Aerodynamic Blade Research Articles

Effect of Multistage Circulation Control on Blade Aerodynamic Performance

Effect of Multistage Circulation Control on Blade Aerodynamic Performance

Stochastic aerodynamic analysis for compressor blades with manufacturing variability based on a mathematical dimensionality reduction method

It is essential for engineering manufacture and robust design to evaluate the impact of manufacturing variability on the aerodynamics of compressor blades efficiently and accurately. In the paper, a novel quadratic curve approximation method based on the scanning points of blade design profiles was introduced and combined with Karhunen–Loève expansion, a mathematical dimensionality reduction method for modeling manufacturing variability as truncated Normal process was proposed. Subsequently, Sparse Approximation of Moment-based Arbitrary Polynomial Chaos (SAMBA PC) and computational fluid dynamics (CFD) were applied to build a computational framework for stochastic aerodynamic analysis considering manufacturing variability. Finally, the framework was adopted to evaluate the aerodynamic variations of a high subsonic compressor cascade under the design incidence. The results illustrate that the SAMBA PC method is more efficient than the traditional methods such as Monte Carlo simulation (MCS) for stochastic aerodynamic analysis. Through uncertainty quantification, the impact of manufacturing variability on the global aerodynamic performance is primarily reflected in the fluctuation of aerodynamic losses, and the fluctuation of the total losses is mainly contributed by the fluctuation of the separation loss after the suction peak (a negative pressure spike near the leading edge (LE)) and the boundary-layer loss on the suction surface (SS). With sensitivity analysis, the most important geometric modes to aerodynamics can be revealed, which provides a useful reference for manufacturing inspection process and helps reduce computational cost in robust design.

Aerodynamic Analysis of Micro Aerial Vehicle Rotor Blade at Low Reynolds Number

The numerical simulation of micro aerial vehicle (MAV) rotor blade aerodynamics is highly challenging in the field of rotor aerodynamics. The aim of this paper is to present a computational fluid dynamics (CFD) study on the aerodynamics analysis of micro aerial vehicle rotor blade at low-Reynolds number by means of Spalart-Allmaras turbulence model. The KA152313 airfoil, which is dedicated to mid to small-scale rotorcraft, e.g. MAV is chosen to design the rotor blade. The rotor blade was investigated in three different pitch configurations, which are GP13º, GP12º and GP11º and the aerodynamics characteristics are analyzed respectively. The CFD results of the analysis is used to compare the aerodynamic characteristics, e.g. pressure force, shear force and pitching moment on the chord surface of the rotor blades at different pitch configurations.

Evaluation of operational strategies on wind turbine power production during short icing events

Cold climates around the world are seeing increasing investment in wind power generation. The benefits of cold regions, however, come with unique challenges such as the accumulation of ice on wind turbine blades, which impacts the aerodynamic properties of the blades and, in turn, power production. One decision that must be made when facing an icing event is whether to maintain operation of the turbine or to pause the rotor until the event has passed. Powering through an icing event allows the operator to maintain power production, but with an increase in ice accumulation and associated adverse effects. Pausing the wind turbine results in less ice accumulation and may therefore provide higher power production once operation is resumed. The aim of this research was to complete a comparative assessment of these two strategies with regards to overall impact on power production. A numerical Ice and Power Model was developed, validated, and employed to assess power production impacts on a 1.5 MW wind turbine for five 2-h icing events with varying atmospheric parameters. The simulation results on short icing events provide evidence that while pausing the turbines does indeed result in significantly less ice accumulation, the positive impact on power production compared to the power-through strategy is insufficient to justify the shut-down strategy. This is found to be due to the overpowering impact of surface roughness from ice crystal beading on blade aerodynamics, which occurs whether or not the blades are rotating.

Comparison of neural network types and architectures for generating a surrogate aerodynamic wind turbine blade model

