High Resolution Velocity Measurements Upstream and Downstream of an Axial Flow Fan Rotor (original) (raw)
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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.
Aerodynamic effects of forward blade skew in axial flow rotors of controlled vortex design
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2007
Comparative studies have been carried out on two axial flow fan rotors of controlled vortex design (CVD), at their design flowrate, in order to investigate the effects of circumferential forward skew on blade aerodynamics. The studies were based on computational fluid dynamics (CFD), validated on the basis of global performance and hot wire flow field measurements. The computations indicated that the forward-skewed blade tip modifies the rotor inlet condition along the entire span, due to its protrusion to the relative inlet flow field. This leads to the rearrangement of spanwise blade load distribution, increase of losses along the dominant part of span, and converts the prescribed spanwise blade circulation distribution towards a free vortex flow pattern. Due to the above, reduction in both total pressure rise and efficiency was established. By moderation of the radial outward flow on the suction side, being especially significant for nonfree vortex blading, forward sweep was found to be particularly useful for potential reduction of near-tip loss in CVD rotors. Application of reliable CFD-based design systems was recommended for systematic consideration and control of both load-and loss-modifying effects due to nonradial blade stacking.
Relative flow and turbulence measurements within and downstream of an axial flow rotor
Experimental Thermal and Fluid Science, 1994
• This article presents the results of an experimental investigation on the relative flow within and behind an axial fan rotating row. The flow within the rotor passages has been surveyed over blade-to-blade surfaces with a laser-Doppler velocimeter (LDV), while the flow leaving the rotating blades has been measured by means of stationary hot-wire probes and fastresponse miniature pressure transducers. A phase-locked sampling and ensemble-averaged technique has been applied to separate periodic and random contributions from the instantaneous signals of the different stationary measuring instruments. Within the rotor both axial and tangential velocity components and the related variances have been measured by rotation of the single-channel laser-Doppler optics operating in back-scatter mode. In the plane aft of the rotor all mean velocity and Reynolds stress components of the relative flow have been determined using a 12-orientations single-sensor hot-wire technique. The static and relative total pressure distributions have been obtained from the velocity components and the ensemble-averaged total pressure distributions given by the fastresponse miniature pressure transducers. The results, shown in terms of secondary vector plots and contours of mean flow characteristics, turbulence intensity, and Reynolds stress components, give a detailed picture of the rotor flow kinematic structure and of the relative total pressure loss and turbulence distributions.
Experimental and Computational Assessment of a Ducted-Fan Rotor Flow Model
Journal of Aircraft, 2012
Ducted-fan-based vertical and/or short takeoff and landing uninhabited aerial vehicles are frequently encountered in aeronautical applications. In edgewise flight, the performance of these vehicles is, in general, poor because of the increasingly distorted inlet flow as the flight speed is increased. The present experimental study uses a planar particle image velocimeter system to investigate the near duct aerodynamic performance in hover and edgewise flight conditions. High-resolution particle image velocimetry measurements provide reliable and highresolution aerodynamic data forming a validation basis for further analytical and computational design studies. A radial equilibrium-based fan aerodynamic model is also integrated into a three-dimensional Reynold-averaged-Navier-Stokes-based computational system. Particle image velocimetry measurements and computational predictions of the mean flow near the fan inlet plane are in very good agreement at hover conditions. The aerodynamic modifications due to fan inlet flow distortion in an edgewise flight regime are clearly displayed in particle image velocimetry results. A comparison of the current particle image velocimetry measurements and the accelerated Reynold-averaged-Navier-Stokes predictions supported by the simple radial equilibrium-based rotor model indicates that the current rotor model can be highly effective and time efficient in the design cycle of future vertical and/or short takeoff and landing uninhabited aerial vehicle systems based on ducted fans.
