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.

Influence of the Sweep Stacking on the Performance of an Axial Fan

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Ayhan Nazmi Ilikan ◽  
Erkan Ayder
Keyword(s):  
Pressure Rise ◽  
Secondary Flows ◽  
Axial Fan ◽  
Negative Effects ◽  
Blade Loading ◽  
Stall Margin ◽  
Negative Effect ◽  
Aerodynamic Parameters ◽  
Overall Performance ◽  
Positive Effect

In modern turbomachinery blade design, nonradial stacking of the profiles is often assumed to be one of the ways to improve the performance of a machine. Instead of stacking the profiles radially, the stacking line is changed by several modifications such as sweep, dihedral, lean, or a combination of these. Nonradial stacking influences secondary flows that have effects on the aerodynamic parameters such as efficiency, pressure rise, blade loading, and stall margin. However, many of the studies in literature are limited by the comparison of two or three cases. This situation leads to conflicting results because a modification may cause a positive effect in one study while in another one, the same modification may have a negative effect. In this study, a modified free vortex axial fan (named as base fan (BF) for this study) is designed first and the profiles of the blades are stacked radially by joining the centroids of the profiles. Second, 45 deg, 30 deg forward sweep (FS) and backward sweep (BS) modifications are applied. The effects of these modifications on aerodynamic performance of the fans are investigated by means of numerical calculations. The results show that FS and BS do not significantly affect the overall performance of the fan at the design flowrate in spite of the occurring modifications of the local blade pressure distribution. However, at low flowrates, FS and BS have positive and negative effects on the fan performance, respectively.

Numerical Simulation of the Axial Fan Performance Degradation Due to Sand Ingestion

2002 ◽  
Author(s):  
A. Ghenaiet ◽  
S. C. Tan ◽  
R. L. Elder
Keyword(s):  
Lift Coefficient ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
Performance Degradation ◽  
Tip Clearance ◽  
Sand Particle ◽  
Axial Fan ◽  
Stall Margin ◽  
Static Pressure Distribution ◽  
Aerodynamic Lift

This paper presents a method based on Lieblein and Koch correlations for assessing the performance degradation of an axial fan due to sand ingestion. The method is based on mean line analysis, and predicted aerodynamic performance includes the adiabatic efficiency, pressure rise coefficient and stall margin. Changes to the blade geometry which affect the fan aerodynamic performance are mainly due to erosion which reduces the blade chord and increases the tip clearance and surface roughness. Erosion damage has a significant effect on the aerodynamic lift coefficient, which is related to the static pressure distribution. An in-house developed trajectory code, combined with restitution factors and an erosion model (applicable for cast aluminium alloy and stainless steel), was used to predict particle trajectories and the amount of material removed. The method was applied successfully to a contra-whirl axial fan where reasonably good agreement was found between predicted and experimental results. Tests were conducted with MIL-E 5007E sand particle sizes of between 0.0 and 1000.0 microns. A method for predicting life expectancy of the fan is also presented. The methodology shows that critical blade parameters necessary for performance degradation simulation can be successfully obtained in this way.

Aerodynamics of Contra-Rotating Fans With Swept Blades

2015 ◽  
Author(s):  
K. Vijayraj ◽  
M. Govardhan
Keyword(s):  
Rotational Speed ◽  
Axial Flow ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
The Other ◽  
Flow Structures ◽  
Current Investigation ◽  
Rotating System ◽  
Stall Margin ◽  
Static Head

A Counter-Rotating System (CRS) is composed of a front rotor and a rear rotor which rotates in the opposite direction. Compared with traditional rotor-stator system, the rear rotor is used not only to recover the static head but also to supply energy to the fluid. Therefore, to achieve the same performance, the use of a CRS may lead to a reduction of the rotational speed and may generate better homogeneous flow downstream of the stage. On the other hand, the mixing area in between the two rotors induces complicated interacting flow structures. Blade sweep has attracted the turbomachinery blade designers owing to a variety of performance benefits it offers. However, the effect of blade sweep on the performance, stall margin improvements whether it is advantageous/disadvantageous to sweep one or both rotors has not been studied till now. In the current investigation blade sweep on the performance characteristics of contra rotating axial flow fans are studied. Two sweep schemes (axial sweeping and tip chord line sweeping) are studied for two sweep angles (20° and 30°). Effect of blade sweep on front rotor and rear rotor are dealt separately by sweeping one at a time. Both rotors are swept together and effect of such sweep scheme on the aerodynamic performance of the stage is also reported here. The performance of contra rotating fan is significantly affected by all these parameters. Blade sweep improved the pressure rise and stall margin of front rotors. Axially swept rotors are found to have higher pressure rise with reduced incidence losses near the tip for front rotors. Sweeping the rear rotor is not effective since the pressure rise is less than that of unswept rotor and also has less stall margin.

