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.

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

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.

scholarly journals Numerical Simulation of the Effects of the Helical Angle on the Decaying Swirl Flow of the Hole Cleaning Device

Processes ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 109 ◽  
Author(s):  
Jingyu Qu ◽  
Tie Yan ◽  
Xiaofeng Sun ◽  
Zijian Li ◽  
Wei Li
Keyword(s):  
Flow Direction ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Critical Value ◽  
Swirl Flow ◽  
Swirl Number ◽  
Hole Cleaning ◽  
Helical Angle ◽  
Swirl Intensity ◽  
Cleaning Device

The application of the hole cleaning device in downhole is a new technology that can improve the problem of cuttings accumulation in the annulus and improve the hole cleaning effect of the wellbore during drilling. In this paper, the Reynolds Averaged Navier–Stokes model, together with the Realizable k-ε turbulence model, are used to perform transient simulations. The effects of rotational speed, blade shape, and helical angle on the initial swirl intensity and its decay behavior along the flow direction are studied. The swirl number, the initial swirl intensity, the decay rate, the tangential velocity distribution, and the variation of pressure are analyzed. The results indicate that the swirl number of the swirl flow exponentially decays along the flow direction. The straight blade and V-shaped blade have different swirl flow induction mechanisms. Under specific drilling parameters, the critical helical angle is determined for both types of blades. When the selection of the helical angle is close to the critical value, the swirl flow will be close to the axial flow, which is of little help in hole cleaning. Moreover, the rotation direction of swirl flow will change when the helical angle exceeds the critical value.

Lift and Drag Characteristics of an Air-Cooled Heat Exchanger Axial Flow Fan

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Francois G. Louw ◽  
Theodore W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Heat Exchanger ◽  
Lift Coefficient ◽  
Axial Flow ◽  
Design Flow ◽  
Low Flow ◽  
Axial Fan ◽  
Flow Rates ◽  
Blade Element Theory ◽  
Lift And Drag ◽  
Air Cooled Heat Exchanger

Actuator-disk models (ADMs) use blade element theory to numerically simulate the flow field induced by axial fans. These models give a fair approximation at near design flow rates, but are of poor accuracy at low flow rates. Therefore, the lift/drag (LD) characteristics of two-dimensional (2D) sections along the span of an air-cooled heat exchanger (ACHE) axial fan are numerically investigated, with the future prospect of improving ADMs at these flow conditions. It is found that the blade sectional LD characteristics are similar in shape, but offset from the 2D LD characteristics of the reference airfoil (NASA LS 413 profile) at small angles of attack (αatt<5deg). A deviation between these characteristics is observed at higher angles of attack. The blade sectional lift coefficients for αatt>5deg always remain lower compared to the maximum lift coefficient of the reference airfoil. Conversely, the blade sectional drag coefficients are always higher compared to that of the reference airfoil for αatt>5deg.

Flow instability in a volute-free centrifugal fan subjected to non-axisymmetric pre-swirl flow from upstream bended inflow tube

2021 ◽  
pp. 095765092110626
Author(s):  
Zhengfeng Liu ◽  
Hui Yang ◽  
Haijiang He ◽  
Peiquan Yu ◽  
Yikun Wei ◽  
...  
Keyword(s):  
Static Pressure ◽  
Flow Instability ◽  
Pressure Fluctuations ◽  
Pressure Rise ◽  
Internal Flow ◽  
Temporal Variations ◽  
Swirl Flow ◽  
Incoming Flow ◽  
Centrifugal Fan ◽  
Local Flow

The characteristics of internal flow and performance of a centrifugal fan is greatly dependent on the inflow pattern. As the fan is subjected to incoming flow from an upstream tube, the size and geometry of the tube affect the three-dimensional motion of local flow and possibly degrades the aerodynamic performance of the fan. In this work, we performed a numerical investigation on the internal flow in a centrifugal fan subjected to incoming flow from an upstream bended inflow tube of various radii using the steady and unsteady Reynolds-averaged Navier-Stokes (RANS and URANS) simulation approaches. The effects of the non-axisymmetric pre-swirl flow generated due to the curvature of the bended inflow tube are demonstrated by analyzing the internal flow characteristics of the fan, including the spatial distributions and temporal variations of pressure field and streamlines, pressure fluctuations in the upstream tube, the inflow and outflow sections of the impeller, and the circumferential distributions of velocity and pressure in the impeller. The numerical results reveal that as the inflow tube is curved with larger curvature (smaller radius of the bended section), the pre-swirl inflow is strong and deteriorates the static pressure rise and static pressure efficiency of the centrifugal fan more remarkably, and the circumferential non-uniformity of pressure and velocity distributions appears inside of the channels of the fan. As the radius of the bended section increases, the instability of the internal flow gets more pronounced, as represented by the stronger pressure fluctuations at the inflow and outflow sections. The prediction capabilities of RANS and URANS approaches are also analyzed based on the numerical data and we found that the latter is more reliable in predicting the performance of the fan.

