Axial fan tip clearance noise: Experiments, Lattice–Boltzmann simulation, and mitigation measures

The effect of tip clearance in an axial fan on its aerodynamic and aeroacoustic performance is investigated experimentally as well as via a Lattice–Boltzmann flow simulation method. An increase in tip clearance degrades fan pressure rise and efficiency, but also increases significantly the overall sound power emitted by the fan. A large tip clearance causes a clear structure of well distinguishable unsteady vortices which interact with neighboring blades and hence produce an increase in broadband sound. Moreover, if, compared to the design flow rate, there is a moderate flow rate reduction, the local tip vortex systems of all individual blade tips form a circumferentially coherent flow structure, resulting in distinct humps of sound pressure in the acoustic far field. By means of a rigid ring-type protrusion fixed to the inner casing wall, the generation of the tip clearance vortices and slowly rotating coherent flow structures could be suppressed. As a consequence, the sound emitted by the fan is substantially reduced.

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Influence of Blade Sweep on the Energetic Behavior of Axial Flow Turbomachinery Rotors at Design Flow Rate

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-53544 ◽

2004 ◽

Cited By ~ 2

Author(s):

Ja´nos Vad ◽

Ali R. A. Kwedikha ◽

Helmut Jaberg

Keyword(s):

Aspect Ratio ◽

Flow Rate ◽

Axial Flow ◽

Pressure Rise ◽

Design Flow ◽

Tip Clearance ◽

Total Efficiency ◽

Low Aspect Ratio ◽

Axial Velocity Profile ◽

Bladed Rotor

Experimental and computational studies were carried out in order to survey the energetic aspects of forward and backward sweep in axial flow rotors of low aspect ratio blading for incompressible flow. It has been pointed out that negative sweep tends to increase the lift, the flow rate and the ideal total pressure rise in the vicinity of the endwalls. Just the opposite tendency was experienced for positive sweep. The local losses were found to develop according to combined effects of sweep near the endwalls, endwall and tip clearance losses, and profile drag influenced by re-arrangement of the axial velocity profile. The forward-swept bladed rotor showed reduced total efficiency compared to the unswept and swept-back bladed rotors. This behavior has been explained on the basis of analysis of flow details. It has been found that the swept bladings of low aspect ratio tend to retain the performance of the unswept datum rotor even in absence of sweep correction.

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Effect of Two- and Three-Dimensionally Designed Guide Vanes with Different Camber Length on Static Pressure Recovery of a Wall-Mounted Axial Fan

Processes ◽

10.3390/pr9091595 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1595

Author(s):

Yong-In Kim ◽

Yong-Uk Choi ◽

Cherl-Young Jeong ◽

Kyoung-Yong Lee ◽

Young-Seok Choi

Keyword(s):

Flow Rate ◽

Guide Vane ◽

Dynamic Pressure ◽

Pressure Rise ◽

Design Flow ◽

Low Flow ◽

Axial Fan ◽

Flow Angle ◽

Numerical Effort ◽

Vane Angle

This study was based on a numerical effort to use the motor support (prop) as a guide vane when the motor of a wall-mounted axial fan was located at the fan outlet while maintaining the structural and spatial advantage. The design for the guide vane followed two- and three-dimensional methods. The inlet vane angle, meridional length (total), and meridional length with a vane angle of zero (0) degrees (linear) were considered as design variables. At the design and some low flow rate points, the 2D design offered the most favorable performance when the meridional length with a vane angle of zero (0) degrees (linear) was 30% based on total length, and was the worst for 70%. The 3D design method applied in this study did not outperform the 2D design. In the 2D design concept, averaging the flow angle for the entire span at the design flow rate could ensure a better pressure rise over a more comprehensive flow rate range than weighting the flow angle for a specific span. In addition, the numerical results were validated through an experimental test, with an important discussion of the swirl (dynamic pressure) component. The influence of the inlet motor and turbulence model are presented as a previous confirmation.

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Velocity characteristics in a multiphase pump under different tip clearances

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650920946533 ◽

2020 ◽

pp. 095765092094653

Author(s):

Guangtai Shi ◽

Zongku Liu ◽

Yexiang Xiao ◽

Helin Li ◽

Xiaobing Liu

Keyword(s):