Assessment of a Novel Non-Axial Counter-Rotating Compressor Concept for Aero-Engines

2018 ◽  
Author(s):  
Quentin Dejour ◽  
Huu Duc Vo
Keyword(s):  
Pressure Rise ◽  
Axial Direction ◽  
Boundary Layer Separation ◽  
Low Flow ◽  
Compressor Stage ◽  
Mixed Flow ◽  
Stall Margin ◽  
High Loss ◽  
Multi Stage ◽  
Flow Compressor

This paper presents the first assessment of a new non-axial counter-rotating compressor concept. This concept consists of replacing the stator of a mixed-flow compressor stage or the diffuser of a centrifugal compressor stage with a counter-rotating rotor that will turn the flow back to the axial direction with much lower diffusion factor, while providing the equivalent in work of the upstream mixed-flow rotor or impeller. This concept has two advantages. First, the very high stage pressure rise means that only a single counter-rotating rotor may be required, making mechanical implementation simpler than for multi-stage axial counter-rotating compressors. Second, the replacement of the high flow turning (high loss) stator/diffuser in a non-axial stage with a low flow turning counter-rotating rotor gives the new concept potential for achieving higher efficiency than conventional non-axial compressors. As a first proof of concept, a subsonic counter-rotating mixed-flow compressor and its conventional (i.e. rotor-stator) equivalent have been designed with the intent of being implemented in a test rig. CFD simulations have been carried out for a comparative evaluation of both configurations. Results show that the counter-rotating mixed-flow compressor produces more than double the pressure rise of its conventional version with a slightly higher peak-efficiency while having a smaller axial length. Moreover, the counter-rotating configuration has a better stall margin than its conventional counterpart, for which the boundary layer separation from excessive flow turning in the stator causes early stall.

scholarly journals Effect of Two- and Three-Dimensionally Designed Guide Vanes with Different Camber Length on Static Pressure Recovery of a Wall-Mounted Axial Fan

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1595
Author(s):  
Yong-In Kim ◽  
Yong-Uk Choi ◽  
Cherl-Young Jeong ◽  
Kyoung-Yong Lee ◽  
Young-Seok Choi
Keyword(s):  
Flow Rate ◽  
Guide Vane ◽  
Dynamic Pressure ◽  
Pressure Rise ◽  
Design Flow ◽  
Low Flow ◽  
Axial Fan ◽  
Flow Angle ◽  
Numerical Effort ◽  
Vane Angle

This study was based on a numerical effort to use the motor support (prop) as a guide vane when the motor of a wall-mounted axial fan was located at the fan outlet while maintaining the structural and spatial advantage. The design for the guide vane followed two- and three-dimensional methods. The inlet vane angle, meridional length (total), and meridional length with a vane angle of zero (0) degrees (linear) were considered as design variables. At the design and some low flow rate points, the 2D design offered the most favorable performance when the meridional length with a vane angle of zero (0) degrees (linear) was 30% based on total length, and was the worst for 70%. The 3D design method applied in this study did not outperform the 2D design. In the 2D design concept, averaging the flow angle for the entire span at the design flow rate could ensure a better pressure rise over a more comprehensive flow rate range than weighting the flow angle for a specific span. In addition, the numerical results were validated through an experimental test, with an important discussion of the swirl (dynamic pressure) component. The influence of the inlet motor and turbulence model are presented as a previous confirmation.

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.