Computational characterization of an axial rotor fan
Journal of Energy Systems, 2017
Axial flow fans are broadly applied in numerous industrial applications because of their simplicity, compactness and moderately low cost, such us propulsion machines and cooling systems. Computational fluid dynamics techniques are commonly applied to investigate flow phenomena through the axial fan and the rotor dynamic performance. In the present work, a computational model of an axial fan is presented in the current study. Numerical simulations of a single stage axial fan on variable conditions have been performed to obtain the detailed flow field of the centrifugal fan. The investigation of the current work is focused on the rotor–stator configuration and the modeling of aerodynamic behavior of the blade rows. The precise prediction of axial force and efficiency has essential implication for the optimized operation of axial fan and the choice of thrust bearing. Furthermore, it can act as guide for the geometrical and structural axial fan design and the study of axial force predic...
Experimental and Numerical Investigation onto 1250mm Axial Fan
Applied Mechanics and Materials, 2012
Numerical simulation is of interest for most fan designers to optimize the fan designs. Computational fluid dynamic (CFD) has become an essential tool in almost every branch of fluid dynamics and one of the major tools for fan designs. As the fan designers relying on the numerical simulation, the accuracy of tools such as CFD in predicting the performance has become a subject of interest. This paper validates the CFD modeling of an axial fan design against experimental result. The experimental rig and test procedure are developed with reference to “AMCA standard 210”. The analysis is conducted on 1250mm diameter axial fan with two different blade pitch angle 30° and 40°. Prior to encounter the swirling effect and deflection of velocity vector due to rotor blade, a stator blade with the same profile as rotor blade is used as the outlet guide vanes in opposite direction. The computational model is created according to the experimental condition and applied realistic boundary condition...
12th European Conference on Turbomachinery Fluid Dynamics and hermodynamics
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.
Visualization of tip vortex flow in an open axial fan by EFD
Journal of Visualization, 2002
The behavior of tip vortex in an axial fan without casing wall (called open axial fan) was discussed and analyzed. The velocity measurement was performed by using two-compon ents Laser Doppler Velocimetry (LDV) system. The detailed velocity and vorticity distribution inside blade passage and downstream of rotor were obtained. Thus the structure of tip vortex and its behavior were graphically visualized by experimental fluid dynamics (EFD). The tip vortex flow trace was indicated with the calculation of vorticity. As a result, it was found that tip vortex was generated at blade tip region near leading edge and it extended to downstream of blade exit with its core tending inward to hub direction. In addition, leading edge vortex was also found at the forepart of the experimental open fan.
Experimental Thermal and Fluid Science, 2011
The purpose of this work is to study the effects of blade thickness on the performances of an axial-flow fan. Two fans that differ only in the thickness of their blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin blades. The second fan has much thicker blades compatible with the rotomoulding conception process. The overall performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus flow-rate) is slightly steeper for the fan with thick blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick blades fan is lower than the efficiency of the fan with thin blades but remains high on a wider flow-rate range. The mean velocity fields downstream of the rotors are very similar at nominal points with less centrifugation for the thick blades fan. Moreover, the thick blades fan maintains an axial exit-flow on a wider range of flow-rates. The main differences concern local properties of the flow: Phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick blades fan that for the thin blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.
Thermoanemometrical Study of Flow Structure Through a Centrifugal Fan
Mechanics and Control, 2013
Recognition of the spatial kinematics of the flow domain and its relation to the fan impeller geometry has a key influence on the machine design and better performance parameters. In this work some experimental results are presented of the measurements of the absolute velocity, its components and turbulence of the air flow through the radial fan rotor operating in various configurations. As the main measuring tool a three-axial hot-wire anemometer (CTA) probe has been used. The anemometer cooperates with a specialized software prepared by the authors for the spatial analysis of the flow field considered. In particular, the distribution of the circumferential velocity components behind the impeller rim has been examined, which affects directly the fan efficiency. As a result of the flow analysis behind the rotor rim a relationship has been established between the degree of turbulence and the machine efficiency. On the basis of the changes in the averaged-in-time velocity field behind the rim, the outflow of air from the blade passage has been evaluated.