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Aerodynamic and Aeroacoustic Performance of a Skewed Rotor
Abstract
This paper presents an experimental investigation and numerical simulation of the aerodynamic and aeroacoustic performance of an axial-flow fan with skewed rotating blades in the design and off-design operation. The blade is designed with a forward skew angle for which the stacking line is directed towards the rotating direction on the circumferential section. A detailed investigation of a three-dimensional flow field in the inter-blade row and passage using five-hole probes and a hot-wire anemometer at the upstream and downstream locations of the rotors has been carried out and compared with a fan with unskewed rotor blades. Noise testing was performed in the anechoic chamber. The experiments were performed at three rotating speeds. Aerodynamic curves show that the performance of the skewed blade increased at a higher pressure rise of 13.1% and gave a larger flow rate of about 5% and a higher efficiency of more than 3%. The higher efficiency in the skewed rotor was due to the practical and advantageous spanwise redistribution of aerodynamic parameters, a greater boundary movement into the main flow, a secondary flow reduction and the thinness of the rotor wake. Aeroacoustic performance and frequency spectra in almost the whole frequency domain showed a noise reduction of 2 to 4 dBA in the skewed fan. Lower noise in the skewed blade comes from the broadband noise reduction owing to a thinner wake layer, a phase difference in rotor radiation and tip leakage noise reduction. A wider stall margin for more than 20% is obtained in the skewed blade due to the proportional distribution of aerodynamic parameters. The three-dimensional Navier-Stokes approach is simulated in the inner blade flow.
... In the design of turbomachinery blades [4][5][6][7][8][9][10], the use of sweep, lean, and skew (stacking line in rotational direction) in the axial flow compressor rotor has recently become a matter of interest. These blade shape parameters are normally added to minimize shock losses, corner separation in the blade hub and tip clearance losses in the transonic compressor rotor, creating a three-dimensional stacking line. ...
... There have been a variety of research conducted on the benefits of a distorted rotor. Cai, et al. [10] researched the aerodynamic and aeroacoustic characteristics of a skewed blade axial flow fan. With the reduction of the secondary flow and the thinness of the rotor wake, the broadband noise was reduced. ...
Blade-shape design was one of the potential objects to delay stall inception and surge. This paper presents the effects of blade-shape design on the aerodynamic performance of a single-stage transonic axial compressor using three-dimensional Reynolds-averaged Navier-Stokes equations with the k-ε turbulence model. Validation of numerical model for a single-stage transonic axial compressor, NASA Stage 36, was conducted to evaluate the computational fluid dynamics method. A parametric study of the blade-shape was performed for leading-edge and trailing-edge blade angles at rotor tip of NASA Stage 36. The numerical results show that the compressor for the case of leading-edge angle could reach the maximal stall margin of 11.342% as compared with the reference value (7.111%), and the compressor stable range extension raised remarkable as compared with the smooth casing by 52,634% while peak adiabatic efficiency slightly changed.
... Ces instationarités ont un impact direct sur le bruit généré et apportent un élément de réponse pour la réduction de bruit observée pour les ventilateur (+). Les essais menés par Cai et al. [38], montrent en revanche des résultats bien meilleurs pour un empilement (+) en terme d'élévation de pression (+13%), de plage de débit (+5%), de rendement (+3%) et également en terme de performances acoustiques (-2 à -4 dB). Cai et al. [38] s'intéressent de plus à la zone de décrochage où de nouveau l'empilement (+) permet de meilleures performances aérodynamiques et acoustiques en élargissant la zone de fonctionnement stable. ...
... Les essais menés par Cai et al. [38], montrent en revanche des résultats bien meilleurs pour un empilement (+) en terme d'élévation de pression (+13%), de plage de débit (+5%), de rendement (+3%) et également en terme de performances acoustiques (-2 à -4 dB). Cai et al. [38] s'intéressent de plus à la zone de décrochage où de nouveau l'empilement (+) permet de meilleures performances aérodynamiques et acoustiques en élargissant la zone de fonctionnement stable. ...
Recently, the need for smaller axial fans with high specific speeds lead to the design of counter-rotating axial fans. The design of this kind of machines, which have promising aerodynamic performances, suffers from a lack of knowledge about their aerodynamics. Counter-rotating rotors, widely studied in aeronautics, are an effective alternative to conventional machines and offer many advantages: rotation ratio and diameter reduction, and high flexibility in use. However, a better understanding of their working and of the rotors interaction is required to enhance their design and to make them widely integrated in current applications. This experimental research work investigates on a ducted counter-rotating stage designed with a home code, MFT based on an inverse design method for rotors and rotor-stator stages, and to which a rapid and simple method is implemented to design the rear rotor. The study focuses on the effects of the rotation ratio and on the axial spacing between rotors. It highlights several aspects of the rotors interaction through global performance and local unsteady measurements. This dissertation is organized in four parts: rotor-stator and rotor-rotor stages design; design of the experimental facility, AERO²FANS allowing global performance and local unsteady measurements; comparison between the two stages and design validation; investigation on the effects of the rotation ratio and the axial spacing on the global and the local performances.