Current numerical aerodynamic wind turbine blade models – models that calculate the aerodynamic loads on a blade based on the incoming wind – are generally computationally intensive. However, a surrogate aerodynamic blade model consisting of a neural network (NN) trained on high-accuracy data should be capable of achieving both high accuracy and fast computation times. In this study, six different NNs were trained using numerical data from aeroelastic blade simulations, then compared for the highest possible prediction accuracy while maintaining high speeds. The NNs include two time-independent multilayer perceptron (MLP) networks with a full and reduced set of input data. A time-dependent long short-term memory (LSTM) network was also trained, along with a similar Pseudo-time-dependent MLP. Finally, a time-dependent convolutional neural network (CNN) and a similar Multi-time-step MLP were trained and compared. Over 30 million data points of aeroelastic time history information of an operational 5MW wind turbine across 115 time histories and 23 different mean wind speeds were numerically generated for training the networks. The architecture, input and output data, and the optimization and training processes are provided in detail for each network, and the resulting accuracy and computation times are analyzed and compared. Ultimately, it was found that both the trained full-input MLP and the CNN were particularly accurate surrogate models, with average normalized root mean square errors of 1.11% and 0.66% respectively. While the CNN surpasses the full-input MLP in accuracy, the latter is simpler to train and faster to run, thus both are compelling options for future researchers. Such a surrogate model could be used to predict the aerodynamic loads on a wind turbine blade when computation speed is a priority, such as during design optimization or hybrid simulations.

Horizontal axis wind turbines passive flow control methods: a review

In improving wind turbine torque and power output, the aerodynamic characteristics of wind turbines blades play an important role. Unleashing easy but efficient flow enhancement techniques over aerofoil sections used in horizontal axis wind turbines (HAWT) has become essential in the increasing demand for this source of renewable energy. These techniques or methods are primarily categorized into two kinds: active and passive. Active methods of flow control need energy expensewhereas passive flow control methods are needless of auxiliarypower. This paper investigates various passive flow control strategies that have great potential to boost the aerodynamics of blades of HAWT. The mechanisms and working principles, along with the findings from various experimental studies and CFD results for passive flow control systems are included in this article. Also, some of these studies are supported by demonstrating the lift and coefficient of drag (CD) variation with the angle of attack (AoA). The review suggests simple, cost-effective ways of improving lift and controlling the aerofoil stalling behaviors to obtain higher power efficiency for HAWT.

OPTIMIZATION OF FLOATING HORIZONTAL AXIS WIND TURBINE (FHAWT) BLADES FOR AERODYNAMIC PERFORMANCE MEASUREMENT

Wind power is one of the most important sources of renewable energy which extract kinetic energy from the wind. Currently much research has concentrated on improving the aerodynamic performance of wind turbine blade through wind tunnel testing and theoretical studies. However, wind turbine simulation through Computational Fluid Dynamics (CFD) software offers inexpensive solutions to aerodynamic blade analysis problem. The purpose of this paper is to find the effect of angle of attack towards the blade of Floating Horizontal Axis Wind Turbine (FHAWT) and optimize to get the best blade performance in between twisted and untwisted blade which will give maximum lift and drag force ratio. The optimization of the FHAWT blades are carried out by analysing, modelling and simulation by using simplified spreadsheet method, CFD analysis in ANSYS WORKBENCH 2020 R1 software and wind tunnel testing. The blades are evaluated regarding their lift and drag force ratio in different angle of attack and wind speed. The results, obtained from both computer programs, wind tunnel testing and the initial hand calculations, are comparable and satisfying. Finally, the model was implemented to optimize blades performance, especially at low wind velocities, which is crucial to produce power during operating in offshore environment.

Effect of low-level jet on turbine aerodynamic blade loading using large-eddy simulations

Low-level jets (LLJs) are winds with high-shear and large wind energy potential. We perform large-eddy simulations (LES) with actuator line modeling of a turbine operating in a moderately stable boundary layer in the presence of LLJs. We find that the turbine tip and root vortices break down quickly when the LLJ is above the turbine rotor swept area. In contrast, the wake recovery is slow, and the vortices are stable when the LLJ is in the middle or even below the rotor swept area. The LLJ shear causes significant azimuthal variation in the external aerodynamic blade loading, increasing fatigue loading on the turbines. We observe that both tangential and axial forces on the blades are highest when the blade directly interacts with the LLJ. Azimuthal variation in the tangential forces on the blades is the highest when the LLJ is above the rotor swept area, i.e. when the turbine operates in the positive shear region of LLJ, with the blade tip interacting with the LLJ.