Understanding the Flow Behavior in a Low Hub-Tip Ratio, High Aspect Ratio Contra-Rotating Axial Fan Stage

2012 ◽  
Author(s):  
Chetan S. Mistry ◽  
A. M. Pradeep
Keyword(s):  
Aspect Ratio ◽  
Total Pressure ◽  
Numerical Study ◽  
Flow Behavior ◽  
Experimental Studies ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Speed Ratio ◽  
Axial Fan ◽  
Stall Margin

This paper discusses the results of a parametric study of a pair of contra-rotating axial fan rotors. The rotors were designed to deliver a mass flow of 6 kg/s at 2400 rpm. The blades were designed with a low hub-tip ratio of 0.35 and an aspect ratio of 3.0. Numerical and experimental studies were carried out on these contra-rotating rotors operating at a Reynolds number of 1.25 × 105 (based on blade chord). The axial spacing between the rotors was varied between 50 to 120 % of the chord of rotor 1. The performance of the rotors was evaluated at each of these spacing at design and off-design speeds. The results from the numerical study (using ANSYS CFX) were validated using experimental data. In spite of certain limitations of CFD under certain operating conditions, it was observed that the results agreed well with those from the experiments. The performance of the fan was evaluated based on the variations of total pressure, velocity components and flow angles at design and off-design operating conditions. The measurement of total pressure, flow angles etc. are taken upstream of the first rotor, between the two rotors and downstream of the second rotor. It was observed that the aerodynamics of the flow through a contra rotating stage is significantly influenced by the axial spacing between the rotors and the speed ratio of the rotors. With increasing speed ratios, the strong suction generated by the second rotor, improves the stage pressure rise and the stall margin. Lower axial spacing on the other hand, changes the flow incidence to the second rotor and thereby improves the overall performance of the stage. The performance is investigated at different speed ratios of the rotors at varying axial spacing.

Axial-Flow Ventilation Fan Design Through Multi-Objective Optimization to Enhance Aerodynamic Performance

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Jin-Hyuk Kim ◽  
Jae-Woo Kim ◽  
Kwang-Yong Kim
Keyword(s):  
Multiobjective Optimization ◽  
Axial Flow ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
Low Flow ◽  
Total Efficiency ◽  
Objective Functions ◽  
Maximum Increase ◽  
Design Variables ◽  
Ventilation Fan

This paper presents an optimization procedure for axial-flow ventilation fan design through a hybrid multiobjective evolutionary algorithm (MOEA) coupled with a response surface approximation (RSA) surrogate model. Numerical analysis of a preliminary fan design is conducted by solving three-dimensional (3-D) Reynolds-averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) turbulence model. The multiobjective optimization processes are performed twice to understand the coupled effects of diverse variables. The first multiobjective optimization process is conducted with three design variables defining stagger angles at the hub, mid-span, and tip, and the second is conducted with five design variables defining hub-to-tip ratio, hub cap installation distance, hub cap ratio, and the stagger angles at the mid-span and tip. Two aerodynamic performance parameters, the total efficiency and total pressure rise, are selected as the objective functions for optimization. These objective functions are numerically assessed through 3-D RANS analysis at design points sampled by Latin hypercube sampling in the design space. The optimization yields a maximum increase in efficiency of 1.8% and a 31.4% improvement in the pressure rise. The off-design performance is also improved in most of the optimum designs except in the region of low flow rate.

On the Effects of Incidence Angle on the Mean Wake of a Surface-Mounted Finite-Height Square Prism

2015 ◽  
Author(s):  
Ayodele Ogunremi ◽  
David Sumner
Keyword(s):  
Incidence Angle ◽  
Flow Direction ◽  
Ground Plane ◽  
Vortex Pair ◽  
Tip Vortex ◽  
Pressure Probe ◽  
Mean Velocity ◽  
Square Prism ◽  
Finite Height ◽  
The Mean

The wake of a surface-mounted finite-height square prism of sub-critical aspect ratio AR = 3 was studied experimentally in a low-speed wind tunnel at a Reynolds number of Re = 3.7×104. The ratio of the boundary layer thickness on the ground plane, to the width of the prism, was δ/D = 1.5. The incidence angle of the prism was varied from α = 0° to 45°. Wake mean velocity measurements were made in vertical planes normal to and parallel to the main flow direction using a seven-hole pressure probe. As the prism is rotated from α = 0° to 45°, the mean wake progressively widens and the maximum streamwise extent of the mean recirculation zone increases. The mean streamwise tip vortex pair is symmetric at 0° and 45°, but becomes strongly asymmetric at intermediate α, where the tip vortex is found higher above the ground plane on the wider side of the wake. The wake and tip vortex asymmetry is most pronounced near the critical incidence angle.

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.

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