Rotor Blade Shape Research Articles

Modal Parameter Identification and Damage Localization of Composite Helicopter Rotor Blades Based on AR/PR Identification

The structural characteristics and application background of helicopters determine that the primary dynamic components work in environments with high cyclic amplitude and low‐stress vibration fatigue load. As the most critical structural system of helicopters, structural health monitoring of the rotor blades is necessary to avoid fatigue damage under working conditions. Modal parameters, as functions of the physical properties of structural systems, change when there is damage or internal defects (the mass, stiffness, and damping of the structure will change). This article completes the identification of modal parameters of composite rotor blades under working conditions based on operational modal analysis (OMA). Specifically, using the AR/PR (autoregressive/polyreference) time‐domain identification method, experiments are designed to identify the modal parameters (natural frequency, modal damping ratio, and mode shape) of composite rotor blades based on acceleration and strain signals. The results of the identification of modal parameters are verified through finite element simulation and modal measurement experiments. In addition, the application of OMA for the location of composite rotor blade damage is also studied.

Experimental Study on Airflow Upwash and Control of Thrust Increase Induced by Ceiling Effect on Microrotor

Abstract This study examines the mechanism of thrust increase due to the ceiling effect in near-ceiling flight, which is one of the concerns for the practical application of micro-air vehicles in indoor environments. We also proposed a novel rotor blade shape with a pressure recovery hole as one of the passive control techniques and investigated its effectiveness in controlling the thrust increase. The obtained results showed a rapid thrust increase, with an outward swirling flow between the rotor blade and ceiling, observed with a rectangular blade with an extremely small distance between the upper surface of the rotor blade and ceiling. The rapid thrust increase was caused by a pressure difference between the rotor blade and the lower surface of the ceiling in addition to the rotor blade rotation, which generated an outward swirling flow between the rotor blade and ceiling. In addition to the force generated by the pressure difference between the upper and lower blade surfaces due to their rotation, the negative pressure area created by the rotor blades generates the airflow upwash. For the thrust-control rotor blade, the ratio of the pressure recovery hole to the rotor blade radius was 0.5, which maintained approximately 90% or more of the thrust without the upper wall of the rectangular blade; moreover, the distance between the ceiling and the rotor blade at which the thrust began to increase rapidly became shorter, flight performance was generally maintained in the absence of the ceiling, and the thrust increase amplitude was suppressed.

Dissipated energy and efficiency as objective functions for the design of the NeoVAD rotary blood pump.

Minimising haemolytic blood damage is an important objective when designing rotary blood pumps, however, calculating haemolysis can be computationally expensive and inaccurate. Efficiency and dissipated energy are much more easily calculable hydraulic parameters in the design and analysis of rotary blood pumps and although there is work to suggest that efficiency is not a good indicator of haemocompatibility, i.e. more efficient pumps do not necessarily cause less damage, there is recent speculation that dissipated energy can act as an easily calculable haemolysis analogue.This study shows that for design purposes, optimising for maximum efficiency and minimum dissipated energy are functionally the same as they are inherently and closely linked. Moreover a demonstration of rotary blood pump design has been completed using the NeoVAD paediatric left ventricular assist device optimising for both objective functions. The resulting designs appear similar in rotor blade shape and are similar in hydraulic performance.Clinical relevance- This reinforces the direct link between efficiency and dissipated energy when analysing rotary blood pumps at a given design operating point. This raises questions either of the claim that efficiency cannot be used as an easily calculable analogue for haemolysis or the validity of dissipated energy to act in this same manner.

Optimal Design and Analysis of a High-Load Supersonic Compressor Based on a Surrogate Model

To explore the internal flow mechanism and improve the performance of a supersonic compressor, an efficient global optimization design method was developed for an axial flow compressor and applied in the optimization design of a prototype supersonic compressor. Based on the multiple circular arc (MCA) blade parameters, the method can be used to parameterize the elementary stage of the blade. The optimized solution is obtained by changing the elementary stage and stacking lines of the blade during the optimization process. It has the advantages of fewer optimization variables, strong physical intuition, and a smooth surface. The optimization results show that a change in the rotor blade shape parameters has a significant effect on the compressor efficiency under design conditions, while a change in the skewed-swept parameters of the stator is the main factor that improves the compressor’s performance under near-stall conditions. Further numerical results show that the optimized rotor changes the form of the shock, weakens the degree of shock boundary layer interference, inhibits the radial migration flow of the supersonic rotor, reduces the loss of the rotor blade top, and improves the performance of the compressor under design conditions. The stator’s optimization restrains the generation of a concentrated shedding vortex at the root of the blades and greatly improves the stall margin of the compressor. Finally, the total pressure ratio and flow rate are less than 1% of the values based on the prototype operating conditions, the design mass flow of the optimized high-load supersonic compressor is increased by 0.25%, the isentropic efficiency is increased by 1.05%, and the stall margin is enhanced by 3.5%, thus verifying the effectiveness of the optimization method.