Structural optimization of H-type VAWT blade under fluid-structure interaction conditions

To reduce the errors caused by the rigid body hypothesis in the aerodynamics-structure coupling calculation and improve the structural performance, an optimum structure design with the consideration of the fluid-structure interaction are performed for the H-type vertical axis wind turbine (VAWT) blade. Based on the ANSYS Workbench platform, the geometric model, computational domain and grids of the wind wheel are constructed, the turbulence model, boundary conditions and composite material layers are set up, and the fluid and solid domains are solved in a coupled way. The single-objective structural optimization model in which the thicknesses of glass clothes, foam and gel coat, and the positions of two webs are taken as design variables is solved using the response surface optimization method to minimize the wind wheel mass. The frequencies and vibration modes of original and optimized blades with and without pre-stress and the transient characteristics of wind wheels in different wind speeds are investigated. The results indicate that after the blade optimization, the first-order frequency and critical speed become larger and other frequencies reduce for the static, single pre-stress and multiple pre-stresses states, and the maximum displacement, stress and strain of the wind wheel decrease under rated and extreme wind speeds, confirming significant performance improvements. The research provides useful guidance for the integrated design of structure and aerodynamics of wind turbine blades.

Numerical Study on the Aerodynamic Characteristics of the NACA 0018 Airfoil at Low Reynolds Number for Darrieus Wind Turbines Using the Transition SST Model

A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model.

The effects of winglet on hawt blade and the optimum ratio between wing and winglet dimensions

Government wanted to make India a leading wind power nation. The government offers SOP to private investors to setup wind farms. But the wind flow patterns and the nature of the terrain are not always support to the installation of wind farms. Many stations have little wind to run their windmills. Even if power is generated, companies do not find it profitable to sell to the grid. Induced drag developed by tip vortices stands as a major reason for low power output. This study aims to find the changes in the power generation by wind mills after the addition of winglet to wind turbine blade and also to find an optimum ratio between the span of wing and winglet. The winglet helps to reduce the induced drag. A horizontal axis wind turbine (HWAT) with winglets is proposed. The selection of different airfoil shapes from NACA series was done and blade aerodynamics was simulated to investigate the flow structures and general aerodynamic coefficients are extracted using ANSYS software. A comparison of aerodynamic performance of different airfoil geometries is done to find a suitable airfoil shape based on L/D characteristics. 3D model analysis of blade from selected airfoil cross section, with and without winglet is carried out using ANSYS Fluent and the aerodynamic performance is compared to study the effectiveness of the winglet. It is found that the blade with winglet gives an L/D ratio of 13.8 compared to the one without winglet, 8.8, for a 3m wing span. The study then continued with the wing span of 5m and 7m. The study also extends to find an optimum ratio between wing and winglet.

Aerodynamic study for the flow through cascade blades of gas turbine with vibration effect: a review

A research survey on aerodynamic with/without vibration effect and investigations for turbine components of gas turbine engines is presented. Experimental and numerically predicted results are presented from investigations undertaken over the past 70 years. The aerodynamics between the turbine blades is very important as it determines the overall system performance. The importance of aerodynamics is being in the pressure distribution above and below each airfoil, the locations of the vortices occurring, their number, distribution, direction, and shedding, and the determination of the regions of fluid separation from the wall that is directly related to the fluid velocity. Many ranges of vibration that affect different bodies were taken, and some of these ranges were small (10-200 Hz), and others had large ranges from 1.5 to 10 KHz. therefore the result evolution and shedding of vortices corresponding to the deformation in fluid structure depends on the Reynolds number and value of amplitude and frequency for vibration. The Mach number is a clear indicator to represent these characteristics. It also includes studying the theoretical methods used and simulations of the researchers’ aerodynamics, the accuracy of the results reached, the representation of the body contour and the diagrams for each of the pressure and Mach number, the pressure (Cp ) and lift (CL ) coefficients, and their amount of change occurring at each location of the airfoil. The importance of the above topics has motivated us to prepare a comprehensive review mostly of the aerodynamics of turbine blades and the effect of the vibration on the flow. The main concepts of aerodynamics, such as Cp and CL as well as vibration frequency are presented. It also highlights the performance of the turbine blades as a result of vibration

Effect of Ice accretion on the aerodynamic characteristics of wind turbine blades

Cold regions with high air density and wind speed attract wind energy producers across the globe exhibiting its potential for wind exploitation. However, exposure of wind turbine blades to such cold conditions bring about devastating impacts like aerodynamic degradation, production loss and blade failures etc. A series of wind tunnel tests were performed to investigate the effect of icing on the aerodynamic properties of wind turbine blades. A baseline clean wing configuration along with four different ice accretion geometries were considered in this study. Aerodynamic force coefficients were obtained from the surface pressure measurements made over the test model using MPS4264 Simultaneous pressure scanner. 3D printed Ice templates featuring different ice geometries based on Icing Research Tunnel data is utilized. Aerodynamic characteristics of both the clean wing configuration and Ice accreted geometries were analysed over a wide range of angles of attack (α) ranging from 0° to 24° with an increment of 3° for three different Reynolds number in the order of 105. Results show a decrease in aerodynamic characteristics of the iced aerofoil when compared against the baseline clean wing configuration. The key flow field features such as point of separation, reattachment and formation of Laminar Separation Bubble (LSB) for different icing geometries and its influence on the aerodynamic characteristics are addressed. Additionally, attempts were made to understand the influence of Reynolds number on the iced-aerofoil aerodynamics.

