scholarly journals Investigation of the turbulent swirl flows in a conical diffuser

2010 ◽  
Vol 14 (suppl.) ◽  
pp. 141-154 ◽  
Author(s):  
Miroslav Benisek ◽  
Dejan Ilic ◽  
Djordje Cantrak ◽  
Ivan Bozic
Keyword(s):  
Flow Parameter ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Swirl Flow ◽  
Experimental Investigations ◽  
Test Bed ◽  
Axial Fan ◽  
Swirl Flows ◽  
Conical Diffuser ◽  
Flow Loss

Results of the theoretical and experimental investigations of the turbulent mean swirl flows characteristics change along straight conical diffuser of incompressible fluid (air) are presented in this paper. The main swirl flow characteristics review is given. In addition: the specific swirl flow energy, the energy loss, the mean circulation, the swirl flow parameter, the ratio between the swirl and axial flow loss coefficients change along the diffuser are presented. Among other values: the Boussinesq number, outlet Coriolis coefficient and swirl flow loss coefficient dependences on inlet swirl flow parameter are also given. The swirl flow specific energy and outlet Coriolis coefficient calculation procedure are presented in this paper, as well as experimental test bed and measuring procedures. The swirl flow fields were induced by the axial fan impeller. Various swirl parameters were achieved by the impeller openings and rotational speeds.

scholarly journals Experimental investigations of the turbulent swirl flow in straight conical diffusers with various angles

2017 ◽  
Vol 21 (suppl. 3) ◽  
pp. 725-736 ◽  
Author(s):  
Dejan Ilic ◽  
Miroslav Benisek ◽  
Djordje Cantrak
Keyword(s):  
Flow Parameter ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Swirl Flow ◽  
Experimental Investigations ◽  
Axial Fan ◽  
Flow Loss ◽  
Inlet Swirl ◽  
Loss Coefficients ◽  
Total Divergence

Results of experimental investigations of the turbulent swirl flow in three straight conical diffusers with various diffuser total angles are presented in this paper. All three diffusers have the inlet diameter 0.4 m and total divergence angles 8.6?, 10.5?, and 12.6?. The incompressible swirl flow field is generated by the axial fan impeller, and for each diffuser several regimes were achieved by changing rotation number. Original classical probes were used for measurements. The distributions of the average main swirl flow characteristics along the diffuser are shown. Distributions of the inlet Boussinesq number, outlet Coriolis coefficient, ratio of the swirl and completely axial flow loss coefficients at conical diffuser on the inlet swirl flow parameter are also presented.

scholarly journals Integral and statistical characteristics of the turbulent swirl flow in a straight conical diffuser

2018 ◽  
Vol 45 (2) ◽  
pp. 127-137 ◽  
Author(s):  
Dejan Ilic ◽  
Djordje Cantrak ◽  
Novica Jankovic
Keyword(s):  
Laser Doppler Anemometry ◽  
Volume Flow Rate ◽  
Swirl Flow ◽  
Statistical Characteristics ◽  
Experimental Investigations ◽  
Outer Diameter ◽  
Axial Fan ◽  
Conical Diffuser ◽  
Measuring Section ◽  
Total Divergence

The results of the experimental investigations of the turbulent swirl flow in a straight conical diffuser with inlet diameter 0.4m and total divergence angle 8.6? are presented in this paper. The incompressible swirl flow field is generated by the axial fan with outer diameter 0.397m. The measurements were performed in one measuring section downstream the axial fan impeller in the conical diffuser in position (z/R0 = 1) with original classical probes and an one-component laser Doppler anemometry (LDA) system, for four flow regimes. The comparative measurements of axial and circumferential velocities are presented. The Reynolds number, calculated on the basis of the average velocity, ranges from 149857 to 216916. Integral parameters, such as volume flow rate, average circulation and swirl number, are determined. Statistical characteristics, such as level of turbulence, skewness and flatness factors, are calculated. The highest levels of turbulence for axial velocity are reached in region 0.4 < r/R < 0.6, where D = 2R. The highest levels of turbulence for circumferential velocity are reached for the regimes with lower circulation in r/R ? 0.4, i.e., in the vortex core region for the cases with higher circulation.