Velocity Distribution ◽

Flow Rate ◽

High Speed ◽

Stokes Equations ◽

Design Flow ◽

Tip Clearance ◽

High Speed Photography ◽

Hydraulic Loss ◽

Impeller Blade ◽

Multiphase Pump

To investigate the effect of tip clearance on the velocity distribution in a multiphase pump, the internal flow and velocity distribution characteristics in pump under different tip clearances are studied using experimental and numerical methods. Simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS) and the standard k-ε turbulence model are carried out using ANSYS CFX. Under conditions of inlet gas void fraction (IGVF) is 5% at the flow rate of 0.6Q, 0.7Q and 0.8Q (Q is the design flow rate), the accuracy of the numerical method is verified by comparing with the experimental data using high-speed photography. Results show that the leakage flow interacts with the main flow and evolves into the tip leakage vortex (TLV). Due to the TLV, the pressure, velocity, turbulent kinetic energy (TKE), vorticity and streamlines on the S2 stream surface in the impeller and diffuser are changed greatly under different tip clearances. The velocities at the impeller outlet and diffuser inlet along the radial direction are also changed. The axial velocity distribution is similar to the meridional velocity distribution at the impeller blade outlet. While the relative velocity and absolute velocity distribution show the opposite trends. In addition, the vorticity is larger near the tip separated vortex and the hydraulic loss in pump is also increased due to the TLV.

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Effect of Axial Sweep and Tip Extension on Performance of an Axial Fan

Volume 1: Advances in Aerospace Technology ◽

10.1115/imece2016-65967 ◽

2016 ◽

Author(s):

Ankit Bhai Patel ◽

K. Viswanath ◽

Dhyanjyoti Deb Nath

Keyword(s):

Performance Improvement ◽

Flow Direction ◽

Pressure Rise ◽

Aerodynamic Performance ◽

Secondary Flows ◽

Tip Vortex ◽

Low Flow ◽

Pressure Probe ◽

Axial Fan ◽

Stall Margin

Performance enhancement in terms of stall margin increment, increased pressure rise coefficient and increased efficiency is of great need for low speed axial fans. Stacking line modifications in terms of sweep, skew, dihedral or combination of these, as well as blade tip geometry modifications are assumed to be one of the ways to achieve finite performance improvement. Non radial stacking of blade profiles modifies secondary flows, tip vortex effects, hub passage vortex and thus affects aerodynamic performance parameters such as stall margin, efficiency, pressure rise, blade loading. In literature many studies have confined to comparison of few cases which led to conflicting results as modification of stacking line may have different effects in different cases. In the present work, comparison of performance of axial fan rotor with three different blade configurations BSL (baseline), SWP (swept blade) and EXTN (swept blade with extended tip) are considered. The BSL configuration is designed on basis of non-free vortex design. The SWP configuration is obtained by shifting radial stacking line of the BSL in axial flow direction by 10° (Forward sweep). The EXTN configuration is obtained by extending tip profile on pressure surface as well as suction surface by 3% locally. Experiments have been conducted on these three configurations to study effects of these modifications on aerodynamic performance. The flow field has been surveyed using Kiel probe, Three hole pressure probe at many flow rates starting from fully open to fully closed. Unsteady flow analysis at exit of rotors of all configurations is carried out using fast response pressure probe. Experimental results show slight performance improvement in terms of increased stall margin, efficiency, as well as total pressure rise for SWP rotor as well as EXTN rotor compared to BSL rotor at low flow coefficients.

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Compressible Simulation of Flow and Sound Around a Small Axial-Flow Fan With Flow Through Casing Slits

Journal of Fluids Engineering ◽

10.1115/1.4047807 ◽

2020 ◽

Vol 142 (10) ◽

Author(s):

Hiroshi Yokoyama ◽

Katsutake Minowa ◽

Kohei Orito ◽

Masahito Nishikawara ◽

Hideki Yanada

Keyword(s):

Flow Field ◽

Flow Rate ◽

Aerodynamic Performance ◽

Design Flow ◽

Low Flow ◽

Axial Fan ◽

Flow Rates ◽

Blade Tip ◽

Flow Through ◽

Design Flow Rate

Abstract Small axial fans are used for cooling electronic equipment and are often installed in a casing with various slits. Direct aeroacoustic simulations and experiments were performed with different casing opening ratios to clarify the effects of the flow through the casing slits on the flow field and acoustic radiation around a small axial fan. Both the predicted and measured results show that aerodynamic performance deteriorates at and near the design flow rate and is higher at low flow rates by completely closing the casing slits compared with the fan in the casing with slits. The predicted flow field shows that the vortical structures in the tip vortices are spread by the suppression of flow through the slits at the design flow rate, leading to the intensification of turbulence in the blade wake. Moreover, the pressure fluctuations on the blade surface are intensified, which increases the aerodynamic sound pressure level. The suppression of the outflow of pressurized air through the downstream part of the slits enhances the aerodynamic performance at low flow rates. Also, the predicted surface streamline at the design flow rate shows that air flows along the blade tip for the fan with slits, whereas the flow toward the blade tip appears for the fan without slits. As a result, the pressure distributions on the blade and the torque exerted on the fan blade are affected by the opening ratio of slits.

