Accuracy of the Gamma Re-Theta Transition Model for Simulating the DU-91-W2-250 Airfoil at High Reynolds Numbers

Accurate computation of the performance of a horizontal-axis wind turbine (HAWT) using Blade Element Momentum (BEM) based codes requires good quality aerodynamic characteristics of airfoils. This paper shows a numerical investigation of transitional flow over the DU 91-W2-250 airfoil with chord-based Reynolds number ranging from 3 × 106 to 6 × 106. The primary goal of the present paper is to validate the unsteady Reynolds averaged Navier-Stokes (URANS) approach together with the four-equation transition SST turbulence model with experimental data from a wind tunnel. The main computational fluid dynamics (CFD) code used in this work was ANSYS Fluent. For comparison, two more CFD codes with the Transition SST model were used: FLOWer and STAR-CCM +. The obtained airfoil characteristics were also compared with the results of fully turbulent models published in other works. The XFOIL approach was also used in this work for comparison. The aerodynamic force coefficients obtained with the Transition SST model implemented in different CFD codes do not differ significantly from each other despite the different mesh distributions used. The drag coefficients obtained with fully turbulent models are too high. With the lowest Reynolds numbers analyzed in this work, the error in estimating the location of the transition was significant. This error decreases as the Reynolds number increases. The applicability of the uncalibrated transition SST approach for a two-dimensional thick airfoil is up to the critical angle of attack.

Design And Numerical Analysis of Morphing Airfoil With Corrugated Geometry In The Application MAV’s

The main objective of the work is to enhance the aerodynamic performance during takeoff and cruise by using newly corrugated airfoil of MAV’s by Morphing it at the trailing edge. In this study, the transient nature of corrugated airfoils at low Reynolds number were assumed to be the flow is laminar, incompressible and two dimensional. The newly corrugated geometry which is parameterized from the camber line using a Radial basis function (RBF) based on interpolation method positioned at the lower surface of the airfoil i.e., NACA0015. Five morphed geometries are designed using ANSYS Space claimer. The computational domain is meshed using cartesian grid, the surface meshes with quadrilateral. Numerical simulations are performed with turbulent models i.e., k-omega, k-epsilon and Spalart allmaras. In the analysis, there is an increment of coefficient of lift and decrease in coefficient of drag by varying Reynolds number. Compared to NACA0015, corrugated NACA0015 shows good results.

Impact of Turbulence Models of Wind Pressure on two Buildings with Atypical Cross-Sections

The article deals with the numerical analysis of the wind pressure distribution on a group of two high-rise buildings of different shape for different wind directions. The first building has the shape of a circular cylinder and the second was created by a combination of semicircles and a longitudinal member. The floor plan of the second building was similar to the letter S. The simulations were realized as 3D steady RANS. CFD results were compared with experimental measurements in the wind tunnel of the Slovak University of Technology in Bratislava. The results were processed using statistical methods such as correlation coefficient, fractional bias and fraction of data within a factor of 1.3, which determined the most suitable CFD model. The purpose of the present article was to verify the distribution of the external pressure coefficient on scale models at a scale of 1:350, which are located in the Atmospheric Surface Layer (ASL). In numerical modeling, the most important thing was to ensure similarity with the flow in the experimental Atmospheric Boundary Layer (ABL) and with the flow around the models. SST k–ω was evaluated as the most suitable turbulent model for the given type of problem. Turbulent models had a decisive influence on the overall distribution of external wind pressures on objects. The results showed that the most suitable orientation of the objects in terms of the external wind pressure coefficient is 0°, when the cylinder produced a shielding effect, with min mean cpe = −0.786. The most unfavorable wind effects were shown by the wind direction of 90° and 135° with the value min mean cpe = −1.361.

