• Energy Research

This study provides a detailed analysis of the aerodynamic performance of various airfoil configurations, focusing on lift coefficient, stall characteristics, and maximum lift-to-drag ratio. The investigation includes the NACA23012C profile and configurations with different step geometries, ranging from one-step to five-step designs. Experimental measurements were conducted using a well-equipped aerodynamic laboratory, Institute of Aviation Engineering and Technology (IAET), Giza, Egypt. The lab features a wind tunnel, propeller test rig, and data acquisition system. The experiments were conducted meticulously to ensure accuracy and reproducibility, with a standardized method employed for uncertainty analysis. The results reveal distinct aerodynamic behaviors among the different configurations, highlighting the significant impact of design variations on aerodynamic performance. Notably, the three-step configuration consistently exhibited high performance, with a competitive or superior lift coefficient across a range of Reynolds numbers, showing an improvement of up to 35.1 %. Similarly, the four-step configuration demonstrated substantial increases in lift-to-drag ratios, reaching up to 53.2 %, while the five-step configuration exhibited varying trends with a minimum drag coefficient. The study also investigated stall characteristics and sensitivity to Reynolds numbers, revealing the complex trade-offs inherent in airfoil design. The findings provide valuable insights into optimizing airfoil performance under different operational conditions. Additionally, the adoption of two and three stepped airfoils resulted in significant reductions in blade material and associated costs for turbine blades.

{"references": ["Blocken, B., Carmeliet, J., Pedestrian Wind Environment around\nBuildings: Literature Review and Practical Examples, Journal of\nThermal Envelope and Building Science, Oct 2004, 28: 107-159;", "Jensen, A. G., Franke, J., Hirsch, C., Schatzmann, M., Stathopoulos, T.,\nWisse, J., Wright, N. G., Impact of Wind and Storm on City Life and\nBuilt Environment - Working Group 2 - CFD Techniques -\nComputational Wind Engineering, Proceedings of the International\nConference on Urban Wind Engineering and Building Aerodynamics,\nCOST Action C14, Von Karman Institute, Rhode-Saint-Gen\u00e8se,\nBelgium, May 5-7, 2004;", "Yoshie, R., Mochida, A., Tominaga, Y., Kataoka, H., Harimoto, K.,\nNozu, T., Shirasawa, T., Cooperative Project for CFD Prediction of\nPedestrian Wind Environment in the Architectural Institute of Japan,\nJournal of Wind Engineering and Industrial Aerodynamics, 95 (2007)\n1551-1578;", "Franke, J., Hirsch, C., Jensen, A. G., Krus, H. W., Schatzmann, M.,\nWestbury, P. S., Miles, S. D., Wisse, J. A., Wright, N. G.,\nRecommendations on the Use of CFD in Wind Engineering, Proceedings\nof the International Conference on Urban Wind Engineering and\nBuilding Aerodynamics, COST Action C14, Von Karman Institute,\nRhode-Saint-Gen\u00e8se, Belgium, May 5-7, 2004;", "Stathopoulos, T., Wind Effects on People, Proceedings of the\nInternational Conference on Urban Wind Engineering and Building\nAerodynamics, COST Action C14, Von Karman Institute, Rhode-Saint-\nGen\u00e8se, Belgium, May 5-7, 2004;", "Ozmen, Y., Van Beeck, J. P. A. J., Baydar, E., The Turbulent Flow over\nThree Dimensional Roof Modles Immersed in an Atmospheric Boundary\nLayer, Proceedings of the International Conference on Urban Wind\nEngineering and Building Aerodynamics, COST Action C14, Von\nKarman Institute, Rhode-Saint-Gen\u00e8se, Belgium, May 5-7, 2004;", "Dalgliesh, W. A., Wind Loads on Low Buildings, Division of Building\nResearch, National Research Council of Canada, Ottawa, January 1981;", "http://www.vki.ac.be/;", "Parmentier, B., Hoxey, R., Buchlin, J. M., Corieri, P., The Assessment of\nFull Scale Experimental Methods for Measuring Wind Effects on Low\nRise Buildings, COST Action C14, Impact of Wind and Storm on City\nLife and Built Environment, June 3-4, 2002, Nantes, France;\n[10] Counihan, J., An Improved Method of Simulating an Atmospheric\nBoundary Layer in a Wind Tunnel, Atmos. Environ., Vol. 3 (1969), pp.\n197-214;\n[11] http://www.vki.ac.be/index.php?option=com_content&view=article&id\n=60:low-speed-wind-tunnel-l-2b&catid=48:low-speed-windtunnels&\nItemid=151."]} The construction of a civil structure inside a urban area inevitably modifies the outdoor microclimate at the building site. Wind speed, wind direction, air pollution, driving rain, radiation and daylight are some of the main physical aspects that are subjected to the major changes. The quantitative amount of these modifications depends on the shape, size and orientation of the building and on its interaction with the surrounding environment.The flow field over a flat roof model building has been numerically investigated in order to determine two-dimensional CFD guidelines for the calculation of the turbulent flow over a structure immersed in an atmospheric boundary layer. To this purpose, a complete validation campaign has been performed through a systematic comparison of numerical simulations with wind tunnel experimental data.Several turbulence models and spatial node distributions have been tested for five different vertical positions, respectively from the upstream leading edge to the downstream bottom edge of the analyzed model. Flow field characteristics in the neighborhood of the building model have been numerically investigated, allowing a quantification of the capabilities of the CFD code to predict the flow separation and the extension of the recirculation regions.The proposed calculations have allowed the development of a preliminary procedure to be used as a guidance in selecting the appropriate grid configuration and corresponding turbulence model for the prediction of the flow field over a twodimensional roof architecture dominated by flow separation.

