◽  
Axial Fans ◽  
Computer Codes ◽  
Selection Of

The available literature on aerodynamic and acoustic properties of axial fans with swept blades is presented and discussed with particular emphasis on noise mechanisms and the influence of high-intensity inlet turbulence on “excess” noise. The acoustic theory of Kerschen and Envia for swept cascades is applied to the problem of axial fan design. These results are compared to available data and a provisional model for specifying sweep angles is presented. The aerodynamic performance theory for swept-bladed rotors of Smith and Yeh is adapted for use in designing low-speed axial fans. Three prototype fans were designed using the resultant computer codes. One is a baseline fan with blade stocking lines radially oriented, and two are fans having swept blades of increasingly greater forward sweep. Aerodynamic testing shows that performance of the fans lies within a band width of about ± 2 percent of volume flow rate and pressure rise predictions in the region of design performance, effectively validating the design procedure for selection of the blading parameters. Noise testing of the fans was carried out and the results show an average noise reduction for the swept-bladed fans of about 7 dBA overall, and a reduction of pure tone noise at blade-pass frequency of about 10 dB compared to the zero-sweep baseline model, in close agreement with the theory of Kerschen and Envia.

scholarly journals Introduction of an Universal Scale-Up Method for the Efficiency of Axial and Centrifugal Fans

2014 ◽  
Author(s):  
Peter F. Pelz ◽  
Stefan S. Stonjek
Keyword(s):  
Test Data ◽  
Scale Up ◽  
Pressure Rise ◽  
Flow Coefficient ◽  
Total Efficiency ◽  
Scaling Method ◽  
Centrifugal Fans ◽  
Axial Fans ◽  
Definition Of ◽  
Acceptance Tests

Acceptance tests on large fans to prove the performance (efficiency and total pressure rise) to the customer are expensive and sometimes even impossible to perform. Hence there is a need for the manufacturer to reliably predict the performance of fans from measurements on down-scaled test fans. The commonly used scale-up formulas give satisfactorily results only near the design point, where inertia losses are small in comparison to frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulas used so far fail. In 2013 Pelz and Stonjek introduced a new scaling method which fullfills the demands ( [1], [2]). This method considers the influence of surface roughness and geometric variations on the performance. It consists basically of two steps: Initially, the efficiency is scaled. Efficiency scaling is derived analytically from the definition of the total efficiency. With the total derivative it can be shown that the change of friction coefficient is inversely proportional to the change of efficiency of a fan. The second step is shifting the performance characteristic to a higher value of flow coefficient. It is the task of this work to improve the scaling method which was previously introduced by Pelz and Stonjek by treating the rotor/impeller and volute/stator separately. The validation of the improved scale-up method is performed with test data from two axial fans with a diameter of 1000 mm/250mm and three centrifugal fans with 2240mm/896mm/224mm diameter. The predicted performance characteristics show a good agreement to test data.

Development of Autonomous Design Technique for Axial Fans Using Numerical Optimization

2005 ◽  
Author(s):  
Taku Iwase ◽  
Kazuyuki Sugimura ◽  
Taro Tanno
Keyword(s):  
Numerical Optimization ◽  
Simulated Annealing Algorithm ◽  
Static Pressure ◽  
Pressure Rise ◽  
Navier Stokes ◽  
Axial Fan ◽  
Automatic Program ◽  
Axial Fans ◽  
Computational Fluid Dynamics Cfd ◽  
Annealing Algorithm

We designed an axial fan for servers using computational fluid dynamics (CFD) and numerical optimization. The performance of the fan, namely static pressure rise and efficiency, was calculated using commercial CFD software based on an incompressible Reynolds-averaged Navier-Stokes (RANS) solver. An automatic program developed in-house was used to generate the grids for CFD calculation. Numerical optimization—using a simulated annealing algorithm (SA)—was used for determining the optimized shape of the fan. After optimizing the fan, initial and optimized fan designs were made for experiments using rapid prototyping, and their performances, based on such things as efficiency and noise level, were measured. Results demonstrated that the optimized fan design achieved higher efficiency than the initial design. Multi optimization was also developed for maximizing the fan efficiency and minimizing the casing height. An additional finding was that there was a trade-off between the fan efficiency and casing height.

