29 research outputs found
Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully- Activated Flapping Foil
Flapping foil energy harvesting systems are considered as highly competitive devices for conventional turbines. Several research projects have already been carried out to improve performances of such new devices. This paper is devoted to study effects of non-sinusoidal heaving trajectory, non-sinusoidal pitching trajectory, and the effective angle of attack on the energy extraction performances of a flapping foil operating at low Reynolds number (Re=1100). An elliptic function with an adjustable parameter S (flattening parameter) is used to simulate various sinusoidal and non-sinusoidal flapping trajectories. The flow around the flapping foil is simulated by solving Navier–Stokes equations using the commercial software Star CCM+ based on the finite-volume method. Overset mesh technique is used to model the flapping motion. The study is applied to the NACA0015 foil with the following kinetic parameters: a dimensionless heaving amplitude h0 = 1c, a shift angle between heaving and pitching motions f = 90 , a reduced frequency f = 0:14, and an effective angle of attack amax varying between 15 and 50 , corresponding to a pitching amplitude in the range q0 = 55:51 to 90:51 . The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = Sq = 1), best performances are obtained for the effective angle of attack, amax = 40 . At small effective angle of attack amax 40 ), non-sinusoidal pitching motion has a negative effect. Performance improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching
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Prediction of cavitation and induced erosion inside a high-pressure fuel pump
The operation of a high-pressure, piston-plunger fuel pump, oriented for use in the common rail circuit of modern Diesel engines for providing fuel to the injectors is investigated in the present study from a numerical perspective. Both the suction and pressurization phases of the pump stroke were simulated with the overall flow time be-ing in the order of 12•10-3 s. The topology of the cavitating flow within the pump con-figuration was captured through the use of an Equation of State (EoS) implemented in the framework of a barotropic, homogeneous equilibrium model. Cavitation was found to set in within the pressure chamber as early as 0.2•10-3 s in the operating cycle, while the minimum liquid volume fraction detected was in the order of 60% during the sec-ond period of the valve opening. Increase of the in-cylinder pressure during the final stages of the pumping stroke lead to the collapse of the previously arisen cavitation structures and three layout locations, namely the piston edge, the valve/valve-seat re-gion and the outlet orifice, were identified as vulnerable to cavitation-induced erosion through the use of cavitation-aggressiveness indicators
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Performance of turbulence and cavitation models in prediction of incipient and developed cavitation
The aim of this article is to assess the impact of turbulence and cavitation models on the prediction of diesel injector nozzle flow. Two nozzles are examined, an enlarged one, operating at incipient cavitation, and an industrial injector tip, operating at developed cavitation. The turbulence model employed includes the re-normalization group k–ε, realizable k–ε and k–ω shear stress transport Reynolds-averaged Navier–Stokes models; linear pressure–strain Reynolds stress model and the wall adapting local eddy viscosity large eddy simulation model. The results indicate that all Reynolds-averaged Navier–Stokes and the Reynolds stress turbulence models have failed to predict cavitation inception due to their limitation to resolve adequately the low pressure existing inside vortex cores, which is responsible for cavitation development in this particular flow configuration. Moreover, Reynolds-averaged Navier–Stokes models failed to predict unsteady cavitation phenomena in the industrial injector. However, the wall adapting local eddy viscosity large eddy simulation model was able to predict incipient and developed cavitation, while also capturing the shear layer instability, vortex shedding and cavitating vortex formation. Furthermore, the performance of two cavitation methodologies