scholarly journals Axial Fan Performance under the Influence of a Uniform Ambient Flow Field

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Till Heinemann ◽  
Stefan Becker
Keyword(s):  
Flow Field ◽  
Characteristic Curve ◽  
Cross Flow ◽  
Flow Fields ◽  
Low Flow ◽  
Axial Fan ◽  
Ambient Flow ◽  
Fan Performance ◽  
Air Cooled Condensers ◽  
Axial Fans

In their application to air-cooled condensers, axial fans are often subject to the detrimental influence of ambient flow fields at their inlet or outlet. While effects have been investigated mostly under perpendicular cross-flow conditions on fans operating as part of an array in their target design point, this study aims at examining the integral influence of uniform ambient flow fields on a single axial fan over a wide operating range. For this purpose, a wind tunnel fan test rig has been designed and assessed. Multiple angles between uniform ambient flow field and fan axis are examined in their integral influence on the characteristic curve of two distinct industrial axial fans with varying inlet modifications. Increasingly with the fan flow rate, perpendicular inlet cross-flow was found to always have a detrimental influence on fan performance. The straight bladed fan reacted less sensitively than the forward skewed fan, and the adverse cross-flow influence could be reduced with an inlet guard grille and with short conical shroud extensions. Cross-flow at the fan outlet showed potential static fan pressure increases at low flow rates.

Cross Wind Influence on Noise Emission and Computed Vibrational Noise of an Axial Fan

2015 ◽  
Author(s):  
Till Heinemann ◽  
Sven Münsterjohann ◽  
Florian Zenger ◽  
Stefan Becker
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Laser Scanning ◽  
Sound Pressure ◽  
Cross Flow ◽  
Test Rig ◽  
Axial Fan ◽  
Noise Emission ◽  
Axial Fans ◽  
Operating Points

The total noise emissions of two commercial axial fans were measured in a semi-anechoic fan test rig in comparison. The total sound pressure levels and the respective spectra were found to change with the fans’ operating points. Increasing fan flow rates lowered the total acoustic pressure, with a broadband shift towards higher frequencies, keeping perceived (A-weighted) sound pressure levels approximately constant over a wide range of operating points. In a second step, Laser Scanning Vibrometry measurements of the fan blades’ axial motion were conducted in comparison inside a wind tunnel fan test rig. Rotating blade surface vibration data was used as sole input to a Ffowcs Williams and Hawkings algorithm, to estimate noise emission from vibration. The computed noise from surface vibration was found to be hardly affected by the change of fan flow rate. In the application of an axial fan subject to natural wind or induced cross flow at its inlet, the flow field and possible noise emission of the fan changes. Microphone measurements of the cross flow influence inside a semi-anechoic wind tunnel revealed increasing broadband noise with ambient flow field velocity, and an amplification of the sound at the blade passing frequency harmonics. Similar excitations of the blade passing frequency harmonics under cross flow influence were also found in sound pressure spectra computations based on the Laser Scanning Vibrometry measurement data captured in the wind tunnel fan test rig. Blade vibration is considered to contribute to the low frequency tonal noise emission of axial fans operating under cross flow conditions.

Performance of a Low Speed Axial Fan Under Distortion: An Experimental Investigation

2020 ◽  
Author(s):  
Sumit Tambe ◽  
Ugaitz Bartolomé Oseguera ◽  
Arvind Gangoli Rao
Keyword(s):  
Flow Field ◽  
Symmetry Plane ◽  
Vortex Pair ◽  
Axial Fan ◽  
Low Speed ◽  
Fan Performance ◽  
Fuel Burn ◽  
Flow Phenomena ◽  
Order Of Magnitude ◽  
Distortion Index

Abstract In the pursuit of reducing the fuel burn, future aircraft configurations will feature several types of improved propulsion systems, e.g. embedded engines with boundary layer ingestion, high-bypass ratio engines with short intakes, etc. Depending on the design and phase of flight, the engine fan will encounter inflow distortion of varying strength, and fan performance will be adversely affected. Therefore, investigation of the flow phenomena causing performance losses in fan and distortion interaction is important. This experimental study shows the effect of varying distortion index on four aspects of fan performance: distortion topology, upstream redistribution, performance curve, and flow unsteadiness. A low speed fan is tested under 60° circumferential distortion of varying strength, generated using distortion screens. The flow field in the upstream redistribution region is measured using PIV (planar and stereo). The fan performance is obtained using total pressure measurements. The noise spectra measured by a microphone are used to quantify the unsteadiness in the flow field. The distortion index (DC60) varies linearly with the grid porosity at constant wall thickness and aspect ratio of the grid cells. However, the distortion topology is significantly different as a stream-wise vortex pair appears in distorted flow at higher DC60. The vortices are stronger at higher DC60, but their order of magnitude is much lower than the circulation corresponding to fan itself. The spinner, distortion index and topology significantly affect the upstream redistribution mechanism. The vortex pair redistributes the flow which results in lower asymmetry in the symmetry plane. With increasing distortion, the performance is reduced and the unsteadiness is increased.