Influence of the shape of the cross-section of the blades on the pumping characteristics of a turbomolecular vacuum pump

The influence of the shape of the cross-section of the blades of a turbomolecular vacuum pump on its main characteristics in the mode of free molecular gas flow is considered. The possibility of a significant increase in the maximum ratio of pump pressures by modifying the cross-sectional shape of rotor and stator blades is shown. Keywords: turbomolecular vacuum pump, blade cross-sectional shape, Monte Carlo method, maximum speed of action, maximum pressure ratio. fominaim@bmstu.ru

Numerical investigation on the hovering performance of contra-rotating ducted rotor for micro air vehicle

In this study, the hovering performance of contra rotating ducted rotor (CRDR) for micro air vehicle (MAV) was performed by using computational fluid dynamics technique. A rotor shape with 5-inch diameter and 4.3-inch pitch for MAV was used. Aerodynamic performance and flow structures were investigated for a single rotor (SR), Contra Rotating Open Rotor and CRDR at various operating RPMs. In case of CRDR, thrust increased by 170% compared to that of SR due to the acceleration of flow at the duct inlet, and approximately 20% thrust improvement was observed compared to CROR. Duct of the CRDR was found to produce approximately 30% of the total thrust. Because torque of rear rotor is slightly greater than that of front rotor, adjustment of RPM or rotor blade shape would be necessary for the torque cancellation. Efficiency of each system was compared based on the power loading, and it was found that CRDR configuration is the most efficient configuration to generate thrust by consuming minimum power.

Coupled aerostructural shape and topology optimization of horizontal-axis wind turbine rotor blades

Traditionally, Aerodynamic Shape Optimization (ASO) and Structural Topology Optimization (STO) are considered as two separate, consecutive stages in the aerostructural design process of wind turbine rotor blades. Since such a modeling strategy does not adequately account for the coupling effects between the blade aerodynamics and its structural performance, in this paper a Coupled Multi-objective Shape and Topology Optimization (CMSTO) approach is presented, which simultaneously optimizes the outer shape and the interior structural layout of the turbine blade from aerodynamic and structural requirements. The framework uses the weighted sum method, whereby the sum of the aerodynamic and structural objectives multiplied by specific weighting factors is minimized employing an incremental-iterative update procedure. The coupled optimization process is performed by sequentially carrying out shape and topology optimization steps for beam-type structures, in accordance with a staggered scheme. For the aerodynamic and structural optimizations the rotor power coefficient and the blade structural compliance are considered as the objectives, respectively. The aerodynamic response of the blade is evaluated by the Blade Element Momentum (BEM) method, which, together with a reduced beam-type Finite Element Method (FEM) model that simulates the structural response, facilitates the application of a gradient-based algorithm with analytical sensitivities. Accordingly, the computational efficiency of the CMSTO framework is warranted. The shape design variables are characterized by the locations of Non-Uniform Rational B-Splines (NURBS) control points that parameterize the blade outer shape. The topology design variables are represented by the relative densities assigned to the finite elements modeling the blade cross-sections, in correspondence with the Simplified Isotropic Material with Penalization (SIMP) method. The CMSTO framework is used to optimize the NREL 5 MW reference rotor blade, whereby the results are compared to those obtained from a separate ASO-STO approach and a pure STO approach. The rotor power coefficients calculated by the CMSTO and ASO-STO approaches are about 4% larger than that of the reference rotor blade. In addition, the blade structural compliance computed by the CMSTO approach is reduced by an extra 16% and 41% compared to the compliances found by ASO-STO and pure STO approaches, respectively. Such significant improvements clearly demonstrate the benefits of the CMSTO approach in the quest of wind turbines with higher power output and better structural performance.

Rotor blade aerodynamic shape optimization based on high-efficient optimization method

In order to design a high-performance rotor, a high-efficient optimization method is established by coupling Kriging model and sequential quadratic programming with high-accuracy computational fluid dynamics method. In order to obtain the global optimal design point, the initial blade shape is optimized by using the Kriging model coupled with genetic algorithm based on the baseline rotor blade (Helishape 7A rotor). After that, the modified sequential quadratic programming method is employed to search the final blade shape based on the initial blade shape deeply. In the optimal process, the regions of design variables are restricted considering rotor dynamic characteristics. As a result, a new shape of rotor blade with characters of nonlinear twist, variational chord length, complex swept, and anhedral distributions is obtained. Compared with the baseline rotor, blade-tip vortex of the final optimized rotor is significantly weakened, the figure of merit of the final optimized rotor increases about 3.42%, and the peak of sound pressure decreases about 16.9%. At the same time, it is demonstrated that the final optimized rotor has better forward flight characteristics.

