1,721,095 research outputs found
Improving detection of Mycobacterium avium subsp. paratuberculosis infection in cattle by anamnestic ELISA
No full textSviluppo di strumenti per l'ottimizzazione del progetto aerodinamico di turbomacchine assiali
Full text linkLa tesi propone un modello throughflow inverso da impiegare durante la fase assialsimmetrica del processo di progetto di una turbomacchina. Il modello risolve con tecnica time marching le equazioni meridiane di Eulero, nelle quali un campo di forza volumica normale alle superfici medie delle pale ("blade force") ne riproduce l'azione sul flusso. La geometria delle superfici è ricavata dalla condizione di tangenza, in accordo con la componente tangenziale della "blade force" imposta come dato di progetto. La distribuzione meridiana della blade force sulle regioni palettate del flowpath è definibile attraverso un processo di ottimizzazione inversa. Le equazioni di Eulero contengono anche altri termini destinati a riprodurre gli effetti del bloccaggio delle pale e delle perdite di profilo. La tesi affronta in particolare il problema delle alte deflessioni (pale di turbina), sia sotto l'aspetto fisico, individuando le più opportune condizioni al contorno da associare alle equazioni di Eulero, sia sotto l'aspetto numerico, introducendo uno schema upwind di tipo implicito per contrastare le instabilità che quelle condizioni comportano. Lo schema si rivela molto efficiente e robusto nel generare singole schiere di apertura infinita, non altrettanto se applicato a stadi di turbina completi. Per questa ragione, la tesi indaga anche la variante diretta del modello throughflow, che valuta la "blade force" (e perciò le prestazioni della macchina) a partire da un'assegnata geometria delle superfici medie. Pur con le sue limitazioni, il solutore inverso è ugualmente introdotto in ottimizzatori esistenti, allo scopo di illustrare alcuni esempi di ottimizzazione inversa per configurazioni fortemente defless
Euler-based throughflow method for inverse design and optimization of turbomachinery blades
No full textAn inviscid model for complete axial flow turbomachinery is adopted, which replaces the blades with throughflow surfaces. The main effects of the real blades on the flow are modelled by blade forces. The inverse method predicts the axisymmetric flow field and throughflow surface geometry for a specified distribution of azimuthal inviscid force. This quantity drives the meridional distribution of rotor shaft power. Euler equations are solved by an implicit upwind finite-volume scheme. The time-marching computation includes an evolutionary equation for each throughflow surface, which is solved by implicit finite differences. Standard optimisation algorithms are used to find distributions of azimuthal force that minimise some sample cost functions. The optimal blade shapes are given by the corresponding geometrical solutions of the inverse problem. Since the cost function evaluation is reduced to an inviscid two-dimensional computation, the entire process is significantly less time-consuming than those based on three-dimensional CFD solver
An actuator disk model of incidence and deviation for RANS-based throughflow analysis
No full textReynolds-averaged Navier-Stokes (RANS) equations with blade blockage and blade force source terms are solved in the meridional plane of complete axial flow turbomachinery using a finite-volume scheme. The equations of the compressible actuator disk (AD) are introduced to modify the evaluation of the convective fluxes at the leading and trailing edges (LEs and TEs). An AD behaves as a compact blade force which instantaneously turns the flow with no production of unphysical entropy. This avoids unphysical incidence loss across the LE discontinuity and allows for application of all of the desired deviation at the TE. Unlike previous treatments, the model needs no handmade modification of the throughflow (TF) surface and does not discriminate between inviscid and viscous meridional flows, which allows for coping with strong incidence gradients through the annulus wall boundary layers and with secondary deviation. This paper derives a generalized blade force term that includes the contribution of the LE and TE ADs in the divergence form of the TF equations and leads to generalized definitions of blade load, blade thrust, shaft torque, and shaft power. In analyzing a linear flat plate cascade with an incidence of 32 deg and a deviation of 21 deg, the proposed model provided a 105 reduction of unphysical total pressure loss compared to the numerical solution with no modeling. The computed mass flow rate, blade load, and blade thrust showed excellent agreement with the theoretical values. The complete RANS TF solver was used to analyze a four-stage turbine in design and off-design conditions with a spanwise-averaged incidence of up to 2 deg and 43 deg, respectively. Compared to a traditional streamline curvature solution, the RANS solution with incidence and deviation modeling provided a 0.1 to 0.7% accurate prediction of mass flow rate, shaft power, total pressure ratio, and adiabatic efficiency in both the operating conditions. It also stressed satisfactory agreement concerning the spanwise distributions of flow angle and Mach number at LEs and TEs. In particular, secondary deviation was effectively predicted. The RANS solution with no modeling showed acceptable performance prediction only in design conditions and could introduce no deviation
Euler-based throughflow method for inverse design and optimization of turbomachinery blades
No full textAxisymmetric Design of Axial Turbomachines:an inverse method introducing Profile Losses
No full textThe distributed loss model has been included in a time-marching Euler solver. This predicts the axisymmetric flow field and hub-to-tip stream surface geometry once the loading distribution is prescribed in the blade regions. The loss model replaces shear stresses with a suitable viscous force distribution, which does not work on the relative flow motion, but is only meant to produce entropy along the meridional streamlines. As in a fully inverse computation the flow angles are unknown, empirical loss correlations for single cascades cannot be used. The overall loss level through each blade row will be provided by the one-dimensional stage of the design process, then simplifying assumptions or specific correlations are used to estimate its spanwise distribution. The loss model effects on the flow field and stream surface geometry predicted by the inverse solver have been assessed
Prevalenze anticorpali verso Neospora Caninum nel cane. Indagine sieroepidemiologica in soggetti allevati in ambiente urbano e rurale.
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