scholarly journals Experiment-Based Preliminary Design Guidelines for Consideration of Profile Vortex Shedding From Low-Speed Axial Fan Blades

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Gábor Daku ◽  
János Vad
Keyword(s):  
Vortex Shedding ◽  
Design Guidelines ◽  
Preliminary Design ◽  
Axial Fan ◽  
Noise Emission ◽  
Blade Vibration ◽  
Low Speed ◽  
Blunt Trailing Edge ◽  
Axial Fans ◽  
Semi Empirical

Abstract This paper presents hot-wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for the consideration of profile VS in preliminary design of axial fans in the moderation of VS-induced blade vibration and noise emission.

Aerodynamic Characteristics and Noise Analysis of a Low-Speed Axial Fan

2018 ◽  
Author(s):  
Bo Luo ◽  
Wuli Chu ◽  
Wei Dong ◽  
Xiangyi Chen
Keyword(s):  
Noise Analysis ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Low Noise ◽  
Axial Fan ◽  
Tonal Noise ◽  
Low Speed ◽  
Optimum Choice ◽  
Aerodynamic Performances ◽  
Axial Fans

Axial fans are widely used in modern industry and new regulations and stringent environmental concerns are prompting manufacturer to design efficient low-noise axial fans. This paper is focused on improving the aerodynamic performances and reducing the tonal noise at BPF and its harmonics by the optimum choice of lean-swept blade and the stacking line for the low-speed axial fan. The aerodynamic characteristics of the axial fan with a shroud are explored by CFD with ANASYS CFX. A hybrid method, SST turbulence model for flow and FW-H equation for acoustics, is chosen to predict the radiated noise. The accuracy and reliability of predicted aerodynamic and aeroacoustics results are verified by comparing both computation and experimental data. A number of modified blades with different leaned angle, swept angle and the stacking lines are modeled and analyzed, and the investigation into the optimum choice of lean-swept blade and the stacking line is conducted according to aerodynamic performances and tonal noise. Q-criterion which can visualize the major flow disturbances is applied for the purpose of identification of acoustic sources. The turbulent flow structures on the leading edge, tip and suction side of the blade are main noise sources. An optimal modification is determined through the analysis of the aerodynamic performances and noise, which is to achieve the desired performances by blade sweep and lean and adjusting the stacking line. The results show that aerodynamic and acoustic performances of the optimized fan are better than that of the original fan and the improvement is more obvious to change the stacking line with centre of gravity compare to blade sweep and lean for the low-speed axial fan.

Combined Aerodynamic and Phased Array Microphone Studies on Basic Models of Low-Speed Axial Fan Blade Sections

2018 ◽  
Author(s):  
Esztella Balla ◽  
János Vad
Keyword(s):  
Reynolds Number ◽  
Phased Array ◽  
High Efficiency ◽  
Low Reynolds Number ◽  
Low Noise ◽  
Axial Fan ◽  
Noise Sources ◽  
Low Speed ◽  
Axial Fans ◽  
Low Reynolds

The paper presents comparative aerodynamic and aeroacoustic studies on basic models of blade sections of low-speed, low-Reynolds-number axial fans. The wind tunnel experiments incorporated representative cambered plate and airfoil blade profiles. The aerodynamic measurements revealed that, for low Reynolds numbers, cambered plate blade sections may perform aerodynamically better than airfoil sections. A phased array microphone system, combined with a dipole beamforming and spatial filtering technique, offered a potential for localizing the noise sources in both streamwise and transversal direction. The acoustic studies focused on the profile vortex shedding noise. The results were qualitatively evaluated and compared with the semi-empirical noise prediction model developed by Brooks, Pope, and Marcolini. The measurements are considered as preparation of a dataset contributing to the background for designing high-efficiency, low-noise axial fans operating at low Reynolds number.