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.

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

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.

Calculation of the Time-Averaged Flow in Squirrel-Cage Blowers by Substituting Blades With Equivalent Forces

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Markus Tremmel ◽  
Dale B. Taulbee
Keyword(s):  
Flow Field ◽  
Flow Pattern ◽  
Stokes Equations ◽  
Practical Interest ◽  
Transient Simulation ◽  
Low Flow ◽  
Mean Flow ◽  
Fan Performance ◽  
Squirrel Cage ◽  
The Mean

Radial fans of the squirrel-cage type are used in various industrial applications. The analysis of such fans via computational fluid mechanics can provide the overall fan performance coefficients, as well as give insights into the detailed flow field. However, a transient simulation of a 3D machine using a sliding grid for the rotating blades still requires prohibitively large computational resources, with CPU run times in the order of months. To avoid such long simulation times, a faster method is developed in this paper. Instead of solving the transient Navier–Stokes equations, they are first averaged over one impeller rotation, and then solved for the mean flow since only this flow is of practical interest. Due to the averaging process, the blades disappear as solid boundaries, but additional equation terms arise, which represent the blade forces on the fluid. An innovative closure model for these terms is developed by calculating forces in 2D blade rows with the same blade geometry as the 3D machine for a range of flow parameters. These forces are then applied in the 3D machine, and the resulting 3D time-averaged flow field and performance coefficients are calculated. The 3D flow field showed several characteristic features of squirrel-cage blowers, such as a cross-flow pattern through the fan at low flow coefficients, and a vortexlike flow pattern at the fan outlet. The 3D fan performance coefficients showed an excellent agreement with experimental data. Since the 3D simulation solves for the mean flow, it can be run as a steady-state problem with a comparatively coarse grid in the blade region, reducing CPU times by a factor of about 10 when compared to a transient simulation with a sliding grid. It is hoped that these savings in computational cost will encourage other researchers and industrial companies to adopt the new method presented here.

D12 Flow Fields of Semi-Open Axial Fan at Low Flow Rate Condition

2008 ◽  
Vol 2008 (0) ◽  
pp. 151-152
Author(s):  
Sho KUMAMOTO ◽  
Norimasa SHIOMI ◽  
Yoichi KINOUE ◽  
Kenji KANEKO ◽  
Toshiaki SETOGUCHI
Keyword(s):  
Flow Rate ◽  
Flow Fields ◽  
Low Flow ◽  
Axial Fan ◽  
Rate Condition ◽  
Low Flow Rate

scholarly journals Effect of Inlet Geometry on Fan Performance and Inlet Flow Fields in a Semi-opened Axial Fan

2014 ◽  
Vol 7 (2) ◽  
pp. 60-67 ◽  
Author(s):  
Pin Liu ◽  
Norimasa Shiomi ◽  
Yoichi Kinoue ◽  
Toshiaki Setoguchi ◽  
Ying-Zi Jin
Keyword(s):  
Flow Fields ◽  
Axial Fan ◽  
Inlet Flow ◽  
Fan Performance ◽  
Inlet Geometry

Mass transfer from a particle suspended in fluid with a steady linear ambient velocity distribution

1979 ◽  
Vol 95 (2) ◽  
pp. 369-400 ◽  
Author(s):  
G. K. Batchelor
Keyword(s):  
Flow Field ◽  
Velocity Distribution ◽  
Peclet Number ◽  
Transfer Rate ◽  
Free Particle ◽  
Azimuthal Angle ◽  
Flow Fields ◽  
Péclet Number ◽  
Ambient Flow ◽  
Large Peclet Number