The unsteady flow field in a reversible pump-turbine is investigated during the continuous load rejection using a 3D computational fluid dynamic analysis. Numerical calculations are carried out using the detached eddy simulation (DES) turbulence model and a new approach involving automatic mesh motion. In this way, the instability of the flow field is analyzed by continuously changing the guide vane openings from the best efficiency point (BEP). Unsteady flow characteristics are described by post-processing signals for several monitoring points including mass flow, torque, head and pressure in the frequency and time-frequency domains. The formation of vortices of different scales is observed from the origin to further enlargement and stabilization; the effect of the rotating structures on the flow passage is analyzed, and the influence of unsteady flow development on the performance of the turbine is investigated. Finally, the evolution during the period of load rejection is characterized in order to determine the hydrodynamic conditions causing the vibrations in the machine.

The work describes a systematic optimization strategy for designing hypersonic inlet intakes. A Reynolds-averaged Navier-Stokes database is mined using genetic algorithms to develop ideal designs for a priori defined targets. An intake geometry from the literature is adopted as a baseline. Thus, a steady-state numerical assessment is validated and the computational grid is tuned under nominal operating conditions. Following validation tasks, the model is used for multi-objective optimization. The latter aims at minimizing the drag coefficient while boosting the static and total pressure ratios, respectively. The Pareto optimal solutions are analyzed, emphasizing the flow patterns that result in the improvements. Although the approach is applied to a specific setup, the method is entirely general, offering a valuable flowchart for designing super/hypersonic inlets. Notably, because high-quality computational fluid dynamics strategies drive the innovation process, the latter accounts for the complex dynamics of such devices from the early design stages, including shock-wave/boundary-layer interactions and recirculating flow portions in the geometrical shaping.

Abstract In this article the performance of a system that integrates a photovoltaic (PV) layer and a phase change material (PCM) layer in a double skin facade (DSF) is investigated. A physical–mathematical model is developed to simulate the dynamic thermal behaviour of the system, and numerical simulations are carried out for different climates (Venice, Helsinki and Abu Dhabi) in order to evaluate the performance of the proposed solution. The numerical model combines different validated codes for the simulation of optical, thermal, and electrical behaviour of PCM, PV and DSF. The model is then coupled with the indoor air heat balance equation to evaluate the impact of the proposed facade system on the heating and cooling energy demand. The adoption of a PCM layer in the DSF cavity, in combination with a semi-transparent PV layer, leads to a reduction in the monthly cooling energy demand in the 20–30% range. This result is particularly relevant for hot climates – where cooling loads are seen throughout the year. The improvement in terms of heating load in more cold-dominated locations is limited. The smoothing of the PV module temperature leads to an increase in the electrical energy converted by the PV, with peak values of improvement in the range of 5–8% when the DSF is equipped with the PCM–PV configuration. Ventilation strategies of the facade cavity, coupled with the correct selection of PCM (and of its transition-phase temperature range), are the key aspects to ensure effective management of the proposed technology.

