A Micro air vehicle (MAV) is defined as class of unmanned air vehicle (UAV) having a linear dimension of less than 15 centimeters and a mass of less than 100 grams with flight speeds of 6 to 12 meters per second. MAVs fall within a Reynolds number (Re) range of 50,000 and 120,000, in which many causes of unsteady aerodynamic effects are not fully understood. The research field of low Reynolds number aerodynamics is currently an active one, with many defence organizations, universities, and corporations working towards a better understanding of the physical processes of this aerodynamic regime. In the present work, it is proposed to study the unsteady aerodynamic analysis of 2D airfoil using CFD software and Xfoil panel code method. The various steps involved in this work are geometric modelling using CATIA V5R17, meshing using ICEM CFD, and solution and postprocessing through FLUENT. The finite control volume analysis and Xfoil panel code method has been carried out to predict aerodynamic characteristics such as lift coefficients, drag coefficients, moment coefficients, pressure coefficients, and flow visualization. The lift and drag coefficients were compared for all the simulations with experimental results. It was observed that for the 2D airfoil, lift and drag both compared well for the midrange angle of attack from −10 to 15 degree AOA.

Micro air vehicles (MAVs) have attracted significant attention since mid-1990 for both civilian and military applications. Micro air vehicle (MAV) is defined here as a small, portable flying vehicle which is designed for performing useful work. The desire for portable, low altitude aerial surveillance has driven the development of aircraft on the scale of small birds. Vehicles in this class of small-scale aircraft are known as

MAVs are by definition small aircrafts which fly at relatively low speeds. Such flight characteristics will result in flow regimes with Reynolds numbers. Another aerodynamic signature of MAV is wings with small aspect ratio; in most cases the chord is roughly equal to the wingspan. This combination of low Reynolds number flight and low aspect ratio wings results in a flow regime totally alien to conventional aircraft. Although small birds and insects have been flying under these conditions for quite some time (Figure

Conventions and terminology. Sketch of an insect [

In order for required MAV capabilities to be realized, several areas will need more focused attention. The absence of sophisticated computational analysis methods, lack of commercially available micro electromechanical sensors, and the difficulties associated with accurate experimental work at this scale have all restricted research. From a system and manufacturing standpoint, technological advances in micro fabrication techniques and in the miniaturization of electronics in the last decade made mechanical MAVs feasible. Key research challenges include unsteady aerodynamics at low Reynolds number, low aspect ratio wings, stability and control issues associated with low weight, small moments of inertia, miniaturization, cooperative control, and micro sensors. Among these areas unsteady aerodynamics is an important area of research.

Unsteady aerodynamics plays a significant role in MAV flight and stability. Unsteady phenomena may arise due to natural time dependent changes in the flow itself or it may be created by changes in the position or orientation of a body. In many unsteady flows of interest, the important unsteady aspects involve not only the kinematic changes in boundary conditions caused by the motion of a body but also the influence of an unsteady wake and the changes in the pressure-velocity relationship associated with the unsteady form of Bernoulli’s equation [

Below is given a 2D linear translation of a wing of an airfoil (Figure

Airfoil nomenclatures.

A 2D linear translation, (Figure

2D linear translations [

Mechanisms such as rotational circulation, wake capture, and the unsteady leading edge vortex do seem to properly account for the aerodynamics forces. Regarding forward flight, the unsteady leading edge vortex is the only mechanism present to produce the necessary forces. The unsteady leading edge vortex involves leading edge flow separation that reattaches to the wing and forms a separation bubble. The vortex increases the circulation around the wing and creates much higher lift than the steady-state case. This vortex remains stable due to its highly three-dimensional nature.