Laser Insight Into the Turbulent Swirl Flow Behind the Axial Flow Fan

2014 ◽  
Author(s):  
Đorđe S. Čantrak ◽  
Novica Janković ◽  
Milan R. Lečić
Keyword(s):  
Vortex Core ◽  
High Speed ◽  
Isotropic Turbulence ◽  
Laser Doppler Anemometry ◽  
Measurement Techniques ◽  
Swirl Flow ◽  
Test Rig ◽  
Axial Fan ◽  
Mean Velocity ◽  
Swirl Flows

Complex experimental study of the turbulent swirl flow behind the axial fan is reported in this paper. Axial fan with nine blades, designed to generate Rankine vortex, was positioned in the circular pipe entrance transparent section with profiled free bell mouth inlet. Two test rigs were built in order to study the turbulent swirl flow generated on the axial fan pressure side in the case of axially unrestricted and restricted swirl flows. One-component laser Doppler anemometry (LDA) and stereo particle image velocimetry (SPIV) were used in the first test rig in the measuring section 3.35D, measured from the test rig inlet. One of the latest measurement techniques, high speed SPIV (HSS PIV), was used for the measurements in the second test rig in the section 2.1D downstream the fan’s trailing edge. Achieved Reynolds numbers in the first test rig are Re = 182600 and 277020, while in the second Re = 186463. Turbulent velocity field non-homogeneity and anisotropy is revealed using the LDA system. Calculated turbulent statistical properties, such as moments of the second and higher orders, reveal complex mechanisms in turbulent swirl flow. It is shown for the used axial fan construction that swirl number has almost constant value for two various duty points generated by changing rotation number. Study of the instant and mean velocity fields obtained using SPIV discovers vortex core dynamics. Obtained percentage of the unique positions of the total velocity minimum are 10% for the first regime, while 11.5% for the second regime in the first test rig. HSS PIV experimental results have also shown the three-dimensionality and non-homogeneity of generated turbulent swirl flow. Experimentally determined and calculated invariant maps revealed three-component isotropic turbulence in the vortex core region.

Experimental Study of the Effect of Serrations on Axial Flow Fan Blade Trailing Edge

2016 ◽  
Author(s):  
Dhyanjyoti Deb Nath ◽  
K. Viswanath ◽  
Ankit Bhai Patel
Keyword(s):  
Axial Velocity ◽  
Pressure Sensors ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Experimental Investigations ◽  
Spanwise Direction ◽  
Axial Fan ◽  
Trailing Edge ◽  
Trailing Edges ◽  
Fan Blade

Rotor wakes shed from a compressor rotor impinge on downstream blades and is a major source of rotor-stator interaction noise and much research has been dedicated on wake attenuation. Serrated trailing edges is one such wake attenuation technique where the vortices produced at the serrated trailing edges enhance mixing and create a more uniform flow at stator inlet. The present paper investigates the effect of serrations on the trailing edge of a forced vortex axial fan blade. Experimental investigations were carried out at rotor outlet using pneumatic probes and fast response pressure sensors. It is found that total and static pressures reduce in serrated blades due to reduced turning and hence reduced work input. The absolute tangential velocity wake deficit decreases in serration valleys and improvement in axial velocity wake deficit is also found. Improvements as large as 19% and 18% decrease in absolute tangential velocity and axial velocity wake deficit are found at certain radii. The spanwise shape of the wake is altered by the serrations and a wake pattern undulating in the spanwise direction is observed. These are expected to bring down the circumferential variation of the velocity and its phase before entering the next row of blades and bring down the tonal noise.

scholarly journals Influence of Chord Lengths of Splitter Blades on Performance of Small Axial Flow Fan

2015 ◽  
Vol 9 (1) ◽  
pp. 361-370
Author(s):  
Guoqi Li ◽  
Lifu Zhu ◽  
Yongjun Hu ◽  
Yingzi Jin ◽  
Toshiaki Setoguchi ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Axial Flow ◽  
Internal Flow ◽  
Leading Edge ◽  
Chord Length ◽  
Aerodynamic Noise ◽  
Axial Fan ◽  
Axial Flow Fan ◽  
Suction Surface ◽  
Small Axial Flow Fan