is discussed within the large eddy simulation framework. In particular, a barotropic model and a mixture model based on the asymptotic Rayleigh–Plesset equation of bubble dynamics have been tested. The results indicate that although the solved equations and phase change formulation are different in these models, the predicted cavitation and flow field were very similar at incipient cavitation conditions. At developed cavitation conditions, standard cavitation models may predict unrealistically high liquid tension, so modifications may be essential. It is also concluded that accurate turbulence representation is crucial for cavitation in nozzle flows
Design and prediction performance of Venturi injectors in drip irrigation
[EN] The design and prediction performance of four Venturi injector prototypes have been studied using Computational Fluid Dynamics (CFD) techniques. Results were compared with experimental tests carried out in the laboratory of the Universitat Politecnica de Valencia, Valencia, Spain. The analysed and selected geometries for each prototype were used to simulate the operation without nutrient injection (G1) and with nutrient injection (G2). In first case (G1), the results were presented in the form of pressure profile at the injector axe under different velocities and the pressure distribution in the whole geometry. Additionally, this paper analysed the evolution of pressures and head loss versus main water flow in the different prototypes. The relative error was estimated to compare CFD and experimental results. The second case (G2), the graphical representation for the relations between the nutrient aspiration flow and water main flow were obtained for numerical and experiment approaches. In conclusion, CFD techniques appear as a suitable tool for the analysis of the Venturi injector operation, but its validation with experimental data is recommended.[ES] En la Universitat Politècnica de València, Valencia, España, se ha estudiado el diseño y funcionamiento de cuatro
prototipos del inyector Venturi con técnicas de Dinámica de Fluidos Computacional (CFD), comparándo las
con ensayos en laboratorio. Para cada prototipo, las geometrías definidas y analizadas han permitido simular el
funcionamiento sin (G1) y con inyección (G2) para quimigación. En el caso G1, se presentan los gráficos del perfil
de presiones en el eje del inyector para diversas velocidades, así como la distribución del campo de presiones
y de la evolución de las diferencias de presión y pérdidas de carga frente al caudal principal. Para comparar los
resultados obtenidos con CFD frente al resultado experimental, se calculó el error relativo. En el caso G2, se
obtuvo la representación gráfica del el caudal de inyección frente al caudal principal. Las técnicas CFD exigen un
buen ajuste del modelo para dar un resultado aceptable. Son interesantes para comparar geometrías, analizar sus
variantes, realizar prediseños y aproximar ordenes de magnitud, pero es recomendable su ensayo en laboratorio
para validar los resultados.Manzano Juarez, J.; De Azevedo, BM.; Do Bomfim, GV.; Royuela, A.; Palau Estevan, CV.; Viana, TVDA. (2014). Diseño y predicción del funcionamiento de inyectores Venturi en riego localizado. Revista Brasileira de Engenharia Agrícola e Ambiental - Agriambi. 18(12):1209-1217. doi:10.1590/1807-1929/agriambi.v18n12p1209-1217S120912171812Baylar, A., Aydin, M., Unsal, M., & Ozkan, F. (2009). Numerical Modeling of Venturi Flows for Determining Air Injection Rates Using Fluent V6.2. Mathematical and Computational Applications, 14(2), 97-108. doi:10.3390/mca14020097CIPOLLA, E., Silva, F., FILHO, G., & BARROS, R. (2011). Avaliação da Distribuição de Velocidades em Uma Bomba Centrífuga Radial Utilizando Técnicas de CFD. Revista Brasileira de Recursos Hídricos, 16(3), 71-79. doi:10.21168/rbrh.v16n3.p71-79Davis, J. A., & Stewart, M. (2002). Predicting Globe Control Valve Performance—Part I: CFD Modeling. Journal of Fluids Engineering, 124(3), 772-777. doi:10.1115/1.1490108Coutier-Delgosha, O., Fortes-Patella, R., & Reboud, J. L. (2003). Evaluation of the Turbulence Model Influence on the Numerical Simulations of Unsteady Cavitation. Journal of Fluids Engineering, 125(1), 38-45. doi:10.1115/1.1524584Franklin, R. E., & Wallace, J. M. (1970). Absolute measurements of static-hole error using flush transducers. Journal