Session: 11.1.1 - Advances in Fluids Engineering Education I

Paper Number: 158066

158066 - The complex structure of the flow around a sphere: a numerical & experimental investigation 

Abstract: 

The flow around a sphere occurs very frequently in nature and technology and in different scales. Examples are the flow around small particles but also around sports equipment such as tennis balls or and much larger, around a hot air balloon.

In the present contribution, the flow around a sphere was experimentally investigated in the wind tunnel (Göttinger type) of the Laboratory for Fluid Mechanics and Turbomachinery at Coburg University of Applied Sciences. For this purpose, the flow field was systematically measured using a 5-hole pressure probe (Vectoflow iProbe) and visualized in real time using the Streamwise ProCap system (Streamwise ProCap Professional) via a triangulation method with the tracking camera (OptiTrack V120:Trio). This real time flow visualization also has advantages in the field of engineering education since a comprehensive understanding of the existing flow structures can be visualized in real time in the lab.

In addition to the experimental investigations, a numerical CFD simulation model of the wind tunnel with the sphere was developed with ANSYS FLUENT 2024R2 and the flow around the sphere was simulated analogously to the physical experiment. A detailed grid study based on the Richardson extrapolation has been carried out. The velocity profile in the wind tunnel was measured in advance using a hot wire anemometer and used as boundary conditions in the CFD modeling.

Finally, the drag force of the sphere was measured using a 6-component balance and the drag coefficient cw was computed and plotted as a function of the Reynolds number Re and compared also with the CFD results. In addition, the numerical simulated and experimental measured flow structures are shown and compared in detail. In such a way it was possible to show numerically and experimentally in a fluid mechanics course how the Reynolds number influences the flow pattern and the drag coefficient of the flow around the sphere. The theory, the numerical results as well as the experimental measurements are explained and shown in detail.

Presenting Author: Philipp Epple Coburg University of Applied Sciences

Presenting Author Biography: Philipp Epple has been a full professor for fluid mechanics and turbomachinery at the Faculty of Mechanical Engineering at Coburg University since 2011. He received his doctorate with distinction in mechanical engineering from the Friedrich-Alexander University Erlangen-Nuremberg. He teaches lectures in fluid mechanics, turbomachinery, numerical fluid mechanics (CFD), thermodynamics, heat transfer, wind energy and related areas. He has worked on the design and CFD computation of turbomachinery and has carried out CFD computations for a variety of machines, such as fans with diameters from a few centimeters to over two meters, wind turbines, a high-speed ICE train, large sewage and small blood pumps. He has built various standard turbomachinery test benches and wind tunnels for subsonic and supersonic operation. He has worked on over 50 research and industry projects in the field of turbomachinery and fluid mechanics. He has over 100 peer-reviewed publications. He is an ASME Fellow, has served as a member of the ASME FED Executive Committee, and as Chairman of the ASME FED. He also served as Associate Editor of the ASME Journal of Fluids Engineering for six years (two terms).