Study on the Intelligent Modeling of the Blade Aerodynamic Force in Compressors Based on Machine Learning

In order to obtain the aerodynamic loads of the vibrating blades efficiently, the eXterme Gradient Boosting (XGBoost) algorithm in machine learning was adopted to establish a three-dimensional unsteady aerodynamic force reduction model. First, the database for the unsteady aerodynamic response during the blade vibration was acquired through the numerical simulation of flow field. Then the obtained data set was trained by the XGBoost algorithm to set up the intelligent model of unsteady aerodynamic force for the three-dimensional blade. Afterwards, the aerodynamic load could be gained at any spatial location during blade vibration. To evaluate and verify the reliability of the intelligent model for the blade aerodynamic load, the prediction results of the machine learning model were compared with the results of Computation Fluid Dynamics (CFD). The determination coefficient R2 and the Root Mean Square Error (RMSE) were introduced as the model evaluation indicators. The results show that the prediction results based on the machine learning model are in good agreement with the CFD results, and the calculation efficiency is significantly improved. The results also indicate that the aerodynamic intelligent model based on the machine learning method is worthy of further study in evaluating the blade vibration stability.

Employing Computational Fluid Dynamics to Derive Beddoes–Leishman Model Airfoil Parameters for Vertical Axis Wind Turbines

AbstractThe blades of a vertical axis wind turbine (VAWT) experience large variations in the angle of attack at low tip-speed ratios and induce blade force oscillation. These unsteady aerodynamic effects must be considered in the VAWT aerodynamic modelling methodology by utilizing a dynamic stall model. The Beddoes–Leishman (B–L) dynamic stall model is a popular method to simulate the unsteady VAWT blade dynamic stall aerodynamics. However, a limitation of the B–L dynamic stall model is the number of the airfoil dependent parameters derived from both steady and unsteady experimental measurements. In this paper, a methodology is described to compute these B–L dynamic stall model airfoil coefficients utilizing a computational fluid dynamics (CFD) model. This method permits the calculation of the blade dynamic stall characteristics over a range of reduced pitch rates by employing a user-defined sliding mesh motion technique. Furthermore, the variation in the blade Reynolds number is accounted for by conducting simulations at the maximum and minimum VAWT envelope operating limits. Aerodynamic blade force experimental measurements are used to compare the predictions from a low-order model with airfoil data extracted CFD and experiments. This approach expands the applicability of the B–L dynamic stall model for large-scale VAWTs.

Load distribution method in helicopter blade multibody dynamics system

The paper focuses on the loads applied to the helicopter blade cross-sections in the multibody dynamics system. The main objective is to simplify the blade aerodynamics calculation and avoid time-consuming CFD methods. For this reason, the way of computing blade aerodynamics is proposed by using multibody dynamics methods with a linear-elastic blade model. As the primary tool for further research, the MCS Adams software package is selected. Splitting the main rotor blade into a finite number of sections, each having its own average value of installation and coning angles, simplifies the calculation. Afterward, expressions for the total flow velocity around the blade section and its angle of attack are obtained through vector operations. This provides a measure of aerodynamic forces acting on each section in its cross-sectional coordinate system. In conclusion, the article provides the formalized method of aerodynamic force distribution between blade sections in the multibody model as well as the correlation between the flow coordinate system and the blade chord coordinate system.

