Numerical and experimental analysis of micro HAWTs designed for wind tunnel applications

In this paper the authors describe a design and optimization process of micro HAWTs using a numerical and experimental approach. An in-house 1D BEM model was used to obtain a first geometrical draft. It allowed to quickly optimize blade geometry to maximize energy production as well. As these models are quite sensitive to airfoil coefficients, above all at low Reynolds numbers, an accurate 3D CFD model was developed to support and validate the 1D BEM design, analyzing and fixing the discrepancies between model output. The 3D CFD model was developed and optimized using ANSYS Fluent solver and a RANS transition turbulence model. This allowed to correctly reproduce the transition and stall phenomena that characterize the aerodynamic behavior of micro wind turbines, solving the issues related to low Reynolds flows. The procedure was completed, thus building two micro HAWTs with different scales, testing them in the subsonic wind tunnel of the University of Catania. Wind tunnel features, experimental set-up and testing procedures are presented in the paper. Through the comparison of numerical CFD and experimental test results, a good compatibility was found. This allowed the authors to analyze and compare numerical calculation results and verify blockage effects on the prototypes as well

Evaluation of Oral Mucosal Lesions in 598 Referred Iranian Patients

The mucosal membrane of the oral cavity displays at times classical developmental lesions considered to be variations of normal structures rather than having disease characteristics. Of these lesions leukoedema, Fordyce granules, geographic-, fissured- and hairy tongue, median rhomboid glossitis and lingual varices were studied in 598 patients referred to the School of Dentistry, Tehran, Iran. The prevalence was studied in relation to age, gender, occupation, education, smoking habits, general health, addictions and or drug therapies. Oral developmental lesions were seen in 295 patients (49.3%). Only Fordyce granules (27,9%), fissured tongue (12,9%), leukoedema (12,5%) and hairy tongue (8,9%) had enough cases for statistical analysis. Three of these lesions increased with age but not fissured tongue. All were more common in men. After adjusting for age, the parameters education, occupation and complaints upon referral had little influence on the prevalence of the lesions. Fewer Fordyce granules were seen in oral mucosa of smoking men. Leukoedema and hairy tongue were significantly associated with smoking, leukoedema with diabetes mellitus. We conclude that there was a highly significant association between these oral lesions and age, gender and smoking. Few significant associations were found between oral lesions and general diseases

Boundary layer suction modeling based on the DLR TAU-Code effusion mass flux boundary condition

The aeroelastic assessment of hybrid laminar flow control systems for transport aircraft requires well suited computational models to represent the suction system. This paper presents the application of a non-zero wall-normal velocity boundary condition in the DLR TAU-Code to model an active suction system for laminar flow control. First, the computational laminar velocity profile on a flat plate with homogeneous suction is compared to the analytical solution. Second, the suction boundary condition is tested in combination with a correlation-based transition model and compared to experimental data for a NACA airfoil. In addition, a generic test case is used to demonstrate the effect of a suction system on the steady and unsteady aerodynamics of an airfoil in a transonic, high Reynolds number flow

Assessment and Modification of the γ-Reθ Transition Model Behavior Outside the Boundary Layer

The behavior of the local correlation-based γ−Reθ transition model outside the boundary layer was investigated. It is shown that for perturbed vorticity distributions in the wake the intermittency drops below one. To investigate and quantify this effect, a test case consisting of two NLF(1)-0416 airfoils was simulated imitating a wing tailplane interaction of an aircraft. As a remedy two model modifications are proposed to eliminate the undesired effects. Besides, based on Reynolds-Averaged Navier-Stokes computations a theoretical analyses was performed identifying the stability properties of the original and modified γ equation

Towards CFD-based Aeroelastic Analysis of NLF Wings

The effect of Natural Laminar Flow (NLF) on the aeroelastic behavior of transport aircraft wings is widely unknown. This numerical study investigates the influence of boundary layer transition on the unsteady aerodynamic response of an NLF test case, the DLR-F5 wing. State-of-the-art RANS methods for transition prediction are compared at wind tunnel and free-flight conditions. A more critical flutter behavior is indicated in the case of transitional flow

Transition turbulence model calibration for wind turbine airfoil characterization through the use of a Micro-Genetic Algorithm

Abstract The aerodynamic characterization of airfoils is of crucial importance for the design and optimization of wind turbines. The present paper tries to provide an engineering methodology for the improvement of the accuracy and reliability of 2D airfoil computational fluid dynamics models, by coupling the ANSYS Fluent solver and a Micro-Genetic Algorithm. The modeling strategy provided includes meshing optimization, solver settings, comparison between different turbulence models and, mainly, the calibration of the local correlation parameters of the transition turbulence model by Menter, which was found to be the most accurate model for the simulation of transitional flows. Specifically, the Micro-Genetic Algorithm works by generating populations of the missing local correlation parameters. In doing so, it is possible to search for the minimization of the error in lift calculations. For each specific Reynolds number, the calibration was carried out only at the Angle of Attack where the lift drop occurs and the airfoil completely stalls. This new idea allowed for a relatively rapid and good calibration as demonstrated by the experimental–numerical comparisons presented in this paper. Only the experimental stall angle and the relative lift coefficient were, therefore, necessary for obtaining a good calibration. The calibration was made using the widely known S809 profile data. The correlation parameters, obtained as so, were subsequently used for testing on the NACA 0018 airfoil with satisfactory results. Therefore, the calibration obtained using the S809 airfoil data appeared to be reliable and may be used for the simulation of other airfoils. This can be done without the need for further wind tunnel experimental data or recalibrations. The proposed methodology will, therefore, be of essential help in obtaining accurate aerodynamic coefficients data. This will drastically improve the capabilities of the 1D design codes at low Reynolds numbers thanks to the possibility of generating accurate databases of 2D airfoil aerodynamic coefficients. The advantages of the proposed calibration will be helpful in the generation of more accurate 3D wind turbine models as well. The final objective of the paper was thus to obtain a fine and reliable calibration of the transition turbulence model by Menter. This was specifically made for an accurate prediction of the aerodynamic coefficients of any airfoil at low Reynolds numbers and for the improvements of 3D rotor models