Edson Luiz Zaparoli

Evaluation of two microscale flow models through two wind climate generalization procedures using observations from seven masts at a complex site in Brazil

Two microscale flow models, a linear and a computational fluid dynamics model solving the Reynolds-averaged Navier–Stokes equations, are evaluated using observations from seven masts at Araripe wind farms, located on a complex terrain area in the northeast region of Brazil. The evaluation is performed by generalizing the wind climate from the masts. By doing so, the effects induced by the local topography on the surface wind are removed, resulting in the background wind field, which is the ideal undisturbed flow over flat terrain with uniform roughness. Here this is performed in two ways: using the time series of 10-min mean winds and using wind speed distributions. Non-negligible differences are found on the generalized winds when comparing the results from the two methods. For both generalization methods, the results obtained using the more complex flow model show significant improvements when compared to those obtained from the linear model at few locations and for particular inflow directions only.

Least Squares Fitting of Computational Fluid Dynamics Results to Measured Vertical Wind Profiles

Microscale numerical modeling is currently the main tool used in wind industry to assess local wind resources. This paper presents a systematic procedure to adjust computational fluid dynamics (CFD) predicted wind profiles to experimental measurements in order to minimize their differences. It can be applied when wind measurements are available. Data from ten masts with several measurement heights from the well-known Bolund hill experiment provided the observed wind profiles. Simulated profiles were calculated with WINDSIM CFD model for the aforementioned site. Speed-up correction factors were defined through the least squares method to cross-correlate each mast as reference to all the others inside the Bolund hill domain. After, the observed and the adjusted wind profiles at the same position were compared. Moreover, root mean square errors (RMSEs) were used as a metric to evaluate the estimations and the ability of each position to be predicted and predictor. Results have shown that the quality of the adjustment process depends on the flow characteristics at each position related to the incoming wind direction. Most affected positions, i.e., when the airflow overcomes the Bolund hill escarpment, present the less accurate wind profile estimations. The reference mast should be installed upstream of the potential wind turbines’ locations and after the main local characteristics of topographical changes. [DOI: 10.1115/1.4036413]

Uma Análise da Aplicação de Três Métodos Estatísticos para o Cálculo do Desvio Padrão da Direção do Vento na Região Tropical

In this paper, a review about three classical methods for calculating the standard deviation of the horizontal wind direction (σθ) is presented. These methods described by Verral and Williams, 1982 (VW), Ackermann, 1983 (ACK), and Yamartino, 1984 (YM) are evaluated by intercomparison between them using wind data obtained from radiosonde measurements. These measurements were taken every six hours over a period of 11 days of September 2008 (dry season of the north of NE region of Brazil, with strong trade winds). Calculations indicated that YM method showed to be the most reliable, whereas the results of VW were very close to YM. Comparing the methods two by two, the maximum differences were 29 degrees between ACK and YM and 26.3 degrees between ACK and VW, while between YM and VW the maximum difference was only 2.6 degrees. According to the reviewed literature, YM is the most stable method over the range of σθ, with maximum error of 2%.

Modeling of aircraft fire suppression system by the lumped parameter approach

Purpose This paper aims to determine the halon concentration time-evolution inside an aircraft cargo compartment to design fire extinguishing systems. Design/methodology/approach A fire suppression system is numerically simulated using the lumped parameter approach. Findings The halon volumetric concentration, halon and air mass fluxes and the cargo compartment pressure are numerically calculated. It also determines the time to halon concentration to achieve the fire suppressant value (high pressure bottle) as well as its inerting volumetric concentration (low pressure bottle). Research limitations/implications In the lumped parameter approach, the dependent variables of interest are a function of time alone, and its spatial distribution is neglected. Practical implications This study predicts the fire extinguishing agent behavior aiming to satisfy cargo compartment certification requirements. Originality/value This paper uses a simplified methodology, but it represents a very useful tool during the preliminary stages of the aircraft fire suppression systems design.

A CFD STUDY OF THE SWIRL NUMBER INDUCED BY A DIESEL ENGINE INTAKE VALVE PORTS

This work focuses on a numerical study of a diesel engine valve ports steady-state compressible flow to calculate the mixing effects due to the presence of the filling and spiral intake ducts. These valve ports have an important role in engine charge exchange (exhaust and intake mechanisms), air-fuel mixture and combustion processes. Diesel engine industry developed a stationary bench flow tests which has been very useful to improve the preliminary design of valve ports. In this bench methodology, a stationary airflow is induced through valve ports by a exhaust fan where pressure drops and swirl flow patterns are measured maintaining a fixed valve aperture. At this context, the present CFD (Computational Fluid Dynamic) work intends to show fluid flow patterns and to calculate the Swirl number induced by the secondary flow. A 3D turbulent steady compressible flow is solved employing a finite volume technique with a density based approach.

Comparison between one-dimensional uncoupled and convection-conduction conjugated approaches in finned surface heat transfer

This work studies the forced convection problem in internal flow between concentric annular ducts, with radial fins at the internal tube surface. The finned surface heat transfer is analyzed by two different approaches. In the first one, it is assumed one-dimensional heat conduction along the internal tube wall and fins, with the convection heat transfer coefficient being a known parameter, determined by an uncoupled solution. In the other way, named conjugated approach, the mathematical model (continuity, momentum, energy and K-e equations) applied to tube annuli problem was numerically solved using finite element technique in a coupled formulation. At first time, a comparison was made between results obtained for the conjugated problem and experimental data, showing good agreement. Then, the temperature profiles under these two approaches were compared to each other to analyze the validity of the one-dimensional classical formulation that has been utilized in the heat exchanger design.