Performance improvement of helicopter rotors through blade redesigning

Purpose The purpose of this paper is to determine dependencies between a rotor-blade shape and a rotor performance as well as to search for optimal shapes of blades dedicated for helicopter main and tail rotors. Design/methodology/approach The research is conducted based on computational methodology, using the parametric-design approach. The developed parametric model takes into account several typical blade-shape parameters. The rotor aerodynamic characteristics are evaluated using the unsteady Reynolds-averaged Navier–Stokes solver. Flow effects caused by rotating blades are modelled based on both simplified approach and truly 3D simulations. Findings The computational studies have shown that the helicopter-rotor performance may be significantly improved even through relatively simple aerodynamic redesigning of its blades. The research results confirm high potential of the developed methodology of rotor-blade optimisation. Developed families of helicopter-rotor-blade airfoils are competitive compared to the best airfoils cited in literature. The finally designed rotors, compared to the baselines, for the same driving power, are characterised by 5 and 32% higher thrust, in case of main and tail rotor, respectively. Practical implications The developed and implemented methodology of parametric design and optimisation of helicopter-rotor blades may be used in future studies on performance improvement of rotorcraft rotors. Some of presented results concern the redesigning of main and tail rotors of existing helicopters. These results may be used directly in modernisation processes of these helicopters. Originality/value The presented study is original in relation to the developed methodology of optimisation of helicopter-rotor blades, families of modern helicopter airfoils and innovative solutions in rotor-blade-design area.

Simulation of Swirling Turbulent Flow Aerodynamics in a Centrifugal Machine

This work presents a numerical simulation of the aerodynamics of a swirling turbulent flow in a vortex chamber of a combined pneumatic centrifugal machine with a rotor located in its upper part and consisting of a system of rotating blades. Numerical analysis of the swirling turbulent flow made it possible to determine the main patterns in the behavior of the carrier agent in the machine. As a result, a modification of the rotor blade shape is proposed, which allows the distribution change of the radial velocity field as necessary. Numerical studies have shown the promise of this approach for controlling the radial velocity component in the rotor, which is a necessary condition for the separator to operate efficiently. The conducted numerical calculations are validated using test studies and a comparison with experimental data.

Rotor blade shape reconstruction from strain measurements

Traditional helicopter blades are subject to significant deformations, which influence control forces and moments, as well as the helicopter aeroelastic and aeroacoustic behavior. Thus, the knowledge of rotor elastic states could help improving flight control efficiency, and reducing vibration level and acoustic emissions of next-generation helicopters. This paper presents an original and computationally efficient modal approach aimed at dynamic shape sensing of helicopter rotor blades. It is based on strain measurements in a limited number of points over the blade surface. Although the algorithm is based on the cascaded solution of linear algebraic equations, much like other modal-based algorithms, it is able to reconstruct nonlinear, moderate lag, flap and torsional deflections, which are typical in helicopter structural dynamics. The algorithm is tested on non-rotating and rotating hingeless blades through numerical simulations based upon a multibody dynamics solver for general nonlinear comprehensive aeroelastic analysis. Its capabilities are assessed against those of classical modal approaches. Numerical investigations show that the proposed algorithm is reliable, accurate and robust to measurement noise.

Reconstruction method for running shape of rotor blade considering nonlinear stiffness and loads

The aerodynamic and centrifugal loads acting on the rotating blade make the blade configuration deformed comparing to its shape at rest. Accurate prediction of the running blade configuration plays a significant role in examining and analyzing turbomachinery performance. Considering nonlinear stiffness and loads, a reconstruction method is presented to address transformation of a rotating blade from cold to hot state. When calculating blade deformations, the blade stiffness and load conditions are updated simultaneously as blade shape varies. The reconstruction procedure is iterated till a converged hot blade shape is obtained. This method has been employed to determine the operating blade shapes of a test rotor blade and the Stage 37 rotor blade. The calculated results are compared with the experiments. The results show that the proposed method used for blade operating shape prediction is effective. The studies also show that this method can improve precision of finite element analysis and aerodynamic performance analysis.