of Fluid Mechanics, 42(1), 33-48. doi:10.1017/s0022112070001052Guo, B., Langrish, T. A. ., & Fletcher, D. F. (2002). CFD simulation of precession in sudden pipe expansion flows with low inlet swirl. Applied Mathematical Modelling, 26(1), 1-15. doi:10.1016/s0307-904x(01)00041-5Hatano, S., Kang, D., Kagawa, S., Nohmi, M., & Yokota, K. (2014). Study of Cavitation Instabilities in Double-Suction Centrifugal Pump. International Journal of Fluid Machinery and Systems, 7(3), 94-100. doi:10.5293/ijfms.2014.7.3.094Lindau, J. W., Kunz, R. F., Boger, D. A., Stinebring, D. R., & Gibeling, H. J. (2002). High Reynolds Number, Unsteady, Multiphase CFD Modeling of Cavitating Flows. Journal of Fluids Engineering, 124(3), 607-616. doi:10.1115/1.1487360Norton, T., Sun, D.-W., Grant, J., Fallon, R., & Dodd, V. (2007). Applications of computational fluid dynamics (CFD) in the modelling and design of ventilation systems in the agricultural industry: A review. Bioresource Technology, 98(12), 2386-2414. doi:10.1016/j.biortech.2006.11.025Palau-Salvador, G., Gonzalez Altozano, P., & Arviza-Valverde, J. (2007). Numerical modeling of cavitating flows for simple geometries using FLUENT V6.1. Spanish Journal of Agricultural Research, 5(4), 460. doi:10.5424/sjar/2007054-269Palau-Salvador, G., González-Altozano, P., & Arviza-Valverde, J. (2007). Three-Dimensional Modeling and Geometrical Influence on the Hydraulic Performance of a Control Valve. Journal of Fluids Engineering, 130(1). doi:10.1115/1.2813131Reader-Harris, M. ., Brunton, W. ., Gibson, J. ., Hodges, D., & Nicholson, I. . (2001). Discharge coefficients of Venturi tubes with standard and non-standard convergent angles. Flow Measurement and Instrumentation, 12(2), 135-145. doi:10.1016/s0955-5986(01)00007-3Singhal, A. K., Athavale, M. M., Li, H., & Jiang, Y. (2002). Mathematical Basis and Validation of the Full Cavitation Model. Journal of Fluids Engineering, 124(3), 617-624. doi:10.1115/1.1486223Sun, Y., & Niu, W. (2012). Simulating the Effects of Structural Parameters on the Hydraulic Performances of Venturi Tube. Modelling and Simulation in Engineering, 2012, 1-7. doi:10.1155/2012/458368Teruel, B. J. (2010). Controle automatizado de casas de vegetação: variáveis climáticas e fertigação. Revista Brasileira de Engenharia Agrícola e Ambiental, 14(3), 237-245. doi:10.1590/s1415-43662010000300001Vortmann, C., Schnerr, G. H., & Seelecke, S. (2003). Thermodynamic modeling and simulation of cavitating nozzle flow. International Journal of Heat and Fluid Flow, 24(5), 774-783. doi:10.1016/s0142-727x(03)00003-1Wei, Q., Shi, Y., Dong, W., Lu, G., & Huang, S. (2006). Study on hydraulic performance of drip emitters by computational fluid dynamics. Agricultural Water Management, 84(1-2), 130-136. doi:10.1016/j.agwat.2006.01.016Xing, T., & Frankel, S. H. (2002). Effect of Cavitation on Vortex Dynamics in a Submerged Laminar Jet. AIAA Journal, 40(11), 2266-2276. doi:10.2514/2.1563Yeoh, G. H., Liu, C., Tu, J., & Timchenko, V. (2012). Computational Fluid Dynamics and Its Applications 2012. Modelling and Simulation in Engineering, 2012, 1-2. doi:10.1155/2012/61061
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Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows
The flow inside a purpose built enlarged single-orifice nozzle replica is quantified using time-averaged X-ray micro-computed tomography (micro-CT) and high-speed shadowgraphy. Results have been obtained at Reynolds and cavitation numbers similar to those of real-size injectors. Good agreement for the cavitation extent inside the orifice is found between the micro-CT and the corresponding temporal mean 2D cavitation image, as captured by the high-speed camera. However, the internal 3D structure of the developing cavitation cloud reveals a hollow vapour cloud ring formed at the hole entrance and extending only at the lower part of the hole due to the asymmetric flow entry. Moreover, the cavitation volume fraction exhibits a significant gradient along the orifice volume. The cavitation number and the needle valve lift seem to be the most influential operating parameters, while the Reynolds number seems to have only small effect for the range of values tested. Overall, the study demonstrates that use of micro-CT can be a reliable tool for cavitation in nozzle orifices operating under nominal steady-state conditions