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1
Content available remote Experimental and Numerical Investigation of Small Axial Turbines
EN
The authors conducted a series of experimental studies using a flow tunnel to determine the hydrodynamic characteristics of small axial turbines. The results obtained were confronted with the results obtained from the authors’ own numerical codes based on vortex methods. This article describes the experiment and the numerical method and also discusses the results obtained.
2
Content available remote Towards the Design of Low Noise Level Wind Turbines
EN
According to the authors’ hypothesis generation of high intensity noise is caused by generation of vorticity structures inducing velocities that can be locally higher than the velocity of sound. The localization and magnitude of vorticity concentration can be precisely defined on the basis of a double layer vortex model. Knowing the localization and mechanism of generation of significantly high induced velocities, turbine blades can be shaped in such a way so as to decrease the concentration of vorticity in these zones. According to the hypothesis described in this paper, a modification of turbine blades at the design stage results in their quieter operation for higher loads and wind velocities. The authors base their hypothesis on the experience from design works concerning low noise ship propellers. The following paper focuses on these tasks.
EN
The paper presents problems connected with solving 3D circulation problems. The existence of vortex singularities in the flow behind a body is a characteristic feature of such problems. The vortices influence the velocity and pressure fields in the vicinity of a body. A proposition of rational merging the methods based on the N-S equation together with vortex methods (based on the vorticity equation) is discussed. Such a connection enables accurate and efficient determination of vortex singularities in the flow behind a body.
4
Content available Numerical investigation of the flow around wing tips
EN
The paper dwells with the problems of modelling the flow around a wing tip and tip vortex cavitation. The theoretical bases of the vorticity method and vorticity calculation models for design and estimation of hydrodynamic characteristics of the hydrofoil are presented. Basic assumptions of a double layer lifting surface model are described. A double layer lifting surface model enables proper modelling of the phenomena occurring in the flow around a hydrofoil tip and especially the generation of a free vortices system.
EN
The paper presents an application of non-iterative lifting line theory of Horizontal Axis Wind Turbine (HAWT) to determination of HAWT's performance. The presented model is developed on the basis of modified Witoszyński's propeller theory presented in [4]. In this model an iterative determination of induced velocity field is avoided thanks to solution method similar to as in Witoszyński's propeller theory. The Goldstein kappa factor or Prandtl tip loss factor is introduced to the equations of momentum and angular momentum for ideal HAWT. Ideal axial force (trust) and ideal torque are determined using blade element method (BEM). These values of thrust and torque are compared to those obtained from momentum and torque equation. Thanks to approximation of lift force coefficient vs. angle of attack by sine curve one may obtain a quadratic equation for axial velocity component. The section drag is incorporated to calculations of thrust and power, when induced velocity components are known, and hence angle of attack is determinated. For case of moderately loaded HAWT disc an iterative process for determination of tip loss factor is incorporated. To icorporete sffect of blade element stall-delay due to blade rotation a simple semiempirical model proposed by Tangler and Selig was applied.
PL
W artykule przedstawiono zastosowanie nieiteracyjnej uproszczonej teorii wirowej do wyznaczania charakterystyk silnika wiatrowego o poziomej osi obrotu. Zastosowany model stanowi rowinięcie zmodyfikowanej metody Witoszyńskiego, służącej do wyznaczania charakterystyk śmigła [4]. W modelu tym unika się iteracyjnego wyznaczania prędkości indukowanych dzięki aproksymowaniu profilowej charakterystyki sinusoidą. Porównanie elementarnego oporu wirnika i elementarnego momentu obrotowego obliczonego dla elementu lopaty z ich wartościami uzyskanymi na podstawie zasad zachamowania masy pędu i momentu pędu, pozwala na uzyskanie równania kwadratowego pozwalającego obliczyć lokalną wartość prędkości osiowej. W analizie elementu łopaty wiatraka idealnego dokonuje się korekty wartości cyrkulacji za pomocą współczynnika straty pędu F zaproponowanego przez L. Prandtla. Wyznaczanie kinematyki napływu pozwala na określenie wartości kąta natarcia i oporu profilowego łopaty. Znajomość współczynników siły nośnej i oporu oraz kata napływu umożliwia obliczenie mocy i siły opory wirnika. W celu uwzględnienia wpływu ruchu obrotowego łopat na opóźnienie oberwania warstwy przyściennej zastosowano prosty, półempiryczny model Tanglera-Seliga.
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