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Axial Fan Performance With Blade-Base Clearance

1983 Joint Power Generation Conference: GT Papers ◽

10.1115/83-jpgc-gt-6 ◽

1983 ◽

Author(s):

T. Wright

Keyword(s):

Flow Rate ◽

Pressure Rise ◽

Axial Fan ◽

Fan Performance

A study to evaluate the influence of increasing the clearance between blade and hub on a controllable pitch axial fan (CPAF) is presented. Fan performance was measured over a range of increasing clearance for several settings of blade pitch angles. The resulting variations of pressure rise, flow rate and efficiency have been correlated as functions of established clearance parameters with good results. The study shows that large base clearances may result in reductions in efficiency and flow rate of 5 percent or greater in a typical CPAF configuration.

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Design of High Efficiency Blowers for Future Aerosol Applications

Volume 2: Fora ◽

10.1115/fedsm2009-78234 ◽

2009 ◽

Author(s):

Raman Chadha ◽

Gerald L. Morrison ◽

Andrew R. McFarland

Keyword(s):

Flow Rate ◽

High Efficiency ◽

Static Pressure ◽

Pressure Rise ◽

Electrical Energy ◽

Design Flow ◽

Preliminary Design ◽

Aerosol Sampling ◽

Wall Functions ◽

Low Efficiency

High efficiency air blowers to meet future portable aerosol sampling applications were designed, fabricated, and their performance evaluated. A preliminary blower design based on specific speed was selected, modeled in CFD, and the flow field simulated. This preliminary blower size was scaled in planar and axial directions, at different rpm values, to set the Best Efficiency Point (BEP) at a flow rate of 100 L/min (1.67×10−3 m3/s @ room conditions) and a pressure rise of 1000 Pa (4″ WC). Characteristic curves for static pressure rise versus air flow rate through the impeller were generated. Experimentally measured motor/blower combination efficiency (ηEXP) for the preliminary design was around 10%. The low value was attributed to the low efficiency of the D.C. motor used (Chadha, 2005). CFD simulations using the κ–ε turbulent model and standard wall function (non-equilibrium wall functions) approach overpredicted the head values. Enhanced wall treatment under-predicted the head rise but provided better agreement with experimental results. The static pressure rise across the final blower is 1021 Pa at the design flow rate of 100 L/min. Efficiency value based on measured static pressure rise value and the electrical energy input to the motor (ηEXP) is 26.5%, a 160% improvement over the preliminary design.

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Axial Fan Performance With Blade-Base Clearance

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239655 ◽

1984 ◽

Vol 106 (4) ◽

pp. 901-905

Author(s):

T. Wright

Keyword(s):

Flow Rate ◽

Pressure Rise ◽

Axial Fan ◽

Fan Performance

A study to evaluate the influence of increasing the clearance between blade and hub on a controllable pitch axial fan (CPAF) is presented. Fan performance was measured over a range of increasing clearance for several settings of blade pitch angles. The resulting variations of pressure rise, flow rate, and efficiency have been correlated as functions of established clearance parameters with good results. The study shows that large base clearances may result in reductions in efficiency and flow rate of 5 percent or greater in a typical CPAF configuration.

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Experimental and Unsteady Numerical Investigation of the Tip Clearance Noise of an Axial Fan

ASME 2013 Turbine Blade Tip Symposium ◽

10.1115/tbts2013-2034 ◽

2013 ◽

Cited By ~ 10

Author(s):

Tao Zhu ◽

Thomas H. Carolus

Keyword(s):

Surface Pressure ◽

Temporal Structure ◽

Pressure Fluctuations ◽

Tip Clearance ◽

Tip Vortex ◽

Far Field ◽

Axial Fan ◽

Clearance Ratio ◽

Wall Pressure Fluctuations ◽

Unsteady Surface Pressure

The aerodynamic and aeroacoustic performance of axial fans are strongly affected by the unavoidable tip clearance. Two identical fan impellers but with different tip clearance ratio were investigated. Unsteady wall pressure fluctuations in the tip region of the rotating blades and on the interior wall of the duct type shroud and the overall sound radiated were analysed by an unsteady numerical Scale-Adaptive Simulation (SAS) and unsteady surface pressure measurements in both, the stationary and rotating system. Based on SAS-predicted pressure fluctuations on the blade surfaces the acoustic analogy according to Ffowcs Williams and Hawkings (FWH) was employed to calculate the sound pressure in the far field. In general, experimentally and numerically determined unsteady flow were found to be a tendentially good agreement. The spatial and temporal structure of the tip vortex system and the resulting unsteady pressure distribution on the surfaces in the vicinity of the blade tips was revealed in good detail. The vortices’ strength and trajectories as well as the unsteadiness are controlled by the size of the tip clearance and the operating point: As tip clearance is increased blade/vortex interaction becomes more prevalent and with it the unsteady surface pressure and eventually the sound radiated into the far field. The broadband tip clearance noise was acceptably predicted from the simulation results, while the prediction at discrete frequency should still be improved in the further work.

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