Effectiveness of Large-Camber Circular Arc Airfoil at Very Low Reynolds Numbers

2022

JFST

Self Cite

Since the beginning of space exploration, humans have explored Mars many times in an attempt to understand the origin of life. However, since rovers have been the main means of exploration in the past, only a limited number of areas have been explored. NASA has successfully flown the Mars helicopter 'Ingenuity' for a few minutes on Mars during the 2020 exploration mission (Dutta et al., 2022;Balaram et al., 2018), which helps extend the mission capabilities or the exploration area. JAXA is also planning to launch a fixed-wing unmanned aircraft for Mars exploration in the future of the surface of Mars in detail.Unmanned Mars exploration aircrafts will fly at low Reynolds numbers because the air density on Mars is 1/100 of that on Earth. Therefore, it is necessary to design an airfoil that has high aerodynamic performance at low Reynolds numbers. In the low Reynolds number region, the influence of the viscous force is more dominant than that of the inertial force. Laminar separation bubbles are a typical phenomenon in low Reynolds number flow (Rinoie, 2003). Since the flow velocity is relatively slow in low Reynolds number flow, the boundary layer is laminar. After the laminar boundary layer is separated, a transition to turbulence occurs in the shear layer, and the flows may reattach to the surface. The separated area between the laminar flow separation location and the reattachment location is called the laminar separation bubble. It is known that there are two types of laminar separation bubbles generated on the upper surface of the airfoil: short bubbles and long bubbles. A separation bubble that moves toward the leading edge while shortening the separated region as the angle of attack increases is called a short bubble. Conversely, when the separated region is extended toward the trailing edge, or the reattachment location moves toward the trailing edge as the angle of attack increases, it is called a long bubble. There is a big difference in the pressure distribution between these two types of laminar separation bubbles.An example of research dealing with laminar separation bubbles using the Computational Fluid Dynamics (CFD)

mentioning

confidence: 89%

Section: Comparison Of Aerodynamic Coefficientsmentioning

confidence: 99%

Aerodynamic study of a circular arc airfoil at low Reynolds numbers using Cartesian mesh CFD

TAKASE

2022

JFST

Self Cite

“…A thin circular arc airfoil with a 6% camber (Airfoil 2) was chosen to show the best performance at the Reynolds number studied. 16) Airfoil 1 and Airfoil 2 have thicknesses that were 1.25% and 0.75% of their chord length, respectively. These models were made from a thin aluminum plate.…”

Section: Wind Tunnelmentioning

confidence: 99%

Measurement of Unsteady Aerodynamic Characteristics of a Heaving Wing in a Low Reynolds Number Flow

Fukatsu

Trans. Japan Soc. Aero. S Sci.

2021

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The objective of this study is to determine the two-dimensional unsteady aerodynamic forces and moment acting on a heaving wing in a uniform flow using a wind tunnel. However, it is difficult to measure the aerodynamic forces acting on the heaving wing due to measuring device oscillation and the large inertial force of the wing model. In this study, a new type of wind tunnel test, named ''heaving wind tunnel,'' was developed. Here, the wing model remains stationary as the wind tunnel oscillates with a heaving motion. The advantage of this experimental method is that the measurement results are unaffected by the large inertial force acting on the oscillating wing model. Therefore, the wing model can be used in the same way as in steady state experiments. The normal force, thrust and pitching moment coefficients of a heaving airfoil were measured using the heaving wind tunnel test developed in this study. Through flow visualizations and pressure measurements, we found that the rapid drop in normal force coefficient after it reached its maximum value was due to a large growing leading-edge vortex.

“…Several groups, such as Okamoto et al, 4) Azuma et al, 5) Kesel, 6) Sunada et al, 7) Obata and Shinohara, 8) Shi et al 9) and Okamoto and Ebina, 10) have investigated the twodimensional characteristics of steady wings experimentally (at Re 1 Â 10 4 ) using both wind tunnel and water tank tests. These studies arrived at the following conclusions: i) Effective airfoils designed for low Reynolds numbers are thin, have a sharp leading-edge, and a corrugated profile, similar to the dragonfly wing.…”

Section: Introductionmentioning

confidence: 99%

Disappearance of Vortex Lift in Low-Aspect-Ratio Wings at Very-low Reynolds Numbers

Trans. Japan Soc. Aero. S Sci.

Kamikubo

et al. 2019

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The objective of this study is to ascertain the aerodynamic characteristics of low-aspect-ratio wings at Reynolds numbers ranging between 1©10 3 and 1©10 4 which correspond to insect wings. The wings tested in this study are rectangular, thin, flat plates with aspect ratios varying from 0.5 to 2. The very small forces and moment acting on the wings were measured using a low-pressure wind tunnel. Although a large maximum lift coefficient was obtained for the wing with an aspect ratio of 1 at a Reynolds number of 1©10 4 , it decreased as the Reynolds number decreased due to the disappearance of vortex lift. That is, the Reynolds number effects of low-aspect-ratio wings were found at the current Reynolds number. However, as the aspect ratio of the wing changed, the rate at which the maximum lift coefficient decreased was reduced. The main cause of the phenomenon was the behavior of the wing-tip vortices. These aerodynamic characteristics of wings will be important for developing insect-sized aircraft.