On the basis of small axial fan with five blades, 6 types of small axial flow fans with different chord lengths splitter blades were designed. Numerical simulation of 6 fan models with splitter blades and prototype fan were done by using Fluent. Based on the obtained simulation results, internal flow characteristics and aerodynamic noise were analyzed and compared. It indicates that: splitter blades with suitable chord length have improved significantly on internal flow characteristics, which inhibits backflow from pressure surface to the suction surface at blade tip and leading edge and restrains flow separation. The 6 model fans are better than prototype fan on aerodynamic noise improvement, but too long or too short chord lengths are both disadvantage to improve aerodynamic noise. The results reveal that 2/6, 3/6 and 4/6 chord length model have relatively better acoustic characteristics and internal flow characteristics. The research program will offer a reference for structural improvements and noise reduction on small axial flow fan.

scholarly journals Novel methods for axial fan impeller geometry analysis and experimental investigations of the generated swirl turbulent flow

2010 ◽  
Vol 14 (suppl.) ◽  
pp. 125-139 ◽  
Author(s):  
Zoran Protic ◽  
Milos Nedeljkovic ◽  
Djordje Cantrak ◽  
Novica Jankovic
Keyword(s):  
Standardized Test ◽  
Laser Doppler Anemometry ◽  
Swirl Flow ◽  
Experimental Investigations ◽  
Operating Characteristics ◽  
Axial Fan ◽  
Axial Velocity Component ◽  
Impeller Blade ◽  
Hydraulic Machinery ◽  
Geometry Analysis

Geometry analysis of the axial fan impeller, experimentally obtained operating characteristics and experimental investigations of the turbulent swirl flow generated behind the impeller are presented in this paper. Formerly designed and manufactured, axial fan impeller blade geometry (originally designed by Prof. Dr-Ing. Z. Protic?) has been digitized using a threedimensional (3D) scanner. In parallel, the same impeller has been modeled by beta version software for modeling axial turbomachines, based on modified classical calculation. These results were compared. Then, the axial fan operating characteristics were measured on the standardized test rig in the Laboratory for Hydraulic Machinery and Energy Systems, Faculty of Mechanical Engineering, University of Belgrade. Optimum blade impeller position was determined on the basis of these results. Afterwards, the impeller with optimum angle, without outlet vanes, was positioned in a circular pipe. Rotational speed has been varied in the range from 500 till 2500rpm. Reynolds numbers generated in this way, calculated for axial velocity component, were in the range from 0,8?105 till 6?105. LDA (Laser Doppler Anemometry) measurements and stereo PIV (Particle Image Velocimetry) measurements of the 3D velocity field in the swirl turbulent fluid flow behind the axial fan have been performed for each regime. Obtained results point out extraordinary complexity of the structure of generated 3D turbulent velocity fields.

An analysis on the flow characteristics of bi-directional axial-flow pump under reverse operation

2017 ◽  
Vol 231 (3) ◽  
pp. 239-249 ◽  
Author(s):  
Pengfei Ma ◽  
Jun Wang
Keyword(s):  
Flow Characteristics ◽  
Axial Flow ◽  
Internal Flow ◽  
Optimum Operating ◽  
Reverse Direction ◽  
Guide Vanes ◽  
Flow Loss ◽  
Axial Flow Pump ◽  
Object Of Study ◽  
Flow Pump

When the conventional bent guide vanes are applied to the bi-directional axial-flow pump, its performance declines considerably under reverse operation. Regarding a bi-directional axial-flow pump with high specific speed as the object of study, the variation of both hydraulic performance and internal flow field under reverse operation are analyzed in this paper. The results indicate that both the head and efficiency of the pump will drop greatly and the optimum operating point lean to the lower flow rate when it operates in the reverse direction, mainly due to the prewhirl caused by the guide vanes; the shedding vortex is formed after flow separation occurred near the trailing edge of blade, and its scale keeps increasing in the diffusing pipe during its motion until it collapses in the straight pipe, which is the major causes of the big flow loss and significant decline of the performance under reverse operation.

