The flow field around a two-dimensional slightly modified NACA 643 618 airfoil was investigated for two chord Reynolds numbers, Re = 64, 200 and Re = 137, 000. Surfacepressure distributions and total aerodynamic forces were measured for angles of attack in the range of 12 ◦ to 20 ◦ . Experimental results were compared to numerical results obtained by Direct Numerical Simulations and calculations using the two-dimensional design code XFOIL. Additionally, acoustic measurements and flow-visualizations were performed to study the transition and the separation behavior of the flow for various angles of attack. For certain angles of attack, separation bubbles developed which had a strong influence the airfoil performance. Using the combined approach, experimental and numerical, a deeper insight into the underlying physical mechanisms and into the separation and transition behavior of the boundary layer around the airfoil was obtained. Based on these results, passive and active flow-control strategies were investigated. The flow-control strategies aimed at improving the overall airfoil performance by preventing or at least reducing regions of separated flow.

Experimental Investigation of Separation and Separation Control on a Laminar Airfoil

Assessment of spanwise domain size effect on the transitional flow past an airfoil

Earlier research for the NACA 64 3 -618 airfoil has shown that lift-curve and stall behavior change noticeably when the chord Reynolds number is reduced significantly below its design value. For the same airfoil and a Reynolds number based on chord of Re = 64, 200, separation control by pulsed vortex generator jets and a two-dimensional volume forcing that was motivated by a plasma actuator were investigated. Pulsed vortex generator jets with moderate jet velocities and the two-dimensional volume forcing were found to introduce coherent spanwise structures that are highly effective for separation control. A linear stability analysis of the time-averaged flow showed that spanwise disturbances are amplified by an instability mechanism, which explains why both control strategies are highly efficient. Angled pulsed vortex generator jets with large jet velocities were found to introduce streamwise vortices and to result in earlier transition. Although the control is highly effective, it is not very efficient, as streamwise vortices are not supported by the flow.

Active Flow Control for NACA 6-Series Airfoil at Re = 64,200

Investigations of an airfoil at low Reynolds number conditions

In this paper, a morphing carbon fibre composite aerofoil concept with an active trailing edge is proposed. This aerofoil features of camber morphing with multiple degrees of freedom. The shape morphing is enabled by an innovative structure driven by an electrical actuation system that uses linear ultrasonic motors (LUSM) with compliant runners, enabling full control of multiple degrees of freedom. The compliant runners also serve as structural components that carry the aerodynamic load and maintain a smooth skin curvature. The morphing structure with compliant truss is shown to exhibit a satisfactory flexibility and loading capacity in both numerical simulations and static loading tests. This design is capable of providing a pitching moment control independent of lift and higher L/D ratios within a wider angle-of-attack range. Such multiple morphing configurations could expand the flight envelope of future unmanned aerial vehicles. A small prototype is built to illustrate the concept, but as no off-the-shelf LUSMs can be integrated into this benchtop model, two servos are employed as actuators, providing two controlled degrees of freedom.

https://www.research.manchester.ac.uk/portal/files/52131313/A_morphing_Aerofoil_with_Highly_Controllable_Aerodynamic_Performance_2015_RW_CS_SZ_AF_Final_submission.pdf

A morphing aerofoil with highly controllable aerodynamic performance

Meaningful scaled model flight research requires models that are dynamically and aerodynamically scaled. While dynamic scaling assures that the flight dynamics scale (such as turn rates etc.), aerodynamic scaling assures that the scaled airplane, especially the airfoil, has the same aerodynamic properties (such as aerodynamic coefficients, derivatives, stall behavior etc.) as the full size airplane or airfoil despite the change in Reynolds number associated with the change in length scales, air speeds, and air properties. The present study is concerned with the Aeromot 200S Super Ximango motor glider for which a dynamically scaled 1:5 scale model was built. We investigated aerodynamic scaling for a two-dimensional section of its wing which has a modified NACA 643-618 geometry. For this airfoil, wind tunnel data and airfoil analysis code predictions were found to change noticeably when going from the full size cruise to the model cruise conditions. We investigated two different approaches for obtaining aerodynamic similarity between the 1:5 scale and the full size airfoil at cruise conditions: i) Forced transition with a trip wire and ii) modifying the airfoil geometry.

Aerodynamic Scaling of General Aviation Airfoil for Low Reynolds Number Application

Within the framework of a NASA STTR program, we designed and developed a 1/5 dynamically scaled model of the Aeromot (AMT) 200S motor glider (“SuperXimango”). This model is one element in a “tool box” for scaled model flight research that also includes wind/water tunnel experiments, aerodynamic design tools, and computational fluid dynamics. This 1/5 dynamically scaled model of the Aeromot 200S SuperXimango is awaiting flight testing which will allow for a validation and verification of the scaling by comparison with full scale flight test data. An important criterion in the design and development of the flight model is its ability to serve as a versatile platform for developing and testing of novel technologies. Therefore, great emphasis was placed on a modular design and construction so that certain modules can be easily exchanged.

Benjamin Heine

Papers

Experimental Investigation of Separation and Separation Control on a Laminar Airfoil

Aerodynamic Scaling of General Aviation Airfoil for Low Reynolds Number Application

1/5 scale model of aeromot 200S SuperXimango for scaled flight research