1,720,998 research outputs found
A hierarchical optimisation approach for automatic turbomachinery blade design
No full textThe problem of turbine cascade design is considered using automatic optimisation strategies. Genetic algorithms (GA) have proved, in previous applications, to be able to deal with optimisation problems with many independent variables and to be extremely easy to use into a general computational system. On the other hand GA require a high number of fitness evaluation in order to get the best individual and this aspect is particularly negative when the fitness is obtained from Navier-Stokes computations. In the paper an optimisation strategy to reduce the overall computational time is proposed. It consists of an alternate use of fine and coarse grids for the evaluation of the profile loss with a Navier-Stokes solver developed by the authors. © 2001 by the American Institute of Aeronautics and Astronautics, Inc
A CFD model for real gas flows
No full textNumerical solutions of Navier-Stokes equations are nowadays widely used for several industrial applications in different fields (aerodynamic, propulsion, naval, combustion, etc..), but the solution methods still require significant improvements especially in two aspects: turbulence modeling and fluid modeling. The paper describes in some detail a real fluid model based on Redlich-Kwong-Aungier equation of state and its implementation into a Navier-Stokes solver developed by the authors for turbomachinery flows analysis
A navier-stokes based strategy for the aerodynamic optimisation of a turbine cascade using a genetic algorithm
No full textThe problem of turbine cascade design is considered using automatic optimisation strategies. After the profile parameterisation, two different models are considered to simulate the cascade performances: experimental correlations and a Navier-Stokes code. Interesting considerations on the optimisation algorithm can be drawn using correlations because the evaluation of the fitness is almost instantaneous. By fixing certain of the design constraints two optimised configurations are obtained using simplified correlating function or the viscous flow solver. The optimised configurations are then investigated with an accurate viscous flow computation in order to have a deeper insight into the flowfield. Copyright © 2001 by ASME
Performance Investigation of Airfoils for Axial Flow Fans in Low Solidity Cascades Operating at High Inlet Flow Angles
No full textAxial flow fans are usually characterized by blade sections with low solidity and high inlet flow angles. Two main approaches are followed in the preliminary design phase, to take into account blade interaction effects: the use of available airfoil cascades data (or related correlations) and that of isolated airfoil data together with interference coefficients. The working conditions of low solidity airfoil cascades with highly tangential inflow are not widely studied in the literature, leaving the designer the possibility to rely on limited cascade data or often on the use of isolated airfoil data, with the assumption of negligible interference effects. A systematic investigation of the above working conditions for airfoil cascades is performed with Reynolds-averaged Navier-Stokes simulations. Three different airfoils are used to evaluate the influence of the design lift coefficient and maximum blade thickness. The results provide a better insight into the aerodynamic behavior of airfoil sections in such operating conditions, showing that interactions cannot be neglected. The use of metamodeling coupled with computational fluid dynamics (CFD) simulations is presented as a suitable tool for treating interference effects within the fan design process. The main findings of the present work can be used as a support for design choices as well as for developing design strategies both for the fan blades and for the airfoil sections
Simulation of COVID-19 indoor emissions from coughing and breathing with air conditioning and mask protection effects
No full textThe COVID-19 infection has emerged as a disruptive pandemic at worldwide level. The study of the mechanism of contagion is one of the greatest challenges before a mass vaccination campaign that would protect populations. The study can support the development of knowledge and tools to develop possible strategies for containing its spread in future events. The saliva droplet aerosol expelled during breathing or coughing is the main cause for the propagation of the SARS-Cov-2. In this work, a URANS CFD approach was used to simulate the dispersion from the mouth of these particles in closed environments. The air conditioning system was considered. The conditions were varied to determine their impact on the diffusion of the aerosol. Lagrangian and Eulerian numerical approaches were used to model the coughing and the breathing events. These were validated with the puff theory, numerical and experimental results. A realistic case of a meeting room with two persons was simulated. Different characteristics of the expulsed aerosols and different ventilation system configurations were considered to demonstrate how these simulations can support management strategies for indoor occupation. Finally, the effect of the protective mask was introduced to quantify its beneficial effects to support safe indoor occupation
Three-Dimensional Computational Analysis of Mixed Flow Pumps
No full textConventional time-marching techniques are currently used in industry for three-dimensional compressible flow analysis in different fields (turbomachinery, propulsion, etc...). These techniques have shown strong stability and good accuracy characteristics in many applications, but they are not directly applicable to incompressible flows. A preconditioned time-marching method is described in some details in the paper and the work is focused on a code developed by the authors for mixed-flow pump analysis
Modelling of Incompressible Three-Dimensional Flow in Rotating Turbomachinery Passages
No full textA CFD method, previously developed by the authors for compressible flows, has been modified through a preconditioning technique to account for purely incompressible flows. Such a code is used to compute three-dimensional flows in a mixed flow pump impeller at design and off-design conditions. The results of the inviscid flow approach are critically discussed by comparison to available experimental data
Analisi dell’influenza della modalità di esercizio sui consumi energetici di un impianto di stoccaggio del gas naturale
No full textSimulation and Modeling of Ported Shroud Effects on Radial Compressor Stage Stability Limits
No full textThe design features of a centrifugal compressor must guarantee high performance and a wide operating range. The ported shroud was developed specifically to extend the operating limit. It is a passive flow control device based on a cavity for flow recirculation to avoid blade passage blocking in near surge conditions. A CFD simulation campaign using a simplified model identified the differences in the performance of the centrifugal compressor with ported shroud, compared to the baseline case. The use of a stability criterion to determine the limit mass flow rate, developed in a previous study by the authors, highlighted and quantified the extension of the surge margin in the case with ported shroud for different rotational speeds. An increase in the surge margin of 11% was detected at design speed, but with a lower trend at higher speeds. An in-depth flow analysis showed the main physical mechanisms in the compressor that occur for different operating conditions: at near surge conditions the cavity recirculates the low momentum flow located in the inducer region; it re-energizes the mainstream decreasing the circumferential velocity component; an improvement of up to 7% of the pressure ratio was obtained. Instead, at best efficiency conditions the flow recirculation worsens the performance by reducing the flow incidence at the rotor leading edge. Finally, using unsteady simulations with a complete 3D model and with the application of the stability criterion it was possible to confirm that the ported shroud can effectively extend the operating range
Numerical Prediction of Tonal Noise in Centrifugal Blowers
No full textCentrifugal blowers are widely used in automotive, heating, ventilating, air-conditioning and other industrial purposes. In fact, they allow high-pressure increase to a moderately high mass flow rate, despite the reduced overall dimensions of the system. Numerous authors have worked to increase the fluid dynamic efficiency of the impeller and the volute. However, the recent sound emission standards have imposed tighter constraints, making the noise reduction one of the most challenging target for the design. The reduction of the tonal noise is the main concern for these blowers because the noise at the first harmonic is clearly distinguishable in the noise spectrum. Techniques to reduce this peak generally rely on experimental measurements in aeroacoustics laboratory. In this work, a CFD procedure has been developed to accurately predict the tonal noise in radial bowers. The approach has been validated using real geometries and experimental data. Various turbulence models have been tested to find the best results without the use of excessive computational resources. Moreover, unsteady simulations of the 3D blower have been carried out to analyze the influence of the main geometric parameters on the tonal noise reduction. A parametric design code developed by the authors have been used to change the geometry in order to identify the effect of the main geometrical design parameters on both fluid dynamic and aeroacoustics performance
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