Parmeterization of the Total Pressure Distribution Along a Low-Pressure Axial Fan Blade According to the Design Requirements

2008 ◽  
Author(s):  
Maria Pascu ◽  
Philipp Epple ◽  
Antonio Delgado ◽  
Franz Durst
Keyword(s):  
Total Pressure ◽  
Design Method ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Critical Parameters ◽  
Design Strategies ◽  
Axial Fan ◽  
Absolute Increase ◽  
Overall Performance ◽  
Fan Blade

In the field of axial flow turbomachines, the two–dimensional cascade model is often used experimentally or numerically to investigate fundamental flow characteristics and overall performance of the impeller. The core of the present work is a design method for axial fan cascades aiming to derive inversely the optimum blade shape based on the requirements of the impeller and not using any predefined airfoil profiles. While most design strategies based on the airfoil theory assume constant total pressure at all streamlines, i.e. free–vortex flow, this paper investigates the possibility of varying the total pressure along the blade and based on that, an analytical expression of the outlet blade angle is determined. When computing the blade profile at specified radius, critical parameters reflecting on the flow characteristics are observed and adjusted, i.e. sufficient lift and controlled deceleration of the flow on the contour so that the resulting profile is derived for minimum losses. The validation of this design strategy is given by the numerical results obtained when employed as an optimization tool for an industrial fan: 10–20% absolute increase in the efficiency of the optimized impeller.

Performance Degradation and Flow Instability of Axial-Flow Fan Due to Upstream Obstacle

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Donghyuk Kang ◽  
Takeru Shinohara ◽  
Shinsaku Nakamura ◽  
Koichi Nishibe ◽  
Kotaro Sato ◽  
...  
Keyword(s):  
Pressure Loss ◽  
Flow Instability ◽  
Flow Direction ◽  
Axial Flow ◽  
Swirl Flow ◽  
Performance Degradation ◽  
Low Flow ◽  
Power Coefficient ◽  
Centrifugal Fan ◽  
Axial Fan

Abstract This paper elucidates the performance degradation and flow instability of an axial fan caused by the presence of disk-shaped obstacles upstream of the fan, such as wall surfaces. The increase in pressure loss and the decrease in shaft power coefficient due to inlet swirl flow, and the increase in pressure loss due to the outlet swirl flow, cause performance degradation. When the obstacle is closer to the fan, the strong swirl flow causes a negative pressure region between the fan and the obstacle, reversing the flow direction. This phenomenon is caused by the diffuser effect of the outward flow and the increase in pressure by acting as a multiblade centrifugal fan. At a low flow rate, a clockwise vortex is generated at the center of the obstacle and induces two counterclockwise rotating vortices. The vortices circumferentially separate the inward and outward flows along the fan's axis in a uniform manner, and their cores are circularly rotated by the clockwise vortex. These findings can contribute to the layout of fans under spatial restriction and suppression of flow instability due to obstacles.

scholarly journals Analytical and numerical investigation of the optimum pressure distribution along a low-pressure axial fan blade

2008 ◽  
Vol 223 (3) ◽  
pp. 643-657 ◽  
Author(s):  
M Pascu ◽  
M Miclea ◽  
P Epple ◽  
A Delgado ◽  
F Durst
Keyword(s):  
Total Pressure ◽  
Design Method ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Critical Parameters ◽  
Design Strategies ◽  
Axial Fan ◽  
Optimum Pressure ◽  
Absolute Increase ◽  
Fan Blade

In the field of axial flow turbomachines, the two-dimensional cascade model is often used experimentally or numerically to investigate fundamental flow characteristics and overall performance of the impeller. The core of the present work is a design method for axial fan cascades aiming to derive inversely the optimum blade shape based on the requirements of the impeller and not using any predefined aerofoil profiles. While most design strategies based on the aerofoil theory assume constant total pressure at all streamlines, i.e. free-vortex flow, this paper investigates the possibility of varying the total pressure along the blade and based on that, an analytical expression of the outlet blade angle is determined. When computing the blade profile at a specified radius, critical parameters reflecting on the flow characteristics are observed and adjusted (i.e. sufficient lift and controlled deceleration of the flow on the contour) so that the resulting profile is derived for minimum losses. The validation of this design strategy is given by the numerical results obtained when employed as an optimization tool for an industrial fan: 10–20 per cent absolute increase in the static efficiency of the optimized impeller.

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