... Recently, the use of sweep, lean (dihedral), and skew (stacking line in rotational direction) in axial flow compressor rotor has become a matter of interest in the design of turbomachinery blades [4][5][6][7][8][9][10]. These blade shape parameters, which form a three-dimensional stacking line, are generally introduced to reduce shock losses, corner separation in the blade hub, and tip clearance losses in transonic compressor rotor. ...
... A number of studies have been done on the advantages of a skewed rotor. Cai, et al. [9] studied on aerodynamic and aeroacoustic characteristics of an axial flow fan with skewed blade. With the reduction of a secondary flow and the thinness of a rotor wake, they reduced a broadband noise. ...
Shape optimization of a transonic axial compressor rotor operating at the design flow condition has been performed using the response surface method and three-dimensional Navier-Stokes analysis. The three design variables, blade sweep, lean and skew, are introduced to optimize the three-dimensional stacking line of the rotor blade. The objective function of the shape optimization is adiabatic efficiency. Throughout the shape optimization of the rotor, the adiabatic efficiency is increased by reducing the hub corner and tip losses. Separation line due to the interference between a passage shock and surface boundary layer on the blade suction surface is moved downstream for the optimized blade compared to the reference one. Among the three design variables, the blade skew is most effective to increase the adiabatic efficiency in the compressor rotor.
... The use of sweep, lean (dihedral), and skew (stacking line in rotational direction) in axial flow compressor rotor has become a matter of interest in the design of turbomachinery blades [23][24][25][26][27][28][29]. The blade shape parameters which are used to construct a threedimensional stacking line is generally introduced to reduce shock losses, corner separation in the blade hub, and tip clearance losses in transonic compressor rotor. ...
... There are a number of studies on the advantages of a skewed rotor. Cai, et al. [28] studied on aerodynamic and aero-acoustic characteristics of an axial flow fan with skewed blade. With the reduction of a secondary flow and the thickness of a rotor wake, they could reduce a broadband noise. ...
Recent development of high speed computers and use of optimization techniques have given a big momentum of turbomachinery design replacing expensive experimental cost as well as trial and error approaches. The surrogate based optimization techniques being used for aerodynamic turbomachinery designs coupled with Reynolds-averaged Navier-Stokes equations analysis involve single- and multi-objective optimization methods. The objectives commonly tried to improve were adiabatic efficiency, pressure ratio, weight etc. Presently coupling the fluid flow and structural analysis is being tried to find better design in terms of weight, flutter and vibration, and turbine life. The present article reviews the surrogate based optimization techniques used recently in turbomachinery shape optimizations.
... The performance of axial fans is influenced by many factors [3][4][5]. Cai et al. [6] presented their experimental investigations and numerical simulations of the performance of a deflected-blade axial flow fan. They showed that compared to radial blades, forwardswept blades could increase pressure by 13.1%, boost flow by about 5%, reduce noise by 2-4 dB, and increase efficiency by 3%. ...
Nuclear grade axial flow fans are widely used in nuclear power plants for ventilation and heat dissipation and have the advantages of high efficiency and high flow rates. A nuclear grade axial flow fan with OGVs (outlet guide vanes) can recover the kinetic energy of the dynamic impeller outlet winding to increase the ventilator pressure, thus improving the ventilator efficiency; therefore, the OGVs play an essential role in the performance of the axial flow fan. Based on accurate numerical simulations, an MRGP approximation model was developed to analyse the factors affecting the OGVs duct and optimise the guide vane structure, combined with the Sobol method for sensitivity analysis. The experiments and numerical simulations show that the total pressure of the optimised model increases by 154 Pa, and the noise decreases by 4.1 dB. The multi-objective optimisation method using the parametric approach and combining it with the MRGP model is highly reliable. It provides a key design direction for optimising nuclear grade axial flow fans.
... The use of sweep, lean (dihedral), and skew (shifting stacking line in rotational direction) in an axial flow compressor rotor has become a matter of interest in the design of turbomachinery blades by many researchers ( Gallimore et al, 2002;Denton and Xu, 2002;Cai et al., 2003;Fisher et al., 2003;and Benini, 2004). These blade shape parameters, which form a three-dimensional stacking line, are generally introduced to reduce shock losses, corner separation in the blade hub, and tip clearance losses in transonic compressor rotors. ...