Aeroacoustic Analysis of Low-Speed Axial Fans With Different Rotational Speeds in the Design Point

2017 ◽  
Author(s):  
Patrick Buchwald ◽  
Damian M. Vogt ◽  
Julien Grilliat ◽  
Wolfgang Laufer ◽  
Michael B. Schmitz ◽  
...  
Keyword(s):  
Flow Separation ◽  
Rotational Speed ◽  
Numerical Study ◽  
Pressure Rise ◽  
Far Field ◽  
Noise Sources ◽  
Blade Loading ◽  
Design Point ◽  
Low Speed ◽  
Axial Fans

One of the main design decisions in the development of low-speed axial fans is the right choice of the blade loading versus rotational speed, since a target pressure rise could either be achieved with a slow spinning fan and high blade loading or a fast spinning fan with less flow turning in the blade passages. Both the blade loading and the fan speed have an influence on the fan performance and the fan acoustics and there is a need to find the optimum choice in order to maximize efficiency while minimizing noise emissions. The present paper addresses this problem by investigating five different fans with the same pressure rise but different rotational speeds in the design point. In the first part of the numerical study, the fan design is described and steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are conducted in order to identify the performance of the fans in the design point and in off-design conditions. The investigations show the existence of an optimum in rotational speed regarding fan efficiency and identify a flow separation on the hub causing a deflection of the outflow in radial direction as the main loss source for slow spinning fans with high blade loadings. Subsequently, Large Eddy Simulations (LES) along with the acoustic analogy of Ffowcs Williams and Hawkings (FW-H) are performed in the design point to identify the main noise sources and to determine the far-field acoustics. The identification of the noise sources within the fans in the near-field is performed with the help of the power spectral density of the pressure. In the far-field, the sound power level is computed using different parts of the fan surface as FW-H sources. Both methods show the same trends regarding noise emissions and allow for a localization of the noise sources. The flow separation on the hub is one of the main noise sources along with the tip vortex with an increase in its strength towards lower rotational speeds and higher loading. Furthermore, a horseshoe vortex detaching from the rotor leading edge and impinging on the pressure side as well as the turbulent boundary layer on the suction side represent significant noise sources. In the present investigation, the maximum in efficiency coincides with the minimum in noise emissions.

Experimental Investigation of the Effect of Reynolds Number on the Efficiency of Single-Stage Axial Fans

2018 ◽  
Author(s):  
Massimo Masi ◽  
Stefano Castegnaro ◽  
Andrea Lazzaretto
Keyword(s):  
Reynolds Number ◽  
Axial Flow ◽  
Operating Conditions ◽  
Single Stage ◽  
Axial Fan ◽  
Low Speed ◽  
Surface Finishes ◽  
Axial Fans ◽  
The Many ◽  
Testing Standards

Uncertainties surrounding the influence of Reynolds number on the performance of air handling turbomachines are as old as the study of turbomachinery fluid dynamics. In particular, all low-speed turbomachines and most axial-flow fans feature Reynolds numbers that are often lower than the critical value, above which the literature states a limited dependency of blades cascade aerodynamics on Reynolds number. Testing standards already account for this well-known issue, which arises mainly in the case of geometrically similar fans of different size and/or operating conditions. On the other hand, one of the main practical issues in the design of low-speed machines is the disagreement among the most authoritative sources on the value of the critical Reynolds number for axial fans. The many definitions of Reynolds number, which are suited to either fan design purposes or fan performance assessment, introduce additional problems, as the corresponding values may differ by orders of magnitude depending on the chosen definition. A less debated issue deals with the effect of Reynolds number on global performance and efficiency parameters for different axial-flow fan configurations. This paper reports pressure and efficiency data measured at several rotational speeds of four axial fans that feature different configurations, hub-to-tip ratios, sizes and surface finishes. In particular, the tests consider two 315mm and one 630mm tube-axial fans, and one 800mm vane-axial fan with preswirler blading. Data on two vane-axial fans with straightener, and one preswirler-rotor-stator stage, available in the literature, widen the discussion on the Reynolds number effect on the entire category of single-stage axial fans.

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