An off-design steady state model of a generic turboshaft engine has been implemented to assess the influence of variable free power turbine (FPT) rotational speed on overall engine performance, with particular emphasis on helicopter applications. To this purpose, three off-design flight conditions were simulated and engine performance obtained with different FTP rotational speeds were compared. In this way, the impact on engine performance of a particular speed requested from the main helicopter rotor could be evaluated. Furthermore, an optimization routine was developed to find the optimal FPT speed which minimizes the engine specific fuel consumption (SFC) for each off-design steady state condition. The usual running line obtained with constant design FPT speed is compared with the optimized one. The results of the simulations are presented and discussed in detail. As a final simulation, the main rotor speed Ω required to minimize the engine fuel mass flow was estimated taking into account the different requirements of the main rotor and the turboshaft engine.

{"references": ["T. Burton and D. Sharpe, N. Jenkins and E. Bossanyi, E., Wind Energy\nHandbook, John Wiley & Sons, Ltd, Baffins Lane, Chichester - West\nSussex, PO19 1UD, England, 2001, p. 61.", "H. Glauert, Airplane Propellers, Aerodynamic Theory, Dover\nPublication Inc, New York, 1963, Vol. 4, Division L, 169-360.", "R. J. Templin, Aerodynamic Theory for the NRC Vertical-Axis Wind\nTurbine, NRC of Canada TR LTR-LA-160, 1974.", "P. C. Klimas, \"Darrieus Rotor Aerodynamics\", Sandia National\nLaboratories, Advanced Energy Projects Division 4715, Albuquerque,\nNM 87185.", "M. C. Claessens, The Design and Testing of Airfoils for Application in\nSmall Vertical Axis Wind Turbines, Master of Science Thesis, Faculty\nof Aerospace Engineering, Delft University of Technology, November\n9, 2006.", "J. H. Strickland, \"The Darrieus Turbine: A Performance Prediction\nModel Using Multiple Streamtube\", Sandia Report, SAND75-0431.", "S. Read and D. J. Sharpe, \"An Extended Multiple Streamtube Theory\nfor Vertical Axis Wind Turbines\", Department of M.A.P. Engineering\nReport, Kingston Polytechnic, Kingston upon Times, United Kingdom,\n1980.", "I. Paraschivoiu, \"Double-Multiple Streamtube Model for Darrieus Wind\nTurbines\", NASA Conference Publication 2185, May 1981.", "I. Paraschivoiu and F. Delclaux, \"Double Multiple Streamtube Model\nwith Recent Improvements\", Journal of Energy, 7(3), 1983, pp. 250-\n255.\n[10] H. Mc Coy and J. L. Loth, \"Up- and Downwind Rotor Half Interference\nModel for VAWT\", AIAA 2nd Terrestrial Energy Systems Conference,\nColorado Springs, CO, December 1-3, 1981.\n[11] H. Mc Coy and J. L. Loth, \"Optimization of Darrieus Turbines with an\nUpwind and Downwind Momentum Model\", Journal of Energy, 7(4),\n1983, pp. 313-318.\n[12] R. E. Sheldal and C. Klimas, \"Aerodynamic Characteristics of Seven\nSymmetrical Airfoil Sections Through 180-Degree Angle of Attack for\nUse in Aerodynamic Analysis of Vertical Axis Wind Turbines\", Sandia\nNational Laboratories, Energy Report, SAND80-2114, March 1981.\n[13] M. H. Worstell, \"Aerodynamic Performance of the 17 Meter Diameter\nDarrieus Wind Turbine\", Sandia Report, SAND78-1737.\n[14] M. H. Worstell, \"Aerodynamic Performance of the 17-M-Diameter\nDarrieus Wind Turbine in the Three-Bladed Configuration: An\nAddendum\", Sandia Report, SAND79-1753.\n[15] M. O. L. Hansen, Aerodynamics of Wind Turbines, Earthscan, UK and\nUSA, Second Edition, 2008, p. 30.\n[16] H. Glauert, \"A General Theory of the Autogyro\", ARCR R&M, No.\n1111, 1926.