Modeling and Parameter Identification of a Cooling Fan for Online Monitoring

In many industrial fields, cooling fan systems have been widely implemented in electronic equipment such as network hosts, product line junction boxes, manufacturing facilities, computer numerical control (CNC) machine systems, cooling units of array servers, and many other power systems. These systems usually require high computation power and release high heat. Once the cooling fan systems malfunction or the cooling efficiency degrades, it could result in lower system performances or even cause serious damage to the core systems. Thus, there is a growing interest in monitoring and detecting the cooling fan operation status. As a result, the status of the cooling fan systems needs to be monitored in real-time. In this article, dynamics modeling, parameter identification, and online fan speed monitoring of a cooling fan system are presented. First, the nonlinear model of the cooling fan system is derived from blade aerodynamics with a driving motor. Next, a discrete model is applied based on the bilinear transformation of the description of the dynamic behavior and is further used for the least-square (LS) parameter estimation. To suppress the measurement noise, a regulation filter (RF) is further presented to improve the parameter identification precision. In addition, a Levenberg–Marquardt (LM) optimization is further applied for parameter refinement. Simulation comparison studies are considered to validate the proposed method. Moreover, many experiments are conducted to verify the feasibility and reliability for different types of fans. Unlike common conventional monitoring methods, the proposed framework does not apply constant threshold or need any training stages. The alarm threshold is adjusted automatically according to the current operation status. Finally, an embedded measurement and monitoring instrument is developed for demonstrating the effectiveness of the proposed method. Experiments firmly verify the novelty of the model-reference-based online cooling fan monitoring techniques.

A Coupled Effect Model of Two-Position Local Geometric Deviations on Subsonic Blade Aerodynamic Performance

The coupled aerodynamic performance influence of multiple deviations in the blade profile is a complex phenomena. In this paper, a high-pressure compressor rotor blade mid-span profile is studied with the design of experiments (DOE), numerical simulation and surrogate model to analyze the influence of the deviations on the blade aerodynamic performance. The purpose of this work is to provide a new rapid evaluation approach for the blade aerodynamic performance under multiple geometric deviations influence. First, the Hicks-Henne function was used to model the local geometric deviations of the blade profile, and the blade aerodynamic performance was calculated by using the computational fluid dynamics tools. By analyzing the calculation results, the momentum thickness of the boundary layer, the deviations height and the distance between the deviations are combined into a coupled effect model. Then, the coupled effect model was used to rapidly evaluate the blade aerodynamic performance when the two-position local geometric deviations exist on the blade surface. Finally, the evaluated performance were compared with the results predicted by a high-precision surrogate model, which verifies the high accuracy of the coupled effect model in evaluating the positive incidence range of the blade profile.

Multi-disciplinary optimization of variable rotor speed and active blade twist rotorcraft: Trade-off between noise and emissions

The concepts of variable rotor speed and active blade twist are emerging technologies for the next generation of civil rotorcraft. Previous research has focused on the optimum implementation of these technologies for improved fuel economy and environmental impact. Within this work, an integrated approach is deployed to quantify the concurrent reductions in rotor noise and NOx emissions. A relaxation-based free-wake inflow model, coupled with unsteady blade aerodynamics modeling, resolves the flow-field around the main rotor. Aero-acoustic predictions are performed through an acoustic-analogy-based formulation. Gaseous emissions are then predicted via stirred-reactor modeling, coupled with zero-dimensional engine performance analysis method. This strategy is incorporated into a multi-disciplinary genetic algorithm optimization process based on surrogate modeling. Optimal schedules of combined variable rotor speed and active blade twist controls are derived for a twin-engine light helicopter in descent. The accrued schedules suggest NOx reductions between 6% and 21%, simultaneously with source-noise reductions of the order of 2–8 dB, relative to the non-morphing rotor case. The developed strategy constitutes an enabling methodology for the holistic and multi-disciplinary assessment of morphing helicopter rotor configurations.

Adjoint based optimisation for efficient VAWT blade aerodynamics using CFD

The objective of this work is to demonstrate the viability of applying Adjoint methods to aerodynamic optimisation of VAWTs. Adjoint methods are very powerful optimisation techniques which have been implemented effectively in other fields, yet there is an absence of such work within VAWT literature.A ‘semi-transient’ optimisation process is proposed, using Adjoint optimisation data from single instances in time to improve VAWT performance. This is challenging due to the unsteady nature of VAWT aerodynamics. A pitching aerofoil model approximates the VAWT flow field, drastically reducing computational cost. Details are given on the necessary CFD model(s), Adjoint solver settings, and optimisation philosophy.The optimisation process was applied to a typical VAWT in the commercial CFD software ANSYS Fluent. A high tip-speed-ratio case is chosen to minimise unsteady flow affects. The results show novel blade geometries which improve the VAWT average power coefficient when compared to the original NACA0018 blade.Such a method is novel in the field of VAWTs, and the use of Adjoint methods with low cost CFD models provides an efficient optimisation methodology that can be readily adopted by the VAWT design community. This work sets the foundation for a new and very promising avenue for VAWT research.