Some recent applications of the suction analogy to asymmetric flow situations

A recent extension of the suction analogy for the estimation of vortex loads on asymmetric configurations was reviewed. This includes the asymmetric augmented vortex lift and the forward sweep effect on side edge suction. Application of this extension to a series of skewed wings has resulted in an improved estimating capability for a wide range of asymmetric flow situations. Hence, the suction analogy concept now has more general applicability for subsonic lifting surface analysis

Effects of yawed inflow on the aerodynamic and aeroacoustic performance of ducted wind turbines

Ducted Wind Turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform inflows might be the cause of aerodynamic and acoustic performance degradation. For this reason, an aerodynamic and aero-acoustic analysis of DWTs in yawed inflow condition is performed for two duct geometries: a baseline commercial DWT model, DonQi®, and one with a duct having a higher cross-section camber with respect to the baseline, named DonQi D5. The latter has been obtained from a previous optimization study. A numerical investigation using Lattice-Boltzmann Very-Large-Eddy Simulations is presented. Data confirm that the aerodynamic performance improvement, i.e. increase of the power coefficient, is proportional to the increase of the duct thrust force coefficient. It is found that, placing the DWT at a yaw angle of 7.5 , the aerodynamic performances of the DonQi D5 DWT model are less affected by the yaw angle. On the other hand, this configuration shows an increase of broadband noise with respect to the baseline DonQi® one, both in non-yawed and yawed inflow conditions. This is associated to turbulent boundary layer trailing edge noise due to the turbulent flow structures developing along the surface of the duct

Multiaxis thrust vectoring using axisymmetric nozzles and postexit vanes on an F/A-18 configuration vehicle

A ground-based investigation was conducted on an operational system of multiaxis thrust vectoring using postexit vanes around an axisymmetric nozzle. This thrust vectoring system will be tested on the NASA F/A-18 High Alpha Research Vehicle (HARV) aircraft. The system provides thrust vectoring capability in both pitch and yaw. Ground based data were gathered from two separate tests at NASA Langley Research Center. The first was a static test in the 16-foot Transonic Tunnel Cold-Jet Facility with a 14.25 percent scale model of the axisymmetric nozzle and the postexit vanes. The second test was conducted in the 30 by 60 foot wind tunnel with a 16 percent F/A-18 complete configuration model. Data from the two sets are being used to develop models of jet plume deflection and thrust loss as a function of vane deflection. In addition, an aerodynamic interaction model based on plume deflection angles will be developed. Results from the scale model nozzle test showed that increased vane deflection caused exhaust plume turning. Aerodynamic interaction effects consisted primarily of favorable interaction of moments and unfavorable interaction of forces caused by the vectored jet plume

Estimation of wind turbine blade aerodynamic performances computed using different numerical approaches

Although much employed, wind energy systems still present an open, contemporary topic of many research studies. Special attention is given to precise aerodynamic modeling performed in the beginning since overall wind turbine performances directly depend on blade aerodynamic performances. Several models different in complexity and computational requirements are still widely used. Most common numerical approaches include: i) momentum balance models, ii) potential flow methods and iii) full computational fluid dynamics solutions. Short explanations, reviews and comparison of the existing computational concepts are presented in the paper. Simpler models are described and implemented while numerous numerical investigations of isolated horizontal-axis wind turbine rotor consisting of three blades have also been performed in ANSYS FLUENT 16.2. Flow field is modeled by Reynolds Averaged Navier Stokes (RANS) equations closed by two different turbulence models. Results including global parameters such as thrust and power coefficients as well as local distributions along the blade obtained by different models are compared to available experimental data. Presented results include fluid flow visualizations in the form of velocity contours, sectional pressure distributions and values of power and thrust force coefficients for a range of operational regimes. Although obtained numerical results vary in accuracy, all presented numerical settings seem to slightly under-or over-estimate the global wind turbine parameters (power and thrust force coefficients). Turbulence can greatly affect the wind turbine aerodynamics and should be modeled with care