\n[17] K. G. Pierce, Wind Turbine Load Prediction using the Beddoes-\nLeishman Model for Unsteady Aerodynamics and Dynamic Stall,\nMaster of Science Thesis, Department of Mechanical Engineering, The\nUniversity of Utah, August 1996.\n[18] C. Masson, C. Leclerc, and I. Paraschivoiu, \"Appropriate Dynamic-Stall\nModels for Performance Predictions of VAWTs with NLF Blades\",\nInternational Journal of Rotating Machinery, 1998, Vol. 4, No. 2, pp.\n129-139.\n[19] R. E. Gormont, \"An Analytical Model of Unsteady Aerodynamics and\nRadial Flow for Application to Helicopter Rotors\", U.S. Army Air\nMobility Research and Development Laboratory Technical Report, pp.\n72-67, 1973.\n[20] J. H. Strickland, B. T. Webster and T. Nguyen, \"A Vortex Model of the\nDarrieus Turbine: an Analytical and Experimental Study\", Sandia\nreport, SAND79-7058.\n[21] B. Mass\u00e9, \"Description de deux programmes d-ordinateur pour le calcul\ndes performance et des charges a\u00e9rodynamiques pour les \u00e9oliennes \u251c\u00e1 axe\nvertical\", IREQ-2379, 1981.\n[22] D. E. Berg, \"An Improved Double-Multiple Streamtube Model for the\nDarrieus-Type Vertical Axis Wind Turbine\", Sixth Biennal Wind\nEnergy Conference and Workshop, pp. 231-233.\n[23] L. Battisti, A. Brighenti and L. Zanne, \"Analisi dell-effetto della scelta\ndell-architettura palare sulle prestazioni di turbine eoliche ad asse\nverticale\" (in Italian), 64\u252c\u2591 Convegno ATI, L-Aquila, Italia, 2009.\n[24] S. Read and D. J. Sharpe, \"An Extended Multiple Streamtube Theory\nfor Vertical Axis Wind Turbines\", 2nd BWEA Workshop, April 1980.\n[25] I. H. Abbot and A. E. Von Doenhoff, Theory of Wing Sections, Dover\nEdition, 1959.\n[26] L. A. Viterna and R. D. Corrigan, \"Fixed Pitch Rotor Performance of\nLarge Horizontal Axis Wind Turbines\", DOE/NASA Workshop on\nLarge Horizontal Axis Wind Turbines, 28-30 July 1981, Cleveland,\nOH."]} A multiple-option analytical model for the evaluation of the energy performance and distribution of aerodynamic forces acting on a vertical-axis Darrieus wind turbine depending on both rotor architecture and operating conditions is presented. For this purpose, a numerical algorithm, capable of generating the desired rotor conformation depending on design geometric parameters, is coupled to a Single/Double-Disk Multiple-Streamtube Blade Element – Momentum code. Both single and double-disk configurations are analyzed and model predictions are compared to literature experimental data in order to test the capability of the code for predicting rotor performance. Effective airfoil characteristics based on local blade Reynolds number are obtained through interpolation of literature low-Reynolds airfoil databases. Some corrections are introduced inside the original model with the aim of simulating also the effects of blade dynamic stall, rotor streamtube expansion and blade finite aspect ratio, for which a new empirical relationship to better fit the experimental data is proposed. In order to predict also open field rotor operation, a freestream wind shear profile is implemented, reproducing the effect of atmospheric boundary layer.

A combined performance/stress numerical analysis is proposed for a three-bladed vertical-axis wind turbine (VAWT) adopting a Blade Element-Momentum (BE-M) algorithm as a simulation tool. After determining the operational curves of the turbine, the aerodynamic forces acting on rotor blades, as well as the global thrust acting on the whole machine, are evaluated as a function of the aerodynamic control strategy of the rotor, obtaining a first estimation to be used for the structural sizing of both rotor blades and shaft.