Numerical optimization with hybrid multiple objectives evolutionary algorithm (hybrid MOEA) is carried out for design of an axial compressor blade. Two conflicting objectives, i.e., total pressure ratio and adiabatic efficiency are optimized with three design variables concerning sweep, lean and skew of blade stacking line. At the data points generated by D-optimal design, the objectives are calculated by three-dimensional Reynolds-averaged Nervier-Stokes analysis. Elitist non-dominated sorting of genetic algorithm (NSGA-II) with ε-constraint local search strategy of hybrid MOEA is used for multi-objective optimization. Both objective function values are found to be improved as compared to the reference blade by multi-objective optimization. The flow analysis results show the mechanism for the improvement of blade performance. INTRODUCTION Recently, several efforts have been made to improve performance of turbomachinery blade applying optimization algorithms in assistance with the computational power replacing hit and trial approach and expensive experimental setup. Application of optimization methods has reduced the computational cost sharply for predicting the better design of turbomachines to enhance the performance in terms of reducing weight and flow loss, enhancing efficiency, pressure and surge margin, etc. by changing shape of stacking line, camber profile, etc. The use of sweep, lean (dihedral), and skew (shifting stacking line in rotational direction) in an axial flow compressor rotor has become a matter of interest in the design of turbomachinery blades by many researchers
... Deformation of stacking line using sweep, lean, and skew has become a matter of interest in the design of turbomachinery blades by many researchers (Gallimore et al., 2002;Denton and Xu, 2002;Cai et al., 2003;Fisher et al., 2003;Benini, 2004). These blade shape parameters, which form a three-dimensional stacking line, are generally introduced to reduce shock losses, corner separation in the blade hub, and tip clearance losses in axial turbomachines. ...
This work presents numerical optimization for design of a blade stacking line of a low speed axial flow fan with a fast and elitist Non-Dominated Sorting of Genetic Algorithm (NSGA-II) of multi-objective optimization using three-dimensional Navier-Stokes analysis. Reynolds-averaged Navier-Stokes (RANS) equations with k-ε turbulence model are discretized with finite volume approximations and solved on unstructured grids. Regression analysis is performed to get second order polynomial response which is used to generate Pareto optimal front with help of NSGA-II and local search strategy with weighted sum approach to refine the result obtained by NSGA-II to get better Pareto optimal front. Four geometric variables related to spanwise distributions of sweep and lean of blade stacking line are chosen as design variables to find higher performed fan blade. The performance is measured in terms of the objectives; total efficiency, total pressure and torque. Hence the motive of the optimization is to enhance total efficiency and total pressure and to reduce torque.
... The use of sweep, lean (dihedral), and skew (shifting stacking line in rotational direction) in an axial flow compressor rotor has become a matter of interest in the design of turbomachinery blades by many researchers [1][2][3][4][5]. These blade shape parameters, which form a three-dimensional stacking line, are generally introduced to reduce shock losses, corner separation in the blade hub, and tip clearance losses in transonic compressor rotors. ...
Numerical optimization with multiple objectives is carried out for design of an axial compressor blade. Two conflicting objectives,
total pressure ratio and adiabatic efficiency, are optimized with three design variables concerning sweep, lean and skew of
blade stacking line. Single objective optimizations have been also performed. At the data points generated by D-optimal design,
the objectives are calculated by three-dimensional Reynolds-averaged Navier-Stokes analysis. A second-order polynomial based
response surface model is generated, and the optimal point is searched by sequential quadratic programming method for single
objective optimization. Elitist non-dominated sorting of genetic algorithm (NSGA-II) with ε-constraint local search strategy
is used for multi-objective optimization. Both objective function values are found to be improved as compared to the reference
one by multi-objective optimization. The flow analysis results show the mechanism for the improvement of blade performance.
... However, there was poor performance in aerodynamics of the backward-swept blades. Cai et al. [2] presented an experimental investigation and numerical simulation of the performance of an axial-flow fan with skewed rotating blades. The results showed that the performance of the forward-skewed blade increased at a higher pressure rise of 13.1% and gave a larger flow rate of about 5%, as well as a higher efficiency of more than 3% and a lower noise of 2 to 4 dBA. ...
This paper presents an experimental study of the optimization of blade skew in low pressure axial
fan. Using back propagation (BP) neural network and genetic algorithm (GA), the optimization was
performed for a radial blade. An optimized blade is obtained through blade forward skew. Measurement of
the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the
radial blade, the optimized blade demonstrated improvements in efficiency, total pressure ratio,
stable operating range, and aerodynamic noise. Detailed flow measurement was performed in outlet
flow field for investigating the responsible flow mechanisms. The optimized blade can cause
a spanwise redistribution of flow toward the blade midspan and reduce tip loading. This results in
reduced significantly total pressure loss near hub and shroud endwall region, despite the slight
increase of total pressure loss at midspan. In addition, the measured spectrums show that the
broadband noise of the impeller is dominant.