Self-organizing fuzzy sliding-mode control for a voice coil motor

[[abstract]]Voice coil motor (VCM) is widely known as its topquality of free friction, low noise, fast transient response and well repeatability. Yet the dynamic characteristic of a VCM is nonlinear and time-varying, thus the model-based conventional controller is difficult to achieve high-precision control performance for a VCM. To attack this problem, a selforganizing fuzzy sliding-mode control (SFSC) system is proposed in this paper. All of the fuzzy rules are online grown and pruned by the structure learning phase and the parameter learning phase is designed to tune the controller parameter in the gradient-descent-learning algorithm. From the experiment results, it shows that the proposed SFSC system can successfully control a VCM with favorable control response with enhanced disturbance rejection performance.[[notice]]補正完畢[[conferencetype]]國際[[conferencedate]]April 9-11[[booktype]]紙本[[iscallforpapers]]Y[[conferencelocation]]Taipei, Taiwa

Numerical investigation of wind turbine and wind farm aerodynamics

A numerical method based on the solution of Reynolds Averaged Navier Stokes equations and actuator disk respresentation of turbine rotor is developed and implemented in the OpenFOAM software suite for aerodynamic analysis of horizontal axis wind turbines (HAWT). The method and the implementation are validated against the 1-D momentum theory, the blade element momentum theory and against experimental data. The model is used for analyzing aerodynamics of a novel dual rotor wind turbine concept and wind farms. Horizontal axis wind turbines suffer from aerodynamic inefficiencies in the blade root region (near the hub) due to several non-aerodynamic constraints (e.g., manufacturing, transportation, cost, etc.). A new dual-rotor wind turbine (DRWT) concept is proposed that aims at mitigating these losses. A DRWT is designed using an existing turbine rotor for the main rotor (Risoe turbine and NREL 5 MW turbine), while the secondary rotor is designed using a high lift to drag ratio airfoil (the DU 96 airfoil from TU Delft). The numerical aerodynamic analysis method developed as a part of this thesis is used to optimize the design. The new DRWT design gives an improvement of about 7% in aerodynamic efficiency over the single rotor turbine. Wind turbines are typically deployed in clusters called wind farms. HAWTs also suffer from aerodynamic losses in a wind farm due to interactions with wind turbine wakes. An interesting mesoscale meteorological phenomenon called surface flow convergence\u27\u27 believed to be caused by wind turbine arrays is investigated using the numerical method developed here. This phenomenon is believed to be caused by the pressure gradient set up by wind turbines operating in close proximity in a farm. A conceptual/hypothetical wind farm simulation validates the hypothesis that a pressure gradient is setup in wind farms due to turbines and that it can cause flow veering of the order of 10 degrees. Simulations of a real wind farm (Story County) are also conducted which give qualitatively correct flow direction change, however quantitative agreement with data is only moderately acceptable

The NASA-LeRC wind turbine sound prediction code

Since regular operation of the DOE/NASA MOD-1 wind turbine began in October 1979 about 10 nearby households have complained of noise from the machine. Development of the NASA-LeRC with turbine sound prediction code began in May 1980 as part of an effort to understand and reduce the noise generated by MOD-1. Tone sound levels predicted with this code are in generally good agreement with measured data taken in the vicinity MOD-1 wind turbine (less than 2 rotor diameters). Comparison in the far field indicates that propagation effects due to terrain and atmospheric conditions may be amplifying the actual sound levels by about 6 dB. Parametric analysis using the code has shown that the predominant contributions to MOD-1 rotor noise are: (1) the velocity deficit in the wake of the support tower; (2) the high rotor speed; and (3) off column operation

On Predicting the Phenomenon of Surface Flow Convergence in Wind Farms

A systematic analysis of a single-rotor horizontal axis wind turbine aerodynamics is performed to obtain a realistic potential maximum efficiency. It is noted that by including the effects of swirl, viscosity and finite number of blades, the maximum aerodynamic efficiency of a HAWT is within a few percentage points of the efficiency of commercially-available turbines. The need for investigating windfarm (as a unit) aerodynamics is thus highlighted. An actuator disk model is developed and implemented in the OpenFOAM software suite. The model is validated against 1-D momentum theory, blade element momentum theory, as well as against experimental data. The validated actuator disk model is then used to investigate an interesting microscale meteorological phenomenon called “flow convergence” caused by an array of wind turbines. This phenomenon is believed to be caused by the drop of pressure in wind farms. Wind farm numerical simulations are conducted with various approximations to investigate and explain the flow convergence phenomenon