Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and Computational Fluid Dynamics

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
David Holst ◽  
Francesco Balduzzi ◽  
Alessandro Bianchini ◽  
Benjamin Church ◽  
Felix Wegner ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Technical Literature ◽  
Open Field Behavior ◽  
Static And Dynamic Analysis ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Low Reynolds ◽  
Insight Into

The wind industry needs airfoil data for ranges of angle of attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 deg are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and poststall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140 k and Re = 180 k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behavior. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.

Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD

2018 ◽  
Author(s):  
Francesco Balduzzi ◽  
Alessandro Bianchini ◽  
Giovanni Ferrara ◽  
David Holst ◽  
Benjamin Church ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Pressure Coefficient ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Technical Literature ◽  
Static And Dynamic Analysis ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Low Reynolds ◽  
Insight Into

The wind industry needs airfoil data for ranges of Angle of Attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 degree are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and post stall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140k and Re = 180k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.

Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers: Drag and Moment Coefficients

2019 ◽  
Author(s):  
David Holst ◽  
Francesco Balduzzi ◽  
Alessandro Bianchini ◽  
Christian Navid Nayeri ◽  
Christian Oliver Paschereit ◽  
...  
Keyword(s):  
Experimental Data ◽  
Wind Tunnel ◽  
Wind Turbines ◽  
Reynolds Numbers ◽  
Correction Method ◽  
Hysteresis Cycle ◽  
Low Reynolds Numbers ◽  
Static And Dynamic Analysis ◽  
Wide Range ◽  
Low Reynolds

Abstract Wind industry needs high quality airfoil data for a range of the angle of attack (AoA) much wider than that often provided by the technical literature, which often lacks data i.e. in deep- and post-stall region. Especially in case of vertical axis wind turbines (VAWTs), the blades operate at very large AoAs, which exceed the range of typical aviation application. In a previous study, some of the authors analyzed the trend of the lift coefficient of a NACA 0021 airfoil, using the suggestions provided by detailed CFD analyses to correct experimental data at low Reynolds numbers collected in an open-jet tunnel. In the present study, the correction method is extended in order to analyze even the drag and moment coefficients over a wide range of AoAs for two different Reynolds numbers (Re = 140k and Re = 180k) of particular interest for small wind turbines. The utility of these data is again specifically high in case of VAWTs, in which both the drag and the moment coefficient largely contribute to the torque. The investigation involves tunnel data regarding both static polars and dynamic sinusoidal pitching movements at multiple reduced frequencies. Concerning the numerical simulations, two different computational domains were considered, i.e. the full wind tunnel and the open field. Once experimental data have been purged by the influence of the wind tunnel by means of the proposed correction method, they were compared to existing data for similar Reynolds both for the NACA0021 and for similar airfoils. By doing so, some differences in the static stall angle and the extent of the hysteresis cycle are discussed. Overall, the present paper provides the scientific community with detailed analysis of low-Reynolds NACA 0021 data in multiple variations, which may enable, inter alia, a more effective VAWT design in the near future.

The influence of the flow separation bubble and transition location on the profile drag of three 4-digit NACA aerofoil profiles

2021 ◽  
pp. 0309524X2110550
Author(s):  
Moutaz Elgammi ◽  
Tonio Sant ◽  
Atiyah Abdulmajid Ateeah
Keyword(s):  
Wind Tunnel ◽  
Flow Separation ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Force Balance ◽  
Navier Stokes ◽  
Separation Mechanism ◽  
Numerical Work ◽  
Low Reynolds Numbers ◽  
Low Reynolds

Modeling of the flow over aerofoil profiles at low Reynolds numbers is difficult due to the complex physics associated with the laminar flow separation mechanism. Two major problems arise in the estimation of profile drag: (1) the drag force at low Reynolds numbers is extremely small to be measured in a wind tunnel by force balance techniques, (2) the profile drag is usually calculated by pressure integration, hence the skin friction component of drag is excluded. In the present work, three different 4-digit NACA aerofoils are investigated. Measurements are conducted in an open-ended subsonic wind tunnel, while numerical work is performed by time Reynolds-averaged Navier Stokes (RANS) coupled with the laminar-kinetic-energy ( K-kl-w) turbulence model. The influence of the flow separation bubbles and transition locations on the profile drag is discussed and addressed. This paper gives important insights into importance of measurements at low Reynolds numbers for better aerodynamic loads predictions.

NUMERICAL CHARACTERIZATION OF THE FLOW FIELD IN A FOUR-GENERATION AIRWAY

2008 ◽  
Vol 08 (01) ◽  
pp. 55-74 ◽  
Author(s):  
T. C. LAI ◽  
Y. S. MORSI ◽  
M. SINGH
Keyword(s):  
Reynolds Numbers ◽  
Bronchial Tree ◽  
Secondary Flows ◽  
Fourth Generation ◽  
Numerical Characterization ◽  
Wide Range ◽  
Symmetrical Model ◽  
Computational Fluid Dynamics Cfd ◽  
Insight Into

In this paper, various aspects of respiratory airflow generated from the branching network of tubes that make up the tracheal-bronchial tree are numerically analyzed using the computational fluid dynamics (CFD) package CFX. The model used is a four-generation airway that is geometrically similar to Weibel's symmetrical model. In the present analysis, two different models (in-plane and off-plane) are examined for a wide range of Reynolds numbers that correspond to human breathing conditions. The findings indicate that the secondary flow patterns generated become more significant as the flow passes from the trachea to the fourth-generation airway. Moreover, comparison between in-plane and off-plane models shows that the skewed velocity profiles and secondary flows for the in-plane model are more prominent than those for the off-plane one. In general, the model developed in this study is capable of providing an overall insight into the effect of fluid flow in multiple generations of the human upper respiratory airways.