This chapter describes optimization techniques for maximizing industrial fluid machinery performance. Both single‐ and multi‐objective methods are explained in detail that are capable of dealing with both single‐ and/or multi‐point problems. The most common and relevant problem type concerns shape optimization of machine stationary and rotating parts. Regardless of the type of problem formulation, fluid machinery shape optimization is typically performed using an iterative computer loop that always involves an optimization engine, a flow solver, and a parametric model of the machine shape. The chapter implicitly refers to the loop architecture as the “baseline loop structure” and explores pump optimization. Centrifugal pumps are dealt with as they are the most general case in terms of geometrical complexity followed by axial‐flow and mixed‐flow pump optimization. Compressor and turbine optimization is described, and optimizations of fans, hydraulic turbines, and other types are also discussed.
This work presents a numerical optimization procedure for a low-speed axial flow fan blade with weighted average surrogate model. Reynolds-averaged Navier-Stokes equations with SST turbulence model are discretized by finite volume approximations and solved on hexahedral grids for flow analyses. The blade profile as well as stacking line is modified to enhance blade total efficiency, i.e., the objective function. Six design variables related to blade lean and blade profile are selected, and a design of experiments technique produces design points where flow analyses are performed to obtain values of the objective function. PBA model is employed as a surrogate model for optimization. A search algorithm is used to find the optimal design in the design space from the constructed surrogate model for the objective function. As a main result, the efficiency is increased effectively by the present optimization procedure.
Shape optimization of a rotor blade in a single-stage transonic axial compressor has been performed using a response surface method and three-dimensional Navier-Stokes analysis. Two shape variables of the rotor blade, which are used to define a blade skew, are introduced to increase an adiabatic efficiency. Throughout the shape optimization of a rotor blade, the adiabatic efficiency is increased to about 2.2 percent compared to that of the reference shape of the stator. The increase in efficiency for the optimal shape of the rotor is due to the pressure enhancement, which is mainly caused by moving the separation position on the suction surface of rotor blade to the downstream direction.
The effect of rotor blade installation angle on the flow field and performance of axial flow fan is presented in this paper. CFD simulation and experimental investigations are carried out with different value of installation angle. First, the inner flow fields of axial fan were simulated and analyzed by using the RNG k-? turbulent model and sliding mesh method of Fluent 6.3 software. Then, a five-hole probe was employed to measure the inner flow field of axial fan, and the variation tendency of velocity and pressure in testing section are found in good agreement with numerical results. The research shows that: with the increasing of installation angle, the lower pressure area induced by impact loss decreases in pressure side, but if installation angle is reduced, the impact loss happened in suction side will be more serious and the wake loss will also be deteriorated. The average total pressure has a trend of markedly increasing at the outlet of rotor; Reversed flow will happen in blade pressure side when installation angle is smaller in off-design condition and the smaller the installation angle, the larger the reverse flow area. Volume flow rate, pressure and torque of fan present an increasing tendency in various degrees with increasing of installation angle, and the fan total efficiency increases at first and then decrease. The total efficiency reduces 3.77% with total pressure drops 23.7% under the decreasing installation angle of 11°, and the peak value arrived at design angle of installation.
This paper describes the shape optimization of a stator blade in a single-stage transonic axial compressor. The blade optimization has been performed using response surface method and three-dimensional Navier-Stokes analysis. Two shape variables of the stator blade, which are used to define a stacking line, are introduced to increase an adiabatic efficiency. Data points for response evaluations have been selected by D-optimal design, and linear programming method has been used for an optimization on a response surface. Throughout the shape optimization of a stator blade, the adiabatic efficiency is increased to 5.8 percent compared to that of the reference shape of the stator. The increase of the efficiency is mainly caused by the pressure enhancement in the stator blade. Flow separation on the blade suction surface of the stator is also improved by optimizing the stator blade. It is noted that the optimization of the stator blade is also useful method to increase the adiabatic efficiency in the axial compressor as well as the optimization of a rotor blade, which is widely used now.
Numerical optimization for design of a blade stacking line of a low speed axial flow fan with a fast and elitist No Dominated Sorting of Genetic Algorithm (NSGA-II) of multi-objective optimization using three-dimensional Navi Stokes'dnalysis is presented in this work. Reynolds-averaged Navier-stokes (RANS) equations with k-e turbulen model are discretized with finite volume approximations and solved on unstructured grids. Regression analysis is p formed to get second order polynomial response which is used to generate Pareto optimal front with help of NSGA and local search stratery with weighted sum approach to refine the result obtained by NSGA-II to get better Par opimal front. Four geomefric variables related to spanwise distributions of sweep and lean of blade stacking line chosen as design variables to find higher performed fan blade. The performance is measured in terms of the objectiv total effieiency, total pressure and torque. Hence the motive of the optimization is to enhance total efficiency and to pressureland to reduce torque.
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