Aerodynamic design optimization of helicopter rotor blades including airfoil shape for forward flight

This study proposes a process to obtain an optimal helicopter rotor blade shape including both planform and airfoil shape for helicopter aerodynamic performance in forward flight. An advanced geometry representation algorithm which uses the Class Function/Shape Function Transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape was considered in terms of design variables. The optimization process was constructed by integrating several programs developed by the author. Airfoil characteristics are automatically generated by an analysis tool where lift, drag, and moment coefficients of airfoil are predicted for subsonic to transonic flow and a wide range of attack angles. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight, aerodynamic requirements (lift, drag and moment coefficients) for critical flow condition occurring on rotor blades. The trim condition must be attainable in any flight condition. Objective function is chosen as a combination expression of non-dimensional required power in hover and forward flight.

무인비행체 블레이드 형상 변화에 따른 단일로터의 제자리 비행 추력성능 분석

무인비행체 블레이드 형상 변화에 따른 단일로터의 제자리 비행 추력성능 분석

200 W급 자이로밀형 수직축 풍력터빈 로터 블레이드 형상설계 및 유동해석

This study is focused on the shape design and flow analysis on a 200 W-class Gyromill type vertical axis wind turbine rotor blade. Single tube theory is adopted for the shape design of the turbine blade. 2-dimensional CFD analysis is conducted to examine the turbine performance with basic shape, and then 3-dimensional shape is determined from the examination of the performance. By the CFD analysis on the 3-dimensional shape of the wind turbine, performance of the turbine is examined and also, shape of the wind turbine rotor blade is determined accordingly. From the results of this study, a 200 W-class Gyromill type vertical axis wind turbine rotor blade is designed and the reliability of the design method is confirmed by CFD analysis.

Aerodynamic design optimization of helicopter rotor blades including airfoil shape for hover performance

This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.

English

In this paper the shape of rotor blades in Marine Current Turbines (MCTs) are investigated. The evaluation of hydrodynamic loads on blades is performed based on the Blade Element Momentum (BEM) theory. The shape of blades is optimized according to the main parameters in the configuration and operation of these devices. The optimization is conducted based on the ability of the blades to harness the maximum energy during operating. The main parameters investigated are the tip speed ratio and angle of attack. Furthermore, the influence of these parameters on the maximum energy extraction from fluid flow over a hydrofoil is evaluated. It is shown that the effect of the angle of attack on power extraction is greater than that of the tip speed ratio, while both are found to be significant. Additionally, the proper angle of attack is the angle at which the lift to drag ratio is at its maximum value. However, if a proper angle of attack is chosen, the variations in power coefficient would not be effectively changed with small variations in the tip speed ratio.

Aerodynamic shape optimization of hovering rotor blades using a coupled free wake–CFD and adjoint method

This paper concerns a numerical optimization method for designing helicopter rotor blades in hover based on adjoint method and by using a coupled free wake–CFD approach for proper calculation of aerodynamic loads. The Euler flow solver and adjoint equations are formulated in a rotating coordinate system. The rotor wake effects are modeled by a free wake method and included into the CFD calculation. The approach is applied for the redesign of a transonic Caradonna–Tung two-bladed rotor through minor surface changes. The inviscid torque was reduced about 15% from that of original rotor due the reduction of wave drag. Results show that this technique is capable of converging to the optimum aerodynamic shape of rotor blades with minimum inviscid rotor torque coefficient under fixed thrust constraint. The advantage of this method is that satisfactory results can be achieved by minimum computational efforts, particularly for the grid generation problem and the required CPU time.

0908 最適化手法を用いた風レンズ風車の空力設計(OS9 再生可能流体エネルギーの利用技術,オーガナイズドセッション)

An aerodynamic optimal design method for wind-lens turbine using the Genetic Algorithm has been developed.In the present method,the aerodynamic design for the wind-lens turbine rotor is based on an axisymmetnc viscous flow analysis and a two-dimensional blade element design.The present optimal design method is able to search for the optimal wind-lens and rotor blade shape simultaneously.This coupled design method of turbine rotor and wind-lens has achieved to generate high performance wind-lens turbines.Three-dimensional Reynolds averaged Navier-Stokes(RANS) simulation shows that the new wind-lens turbine designed by the genetic algorithm design method is superior to conventional one in the total performance.

Optimisation of aspects of rotor blades in forward flight

This work presents a method for the optimisation of aspects of rotor blade shape in forward flight. The proposed technique employs CFD in conjunction with artificial neural networks (ANNs) and genetic algorithms (GAs). The developed method was used to optimise the anhedral and sweep of the UH60-A rotor blade in forward flight. A parameterisation method was defined, a specific objective function was created using the initial CFD data and the metamodel was used for evaluating the objective function during the optimisation. The obtained results suggest optima in agreement with engineering intuition but provide precise information about the shape of the final lifting surface and its performance. The results were checked using different optimisation methods and metamodels and were not sensitive to the employed techniques with substantial overlap between the outputs of the selected methods. The main CPU cost was associated with populating the CFD database necessary for the metamodel.