This paper is concerned with the rate of transfer of heat or mass from a force-free couple-free particle immersed in fluid whose velocity far from the particle is steady and varies linearly with position. Asymptotic results for both small and large Péclet numbers are considered. There is at least a four-parameter family of different linear ambient velocity distributions, but nevertheless a comprehensive set of results for the transfer rate may be compiled by combining previously published work with some new developments. Some of these are exact results for particular linear ambient flow fields and some are approximate results for classes of linear flow fields.For small Péclet number (P), the non-dimensional additional transfer rate due to convection is equal to αN20P½, where N0 is the Nusselt number for P = 0 and the proportionality constant α is a parameter of the concentration distribution due to a steady point source in the given linear ambient flow field. A general method of determining α is developed, and numerical values are found for some particular linear ambient flow fields. It is estimated that the value of α for any linear ambient flow field in which the vorticity does not dominate the straining motion lies within 10% of 0·34 when P is defined in terms of a particular invariant of the ambient rate-of-strain tensor E.At large Péclet number the transfer rate N depends on the velocity distribution near the particle, and attention is restricted to the case of a sphere in low-Reynolds-number flow. For a rigid sphere $N = \beta P^{\frac{1}{3}}$ for any ambient pure straining motion, and the Levich concentration-boundary-layer method may be used to show that β = 0·90 for both axisymmetric and two-dimensional ambient pure straining, and probably for any other pure straining motion, when P is suitably defined. When the ambient vorticity ω is non-zero, the sphere rotates, and the Levich method cannot be used. However, it is shown that the part of the velocity distribution that varies sinusoidally with the azimuthal angle around the rotation axis does not affect the transfer rate and that N is asymptotically the same as for an ambient axisymmetric pure straining motion with rate of extension in the direction of the axis of symmetry equal to Eω(= ω. E. ω/ω2). In the exceptional case Eω = 0, N approaches a constant as P → ∞.It is possible to interpolate between the asymptotic relations for small and large Péclet number with comparatively little uncertainty for any ambient pure straining motion and for any linear ambient flow field in which ω and Eω are non-zero.

scholarly journals Cross-Flow Tidal Turbines with Highly Flexible Blades—Experimental Flow Field Investigations at Strong Fluid–Structure Interactions

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 797
Author(s):  
Stefan Hoerner ◽  
Iring Kösters ◽  
Laure Vignal ◽  
Olivier Cleynen ◽  
Shokoofeh Abbaszadeh ◽  
...  
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Cross Flow ◽  
Speed Ratio ◽  
Fluid Structure Interactions ◽  
Dimensional Parameter ◽  
Fluid Structure ◽  
Passive Flow Control ◽  
Tidal Turbines ◽  
Tidal Turbine

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single tip-speed ratio (equal to 2), the key non-dimensional parameter describing the operating point, and solidity (equal to 1.5), quantifying the robustness of the turbine shape. Both parameters are standard values for cross-flow tidal turbines. Those lead to highly dynamic characteristics in the flow field dominated by dynamic stall. The flow field is investigated at the blade level using high-speed particle image velocimetry measurements. Strong fluid–structure interactions lead to significant structural deformations and highly modified flow fields. The flexibility of the blades is shown to significantly reduce the duration of the periodic stall regime; this observation is achieved through systematic comparison of the flow field, with a quantitative evaluation of the degree of chaotic changes in the wake. In this manner, the study provides insights into the mechanisms of the passive flow control achieved through blade flexibility in cross-flow turbines.

Fan Performance Scaling With Inlet Distortions

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
J. J. Defoe ◽  
M. Etemadi ◽  
D. K. Hall
Keyword(s):  
Design Flow ◽  
Flow Coefficient ◽  
Axial Fan ◽  
Fan Performance ◽  
Physical Mechanisms ◽  
Viscous Losses ◽  
Performance Scaling ◽  
Large Distortion ◽  
Stator Blade ◽  
Primary Focus

Applications such as boundary-layer-ingesting (BLI) fans and compressors in turboprop engines require continuous operation with distorted inflow. A low-speed axial fan with incompressible flow is studied in this paper. The objectives are to (1) identify the physical mechanisms which govern the fan response to inflow distortions and (2) determine how fan performance scales as the type and severity of inlet distortion varies at the design flow coefficient. A distributed source term approach to modeling the rotor and stator blade rows is used in numerical simulations in this paper. The model does not include viscous losses so that changes in diffusion factor are the primary focus. Distortions in stagnation pressure and temperature as well as swirl are considered. The key findings are that unless sharp pitchwise gradients in the diffusion response, strong radial flows, or very large distortion magnitudes are present, the response of the blade rows for strong distortions can be predicted by scaling up the response to a weaker distortion. In addition, the response to distortions which are composed of nonuniformities in several inlet quantities can be predicted by summing up the responses to the constituent distortions.

Sign in / Sign up

Export Citation Format

Share Document