Influence on the Axial Flow Fan Aerodynamic Characteristic Due to an Introduction of Internal Secondary Flow

2008 ◽  
Author(s):  
Matjazˇ Eberlinc ◽  
Brane Sˇirok ◽  
Marko Hocˇevar ◽  
Matevzˇ Dular
Keyword(s):  
Standardized Test ◽  
Flow Direction ◽  
Axial Flow ◽  
Performance Testing ◽  
Internal Flow ◽  
Suction Side ◽  
Flow Conditions ◽  
Axial Fan ◽  
Trailing Edge ◽  
Local Characteristics

Axial fans often show adverse flow conditions at the fan hub and at the tip of the blades. Modification of conventional axial fan blades is presented. Hollow blades were manufactured from the hub to the trailing edge at the tip of the blades. Hollow blades enabled the formation of self-induced internal flow through internal passages. The internal flow enters the internal radial flow passages of the hollow blades through the openings near the fan hub and exits through the tip trailing edge slots. Study of the influence of internal flow on the flow field of axial fan and modifications of axial fan aerodynamic characteristics is presented. The characteristics of the axial fan with the internal flow were compared to characteristics of a geometrically equivalent fan without internal flow. The results show integral measurements of performance testing using standardized test rig, and the measurements of local characteristics. The measurements of local characteristics were performed with a hot-wire anemometry, five-hole probe and computer-aided visualization. We attained reduction of adverse flow conditions near the blade tip trailing edge, boundary-layer reduction on the blade suction side and reduction of flow separation. Introduction of the self-induced blowing led to the preservation of external flow direction, defined by blade geometry and enabled maximal local energy conversion. The integral characteristic reached higher degree of efficiency.

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 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.

A Study on the Ventilation Efficiency Improved by Airflow Characteristics of the Axial Fan Installed in Parallel at the Side Wall of the Narrow Exhaust Tower

2016 ◽  
Vol 24 (04) ◽  
pp. 1650026
Author(s):  
Yong-Il Kwon
Keyword(s):  
Numerical Study ◽  
Flow Direction ◽  
Ventilation System ◽  
Side Wall ◽  
Pulse Method ◽  
Swirl Flow ◽  
Numerical Results ◽  
Axial Fan ◽  
Ventilation Efficiency ◽  
Parking Lot

A numerical study has been conducted to simulate airflow and ventilation characteristics in the exhaust tower installed to ventilation of the multi-story underground parking lot. It is the objective of the present study to identify ventilation problems and to suggest the flow direction modifications of the ventilation system with the axial fan to improve ventilation efficiency in the low-rise section of the exhaust tower. Numerical results on SVE4 (scale of ventilation efficiency NO.4) and local mean age of exhaust ports are presented along with the location of axial fan on the direction of swirl flow and the dimension of exhaust tower. Ventilation system modifications on the direction of swirl flow have been suggested from the numerical results in order to prevent the flow interference by airflow discharged from the adjacent stories. The overall ventilation efficiency according to the rotational condition of the axial fans are compared quantitatively using the concept of SVE4 calculated by means of tracer gas pulse method to investigate distribution characteristics of the air discharged from each story among the exhausted air to the two exhaust ports in the narrow exhaust tower.

scholarly journals Movement of a finite body in channel flow

2016 ◽  
Vol 472 (2191) ◽  
pp. 20160164 ◽  
Author(s):  
Frank T. Smith ◽  
Edward R. Johnson
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Flow Instability ◽  
Flow Direction ◽  
Finite Size ◽  
The Body ◽  
Thin Body ◽  
Shear Stresses ◽  
Unsteady Interaction ◽  
High Reynolds

A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be cos ⁡ ( π / 7 ) , i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.

Influence of the Blade-Spoke Connection Point on the Aerodynamic Performance of Darrieus Wind Turbines

2016 ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
Giovanni Ferrara ◽  
Lorenzo Ferrari
Keyword(s):  
Wind Turbines ◽  
Design Parameter ◽  
Flow Direction ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Common Solution ◽  
Curvature Effects ◽  
Flow Curvature ◽  
Low Incidence

The assessment of robust CFD techniques is casting new light on the aerodynamics of airfoils rotating around an axis orthogonal to flow direction, with particular reference to flow curvature effects and stall mechanisms. In particular, Darrieus wind turbines’ designers are taking profit from these new discovers to improve the aerodynamic design of the rotors, in view of an increase of the overall efficiency and a reduction of the structural stresses on the blades. A controversial design parameter for Darrieus turbines, especially in case of small-size rotors, is represented by the location of the blade-spoke connection along the chord. The most common solution is indeed to place the connection at approximately airfoil’s quarter chord, i.e. where the pressure center is commonly located for low incidence angles. In some cases, however, the blade is connected at middle chord due to symmetry or aesthetic reasons. In some small turbines, innovative designs have even disregarded this parameter. Even if one can argue that the blade connection point is about to have some aerodynamic effects on the turbine’s performance, the real impact of this important design parameter is often not fully understood. The present study makes use of extensive CFD simulations on a literature case study, using a NACA 0021 airfoil, to assess the influence of the blade-spoke connection point. In particular, the differences in terms of power coefficient curve of the turbine, optimal tip-speed ratio, torque profiles and stresses on the connection are analyzed and discussed. Detailed flow analyses are also shown for azimuthal positions of particular interest. Results on the selected case study showed that the middle-chord blade-spoke connection point seems to guarantee a higher performance of the rotor, even if additional solicitation is applied to the connection itself. It is further shown that the same performance can indeed be obtained with the airfoil attached at quarter chord and properly pitched. By doing so, the stresses are contained and the performance is maximized.

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