Turbulent Heat Transfer Characteristics of Supercritical Carbon Dioxide for a Vertically Upward Flow in a Pipe Using Computational Fluid Dynamics and Artificial Neural Network

Modelling of turbulence heat transfer for supercritical fluids using Computational Fluid Dynamics (CFD) software is always challenging due to the drastic property variations near critical point. Use of Artificial Neural Networks (ANN) along with numerical methods have shown promising results in predicting heat transfer coefficients of heat exchangers. In this study, accuracy of four different turbulent models available in the commercial CFD software - Ansys Fluent is investigated against the available experimental results. The k-e Re Normalization Group (RNG) model with enhanced wall treatment is found to be the best-suited turbulence model. Further, K-e RNG Turbulence Model is used in CFD for parametric analysis to generate the data for ANN studies. A total of 1,34,698 data samples were generated and fed into the ANN program to develop an equation that can predict the heat transfer coefficient. It was found that, for the considered range of values the absolute average relative deviation is 3.49%.

Numerical and Physical Modelling of Wave Overtopping on a Smooth Impermeable Dike with Promenade under Strong Incident Waves

This paper presents a study of run-up/overtopping over a smooth impermeable dike with promenade using 2D and 3D mesh-based and mesh-free numerical models and results from 2D physical modelling for strong energetic incident waves. These waves induce plunging wave breaking and a complex water/air mixture turbulent flow before overtopped the dike, a challenging configuration for numerical models. The analysis is structured in two phases: (i) evaluates the results of 2D numerical and physical models for run-up and overtopping; (ii) compares qualitatively the results of 3D numerical models for overtopping over a dike with promenade between groins located in front of a slope beach. The results indicate that the main differences obtained in run-up and overtopping are due to differences in wave generation and active absorption systems used in physical and numerical models and in turbulent models used by the numerical models. These differences lead to changes on incident wave height and on wave breaking and, consequently, on reflection, run-up and overtopping over the structure. For 3D simulation, even if larger discrepancies were found on overtopping along the dike, mean wave overtopping discharge and water flow height at the crest of the groin head show a similar order of magnitude.

Turbulent model validations with CFD/wind tunnel test and application to SEA for wind noise prediction

Wind noise is becoming to have a higher priority in automotive industry. Several past studies investigated whether SEA can be utilized to predict wind noise by applying a turbulent spectrum model as the input. However, there are many kinds of turbulent models developed and the appropriate model for input to SEA is still unclear. Due to this, this paper focuses on clarifying an appropriate turbulent model for SEA simulation. First, the input turbulent pressure spectrum from five models are validated with wind tunnel tests and CFD. Next, a conventional numerical approach is used to validate models from the aspect of response accuracy. Finally, turbulent models are applied to an SEA model developed for a wind tunnel, and the SEA response is validated with test data. From those input/response validations, an appropriate turbulent model is investigated.

Simplified Transition and Turbulence Modeling for Oscillatory Pipe Flows

One-dimensional unsteady Reynolds-averaged Navier–Stokes computations were performed for oscillatory transitional and turbulent pipe flows and the results were validated against existing experimental data for a wide variety of oscillatory Reynolds and Womersley numbers. An unsteady version of the Johnson–King model was implemented with optional near-wall modification to account for temporal pressure gradient variations, and the predictions were compared with those of the Spalart–Allmaras and k–ε turbulence models. Transition and relaminarization were based on empirical Womersley number correlations and assumed to occur instantaneously: in the former case, this assumption was valid, but in the latter case, deviations between data and predictions were observed. In flows where the oscillatory Reynolds numbers are substantially higher than the commonly accepted steady critical value (~2000), fully or continuously turbulent models produced the best correspondence with experimental data. Critically and conditionally turbulent models produced slightly inferior correspondence, and no significant benefit was observed when near-wall pressure gradient effects were implemented or when common one- and two-equation turbulence models were employed. The turbulent velocity profiles were mainly unaffected by the oscillations and this was explained by noting that the turbulent viscosity is significantly higher than its laminar counterpart. Thus, a turbulent Womersley number was proposed for the analysis and categorization of oscillatory pipe flows.