Low Reynolds numbers make the problem of airfoil design difficult because the boundary layer is much less capable of handling an adverse pressure gradient without separation. Thus, very low Reynolds number designs do not have severe pressure gradients and the maximum lift capability is restricted. At very low Reynolds numbers, most or all of the boundary layer is laminar. Laminar separation bubbles are common and unless properly stabilized can lead to excessive drag and low maximum lift [

The focus of the proposed study is to determine the characteristics of unsteady aerodynamics of 2D airfoil at different angle of attack during operation and to achieve at an optimum result against the experimental and existing literature results. The rigorous work involves the modeling and analysis of the entire fixed wing MAV 2D airfoil using CATIA, ANSYS FLUENT, and ICEM-CFD. Various angle of attack 2D airfoil characteristics such as pressure distribution, lift coefficient, drag coefficient, and moment coefficient over the fixed wing MAV 2D airfoil at different flight conditions will be studied and an optimum configuration will be suggested for safe operations. The following governing equations are the prime drivers for the computation of the aerodynamic characteristics.

The flow chart in Figure

Analysis procedure and the components.

The standard procedure for ANSYS FLUENT work follows the above components. For the present work, in this case to ensure that 2D, later this mesh file is imported into ANSYS FLUENT for analysis. In the FLUENT, the analysis will be carried out. The postprocessing is carried according to the requirements.

The physical characteristics of selected airfoil such as thickness 0.09996, camber 0.03503, and area 0.05972. The purpose of choosing this specific airfoil is low Reynolds number (Re) which gives better aerodynamic characteristic performance as compared to the other airfoils and it is the one of the best airfoils which is used in design of micro aerial vehicle [

In this study only the 2D airfoil is considered. A schematic geometry of the wing is shown in Figure

Geometry details of 2D airfoil.

The physical problem under consideration is the flow over an airfoil in a computational domain as shown in Figure

Computational domain.

The basic requirement of the airfoil location is to make the outer boundaries sufficiently far away from the airfoil so that they do not have much impact on the computed results; the relative position of the airfoil is shown in Figure

The computational model is created in ICEM-CFD as per the dimensions shown in Figure

Grid distributions around the 2D airfoil.

The grid distribution around the wing is shown in Figure

The FLUENT setup for 2D airfoil includes solvers settings, operating conditions, boundary conditions, and reference values. In this work the pressure, density, and temperature are taken to be constant for sea level conditions because of laminar flow. The velocity taken 11.5 m/s is maximum velocity of the designed micro aerial vehicle [

Histogram of angle.

In this section, the force coefficients are computed for the wing for different AOA at 11.5 m/s speed using fluent software. Figure

Lift coefficients versus AOA.

At an AOA,

Figure

Drag coefficients versus AOA.

As AOA is increased beyond 15°, massive separation occurs on most of the upper surface, the lift decreases, and drag starts to increases as seen in the Figure

In this section, the force coefficients are computed for the wing for different AOA at 11.5 m/s speed using Xfoil panel code method. Figure

Lift coefficients versus AOA.

At an AOA,

At AOA of 10^{0}, the flow on the upper surface starts to get separated from a large portion of the surface; however, the lift forces sometimes may increase with the AOA. The reason might be tip vortices suction near tip area which would result in additional lift or the flow from the high pressure region on the lower wing surface tries to reach the low pressure region on the upper wing surface.

Figure

Drag coefficients versus AOA.

As AOA is increased beyond 15°, massive separation occurs on most of the upper surface, the lift decreases, and drag starts to increase as seen in the Figure

Figures

Contours of pressure efficient −10° through +15° of AOA.

−10° AOA

−5° AOA

0° AOA

5° AOA

10° AOA

15° AOA

Figures

Lift coefficients versus AOA.

Figure

Figure

Drag coefficients versus AOA.

Lift coefficients versus drag coefficients.

Figure

The following conclusions can be made from the 2D airfoil study.

It is observed from the Figures

The coefficient of lift versus angle of attack for the FX60100 2D airfoil and the plot show very good correlation between the two different solvers results as well as the experimental data obtained from the literature-1.

The coefficient of drag is high in FLUENT results as compared to the Xfoil and experimental data obtained from the literature-1. The exact drag prediction is highly difficult.

The study of the 2D airfoil Wortmann FX 60100 shows a good agreement between the results of CFD analysis with the reference values [

A major reason for the CFD coefficient of moment analysis was not to study but to verify the data obtained from the wind tunnel tests. Also none of the airfoils and models tested had a coefficient of moment data.

The author declares that there is no conflict of interests regarding the publication of this paper.