Aerodynamic effects of forward blade skew in axial flow rotors of controlled vortex design (original) (raw)
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Analysis and Validation of Blade with Skewed Angle for Axial Fan
The main aim of this research is to investigate the impact with a point of skew on the blade of the axial fan by calculating mass flow, rotor velocity, and pressure acting on the fluid by the fan's blade to obtain optimal efficiency. It has been observed that fluctuations in mass flow due to higher rotational speed (rpm) lead to an uneven distribution of the outlet speed of the flow line located in the ventilation hole of the stator, leading to a lower noise level. The mass flow rate is directly proportional to the performance, and pressure drop of the axial fan. The present work is carried out by considering a range of angles of (0º to 6º) for its rotor blade using trial and error in the CFD technique, we observe the axial fan handles the good volume of air at relatively low pressure and delivers good efficiency in the output airflow. Consequently, the axial fan is designed to operate on high static pressure. This manuscript consists of the computation of the aerodynamic performances of symmetrical blade profiles of a fully axial fan by Computational Fluid Dynamics (CFD) methods, developing a methodology for the design of axial fans, and analysis of the designed fan with CFD methods.
INVESTIGATION EFFECTS OF BACKWARD AND FORWARD BLADE SKEW MODES APPLIED TO AXIAL FLOW TURBO MACHINERY
IRJET, 2022
Since the three-dimensional (3D) Computational fluid dynamic (CFD) flow field investigation techniques, as well as advanced flow measurement tools, give potential to predict effects related to blade skew to consider them in blade design. Through the use of CFD tools and the analysis of experimental data that has been published in the literature, the effects of skew applied to the rotor of axial flow turbo engines were examined in this work. Low-aspect-ratio rotors with forward and backward skew have been investigated, and their performance has been compared to that of un-skew datum rotors at various flow rates, span wise positions, and overall efficiency. In this work, the blade sections are swept forward and backward with 3.5 degree and 2.082 degree for dihedral as comparison with data in research and development (R&D) in the field of axial flow turbo machinery (such as fan, compressor, pump) at nowadays. It is focuses on isolated rotors of fluid transporting machines to improve the rotor performance characteristics via the beneficial modification on blade aerodynamics, by means of appropriate modification of blade geometry. Nowadays, the enhanced computational resources allow the designer to realize blade design concepts being more sophisticated and complicated than the “classic” designs, e.g. incorporating blade sweep with aid of Computational Fluid Dynamics (CFD) simulations. Three- dimensional (3D) CFD flow field investigation techniques, as well as advanced flow measurement tools, give potential to predict effects related to blade sweep and skew to consider them in blade design. It was noted that FSK provides a greater efficiency up to 75% of the blade span at the design point, demonstrating the advantages of FSK rotors over other rotors. Near the tip and at smaller radii, the forward-skewed blade increased and decreased inlet axial velocities, respectively.. Due to the small skew angles, the three rotors nearly have similar outlet axial velocities performance. The axial velocity also increases along the dominant part of the span. At the design flow rate, the forward skew considerably reduces the radically outward flow along the span and mostly near the tip.
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.
2013
The main feature of a Reversible jet fan is to provide the same air flow and thrust in both directions of flow, keeping the maximum ratio thrust-power in any range of electrical motor power. These conditions could be achieved with the use of a rotor formed by double-symmetric airfoils, for example, an elliptical airfoil. This paper present a rotor blade design of a reversible axial rotor of a jet fan usually used for ventilation of road tunnels, the design is based on a methodology that utilizes a non-free vortex condition for resolving the radial equilibrium equation. This project was developed with reference in certain data available in the literature of elliptical profiles arranged in linear cascades representing axial rotors, gotten by means of computational fluid dynamics tools. Moreover, the characteristics of aerodynamic performance of the reversible axial rotor were found either in the design point or out of this for a specific rotation using Computational Fluid Dynamics Met...
EFFECTIVENESS OF BLADE FORWARD SWEEP IN A SMALL INDUSTRIAL TUBE-AXIAL FAN
SUMMARY Forward swept blades in low-speed axial fan rotors allow for appreciable gain in the stall margin and a small percentage gain in the maximum fan efficiency if the rotor blade circulation increases from the hub to tip. However, a reduction of the fan pressure at the design point counteracts these advantages. The paper investigates the effectiveness for small tube-axial fans of a design method suggested to increase the performance of an existing arbitrary vortex design by introducing the span-wise uniform distribution of blade forward sweep. The following three rotors for a 315-mm tube-axial fan have been tested: unswept, forward swept, and forward swept with additional sweep at the blade tip. Experimental data prove the effectiveness of the design method for these small fans.
International Journal of Rotating Machinery, 2011
The flow field at the rotor exit of a low aspect ratio axial flow fan for different tip geometries and for different flow coefficients is measured in the present study. The following configurations are tested: (1) rotor without partial shroud, designated as rotor (wos), (2) rotor with partial shroud, designated as rotor (ws), and (3) rotor with perforated (perforations in the shape of discrete circular holes) partial shroud, designated as rotor (wps). From steady state measurements, the performance of rotor (wps) is found to be the best. Both the rotors with partial shrouds have stalled at a higher flow coefficient compared to that of rotor (wos). From periodic flow measurements, it is concluded that the low velocity region near the tip section is considerably reduced with the use of partial shrouds with perforations. The extent of this low velocity region for both rotor (wos) and rotor (wps) increases with decreasing flow coefficient due to increased stage loading. This core of low...
Axisymmetric Analysis and Design of Ducted Rotors
This report describes the analytical formulation used for the design and analysis of a ducted propulsor with single or multiple blade rows. It is based on a lifting-line representation of the rotor blade together with an axisymmetric panel representation of the duct and centerbody. The induced velocities associateed with blade-row loading are represented by vortex sheets shed into the flowfield. Blade element models are used for blade row sections using two-dimensional lift, moment and profile drag characteristics to account for loading and viscous losses. The modeling fidelity of the present approach lies between classical vortex/blade-element methods of Betz [1] and Glauert [2], and a general 3-D vortex-lattice or panel method. Even the general 3-D formulations would have to make the same time-averaging assumptions for the unsteady counterrotating flow as the present method, and hence would not be more sophisticated or more accurate in this regard. The chief advantage of the present method is that it is extremely fast computationally and is has simple inputs, making it ideal for interactive design work.
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.
2012
This work presents a methodology for aerodynamic design of axial flow pump rotors based on initial values established. This methodology proposes a modification next to the blade tip region, in order to minimize the effects caused by the spacing between the blade tip and the casing (tip clearance) in the flow of axial flow rotors. One is the displacement of the blade profiles near to the blade tip region. These displacements are known as sweep and dihedral. An axial flow pump rotor was designed and a certain tip clearance was fixed. This conventional rotor was then modified and applied the sweep and dihedral in the region near to the blade tip. By means of techniques of computational fluid dynamics (CFD), the search for the optimal value of efficiency was made through the CRSA optimizer with Fortran platform that manages the system of mesh generation with the numerical simulation software, FLUENT ®. Based on the optimal values found, a restriction of range of sweep and dihedral was p...
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...