On transition in a pipe. Part 2. The equilibrium puff

1975 ◽  
Vol 69 (2) ◽  
pp. 283-304 ◽  
Author(s):  
I. Wygnanski ◽  
M. Sokolov ◽  
D. Friedman
Keyword(s):  
Pipe Flow ◽  
Reynolds Numbers ◽  
Turbulent Pipe Flow ◽  
Hot Wire ◽  
Low Reynolds Numbers ◽  
Onset Of Turbulence ◽  
Large Perturbation ◽  
Low Reynolds ◽  
Insight Into ◽  
Type Of Transition

Conditionally sampled hot-wire measurements were taken in a pipe at low Reynolds numbers (2700 > Re > 2000) corresponding to the onset of turbulence as a result of a large perturbation in the flow. This type of transition gives rise to a turbulent puff which maintains itself indefinitely at around Re = 2200. The structure of puffs was investigated in some detail and was found to be very different from the structure of fully developed turbulent pipe flow. Nevertheless, it is independent of the character of the disturbance which created it. The purpose of the study was to gain some insight into the mechanism of transition in a pipe.

Inertial focusing of spherical particles in rectangular microchannels over a wide range of Reynolds numbers

Lab on a Chip ◽  
2015 ◽  
Vol 15 (4) ◽  
pp. 1168-1177 ◽  
Author(s):  
Chao Liu ◽  
Guoqing Hu ◽  
Xingyu Jiang ◽  
Jiashu Sun
Keyword(s):  
Reynolds Numbers ◽  
Spherical Particles ◽  
Rectangular Microchannels ◽  
Inertial Focusing ◽  
Wide Range ◽  
Physical Insight ◽  
Insight Into

This work provides physical insight into the multiplex focusing of particles in rectangular microchannels with different geometries and Reynolds numbers.

scholarly journals Experimental and Numerical Icing Penalties of an S826 Airfoil at Low Reynolds Numbers

Aerospace ◽  
2020 ◽  
Vol 7 (4) ◽  
pp. 46 ◽  
Author(s):  
Richard Hann ◽  
R. Jason Hearst ◽  
Lars Roar Sætran ◽  
Tania Bracchi
Keyword(s):  
Wind Tunnel ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
3D Printed ◽  
Numerical Tools ◽  
Low Reynolds ◽  
Performance Penalty ◽  
High Reynolds ◽  
Ice Shapes

Most icing research focuses on the high Reynolds number regime and manned aviation. Information on icing at low Reynolds numbers, as it is encountered by wind turbines and unmanned aerial vehicles, is less available, and few experimental datasets exist that can be used for validation of numerical tools. This study investigated the aerodynamic performance degradation on an S826 airfoil with 3D-printed ice shapes at Reynolds numbers Re = 2 × 105, 4 × 105, and 6 × 105. Three ice geometries were obtained from icing wind tunnel experiments, and an additional three geometries were generated with LEWICE. Experimental measurements of lift, drag, and pressure on the clean and iced airfoils have been conducted in the low-speed wind tunnel at the Norwegian University of Science and Technology. The results showed that the icing performance penalty correlated to the complexity of the ice geometry. The experimental data were compared to computational fluid dynamics (CFD) simulations with the RANS solver FENSAP. Simulations were performed with two turbulence models (Spalart Allmaras and Menter’s k-ω SST). The simulation data showed good fidelity for the clean and streamlined icing cases but had limitations for complex ice shapes and stall.

Effects of Flow Separation on a Highly Loaded, Low-Pressure Gas Turbine Blade at Low Reynolds Numbers

2015 ◽  
Author(s):  
Tyler M. Pharris ◽  
Olivia E. Hirst ◽  
Kenneth W. Van Treuren
Keyword(s):  
Wind Tunnel ◽  
Gas Turbine ◽  
Flow Separation ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Low Flow ◽  
Turbine Wheel ◽  
Low Pressure Turbine ◽  
Low Reynolds

Current gas turbine engines experience a loss in performance due to the low Reynolds number flow in the low-pressure turbine. This low flow speed can result in separation of the air from the blade surface, reducing the efficiency of the engine. The Baylor University Cascade wind tunnel (BUC) is being used to study this flow separation. A cascade wind tunnel contains a row of turbine vanes that simulates a turbine wheel. The BUC is capable of simulating the environment seen by the low-pressure turbine at high altitudes by producing Reynolds numbers varying from 25,000 to 400,000. The L1A blade profile is currently being tested. Coefficient of pressure (Cp) plots show a less than 1% difference between surface pressure locations when comparing the most inboard and outboard test blades. This agreement demonstrates the flow uniformity in the tunnel. Cp plots also compared favorably to the literature, validating the BUC operation and providing insight into how Reynolds numbers and free stream turbulence intensity (FSTI) affect flow separation. The literature and this study showed the size and reattachment of the separation bubble was highly dependent on the FSTI for lower Reynolds numbers (25,000 to 200,000). This comparison also showed that the size of the separation bubble and the location was not heavily impacted by FSTI for Reynolds numbers above 200,000. Tests in the future will be conducted to determine the actual FSTI of the BUC. Once completely validated, future studies with the BUC may include use of particle image velocimetry (PIV) to visualize the flow, a gold foil steady state technique using liquid crystals to measure heat transfer, and a series of deposition tests using surface roughness (sandpaper or textured sprays) to measure performance loss under these conditions. The ultimate goal of this research is to improve blade design in the low pressure turbine for all commercial and military aircraft.

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