Visualization of tip vortex flow in an open axial fan by EFD (original) (raw)
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Experimental investigation of tip-leakage flow in an axial flow fan at various flow rates
Journal of Mechanical Science and Technology, 2019
Casing pressure measurements and Stereoscopic Particle-Image Velocimetry (SPIV) measurements are used together to characterize the behavior of the rotor tip leakage flow at both the design and near-stall conditions in a low-speed multistage axial compressor. A three-dimensional Navier-Stokes solver is also performed for the multistage compressor and the prediction of tip leakage flow is compared with SPIV data and casing dynamic static pressure data. During the experiment 10 high-frequency Kulite transducers are mounted in the outer casing of the rotor 3 to investigate the complex flow near the compressor casing and Fourier analyses of the dynamic static pressure on the casing of the rotor 3 are carried out to investigate the tip leakage flow characteristics. At the same time, the two CCD cameras are arranged at the same side of the laser light sheet, which is suitable for investigating unsteady tip leakage flow in the multistage axial compressor. The SPIV measurements identify that the tip leakage flow exists in the rotor passage. The influence of tip leakage flow leads to the existence of low axial velocity region in the rotor passage and the alternating regions of positive and negative radial velocity indicates the emergence of tip leakage vortex (TLV). The trajectory of the tip leakage vortex moves from the suction surface toward the pressure surface of adjacent blade, which is aligned close to the rotor at the design point (DP). However, the tip leakage vortex becomes unstable and breaks down at the near-stall point (NS), making the vortex trajectory move upstream in the rotor passage and causing a large blockage in the middle of the passage.
Comprehensive Study on Tip Vortex with Lateral Jet Flow
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2003
Comprehensive numerical and experimental investigations of tip vortical characteristics were conducted for lateral tip jet flow over a fixed wing as a step to reduce blade vortex interaction noise. The tip vortex of a NACA0012 blade was measured and visualized for the fundamental study of tip vortical flow, and the results were compared with numerical data as a validation of numerical solvers. Three-dimensional compressible Euler/Navier-Stokes codes were used to calculate the effect of jet flow from the tip of an OLS (modified BHT 540) fixed blade at various freestream velocities and jet conditions. The results show that the jet flowing from the wing tip can diffuse the tip vortex enlarging the core size of tip vortex and weakening its strength. When applied to the blade vortex interaction phenomena, this enlarged and weak vortex can produce a lower pressure gradient on the blade surface, which means that the jet flow can effectively reduce blade vortex interaction noise.
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.
High Resolution Velocity Measurements Upstream and Downstream of an Axial Flow Fan Rotor
2008
An important topic of research at The Budapest University of Technology and Economics, Department of Fluid Mechanics is that of axial flow fans of controlled vortex design. In this ongoing research, a computational fluid dynamics simulation has been developed for the further investigation of the flow phenomena developing in the vicinity of the rotor. In order to fully validate this simulation, detailed velocity measurements have been carried out on the flow both upstream and downstream of a rotor designed using a controlled vortex design method incorporating circumferential forward skew. These measurements have already been used in order to validate the pitchwise averaged data of the computational fluid dynamics simulation, with this article focusing on the validation of the pitchwise resolved data.
Experimental Investigation on Aerodynamic Characteristics of an Axial Flow Fan
The prime objective of this work is to determine the relationship between the mechanical and aerodynamic characteristics of the fan when the blade position is default and when it is changed and to find out which position gives optimum output at given power and given working conditions and according to the change of environment. In this experiment, the aerodynamic characteristic of an axial flow fan is going to be determined by measuring the static and total pressures in the suction and discharge sides of the fan for various flow rates. In this experiment, for different blade angle, flow velocity is measured and relationship between the change of blade angles and the flow velocity are plotted
The Effect of Tip End-Blade Geometry on the Axial Fans Performance
A numerical study is carried out to investigate the effect of the addition of winglet to the end of blade on the axial fan performance. Validation and assessment of the used computer program FLUENT 6.2, is carried out by comparing its result with previous researcher. Simulation is then carried out to analyze the flow pattern with and without a winglet attached to the fan blade. Velocity distribution produced numerically showed that the winglet suppresses the secondary flow at the tip gap. Pressure distributions also confirmed the winglet advantages. Calculated performance of the fan used showed general increase of the fan efficiency with 3.5% above those without winglet at the optimum efficiency point and with up to 6 % at off design point.. 1. INTRODUCTION Fans demand minimum gaps in order to facilitate operation, this gap tip clearance flow is known to have detrimental effects on the axial fans performance. The static pressure difference between the suction and the pressure side o...
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.
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.
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.
ICFD11-EG-4099 THE EFFECT OF TIP END-BLADE GEOMETRY ON THE AXIAL FANS PERFORMANCE
A numerical study is carried out to investigate the effect of the addition of winglet to the end of blade on the axial fan performance. Validation and assessment of the used computer program FLUENT 6.2, is carried out by comparing its result with previous researcher. Simulation is then carried out to analyze the flow pattern with and without a winglet attached to the fan blade. Velocity distribution produced numerically showed that the winglet suppresses the secondary flow at the tip gap. Pressure distributions also confirmed the winglet advantages. Calculated performance of the fan used showed general increase of the fan efficiency with 3.5% above those without winglet at the optimum efficiency point and with up to 6 % at off design point.