The two dimensional flow of an oscillating SC1095 airfoil with Co-Flow Jet (CFJ) flow control is simulated using Unsteady Reynolds Average Navier-Stokes (URANS). A 5th order WENO scheme for the inviscid flux, a 4th order central differencing model for the viscous terms and the one equation Spalart-Allmaras model for the turbulence are used to resolve the flow. The Mach number is 0.3 and Reynolds number is 3.93× 10 at reduced frequency from 0.05 to 0.2. The simulated results for the baseline agree reasonably well with the experiments for no-stall, mild-stall and deep-stall cases. The CFJ pitching airfoil is found to increase the airfoil performance for every flow studied. At Cμ = 0.08 the lift is increased by 32% and the drag is decrease by 80%. Considering only the aerodynamic forces applied on the airfoil and not the pumping power, (L/D)ave for this case reach an outstanding 118.3. When Cμ is increased, the average drag becomes negative, proving the feasibility of a CFJ helicopter blade using its pump as the only source of power. Due to the removal of dynamic stall, CFJ airfoil is able to remove the sharp moment drop at high angle of attack. Nomenclature CFJ Co-flow jet AoA Angle of attack LE Leading Edge TE Trailing Edge ZNMF Zero-net mass-flux S Planform area c Profile chord U Flow velocity q Dynamic pressure 0.5 ρU p Static pressure ρ Air density ω Angular velocity of oscillation ṁ Mass flow M Mach number ∞ Free stream conditions j Jet conditions α0 Mean angle of attack ∗ Graduate Student, AIAA Member † Associate Professor, AIAA Senior Member

Numerical simulation of pitching airfoil performance enhancement using Co-Flow Jet Flow control

To assess their application to rotorcraft, the two-dimensional aerodynamics of deployable Gurney flaps, referred to as miniature trailing-edge effectors, are explored using computational fluid dynamics. These deployable devices have a height of only a few percent of the airfoil chord and deploy normal to the airfoil surface near the trailing edge. Their small size, low inertia, and small added mass make them well suited for deployment in high-frequency applications such as those needed for rotorcraft. A combination of wind-tunnel measurements using airfoils fitted with Gurney flaps and unsteady circulatory theory are used to validate the computational fluid dynamics, and grid and time-resolution studies are used for code verification. Qualitative and quantitative agreement of the effects of a Gurney flap with experiments and theory suggest that the computational fluid dynamics results are valid. These investigations examine the effects of the chordwise positioning and deployment frequency of the miniature trailing-edge effectors. In doing so, their operation on both static and dynamically pitching airfoils is considered. Through these studies, a number of physical insights into miniature trailing-edge effectors and Gurney flap aerodynamics have been obtained. These insights have led to the introduction of a scaling parameter that easily accounts for compressibility effects, an understanding of the aerodynamic consequences due to positioning miniature trailing-edge effectors upstream of the trailing edge, and an assessment on the benefits of using of miniature trailing-edge effectors for active stall alleviation on an airfoil oscillating in pitch.

Numerical Investigation on the Aerodynamics of Oscillating Airfoils with Deployable Gurney Flaps

Energy harvesting properties of a flapping wing with an adaptive Gurney flap

The impact of Gurney flaps (GF), of different heights and perforations, on the aerodynamic and wake characteristics of a NACA 0015 airfoil equipped with a trailing-edge flap (TEF) was investigated experimentally at Re = 2.54 × 105. The addition of the Gurney flap to the TEF produced a further increase in the downward turning of the mean flow (increased aft camber), leading to a significant increase in the lift, drag, and pitching moment compared to that produced by independently deployed TEF or GF. The maximum lift increased with flap height, with the maximum lift-enhancement effectiveness exhibited at the smallest flap height. The near wake behind the joint TEF and GF became wider and had a larger velocity deficit and fluctuations compared to independent GF and TEF deployment. The Gurney flap perforation had only a minor impact on the wake and aerodynamics characteristics compared to TEF with a solid GF. The rapid rise in lift generation of the joint TEF and GF application, compared to conventional TEF deployment, could provide an improved off-design high-lift device during landing and takeoff.

Lift enhancement and flow structure of airfoil with joint trailing-edge flap and Gurney flap

The effect of structural and aerodynamic uncertainties on the performance predictions of a helicopter is investigated. An aerodynamic model based on blade element and momentum theory is used to predict the helicopter performance. The aeroelastic parameters, such as blade chord, rotor radius, two-dimensional lift-curve slope, blade profile drag coefficient, rotor angular velocity, blade pitch angle, and blade twist rate per radius of the rotor, are considered as random variables. The propagation of these uncertainties to the performance parameters, such as thrust coefficient and power coefficient, are studied using Monte Carlo Simulations. The simulations are performed with 100,000 samples of structural and aerodynamic uncertain variables with a coefficient of variation ranging from 1 to 5%. The scatter in power predictions in hover, axial climb, and forward flight for the untwisted and linearly twisted blades is studied. It is found that about 20-25% excess power can be required by the helicopter relative to the determination predictions due to uncertainties.

Uncertainty Quantification in Helicopter Performance Using Monte Carlo Simulations

In the present study, the aerodynamic characteristics of the Gurney flap were comprehensively investigated in terms of the performance requirements for a helicopter rotor by using two-dimensional Navier-Stokes equations. To this end, with the rotor operating flow conditions in mind, the static aerodynamic characteristics of the Gurney flap are thoroughly compared with those of the clean airfoil at various Mach numbers, incidences, and Gurney flap heights. Next, to understand the general dynamic stall features of the airfoils with the Gurney flap, a series of parametric studies are performed with respect to oscillating frequency and amplitude, and the correlations of the aerodynamic coefficients are obtained by using the dynamic stall function of Bousman. It is concluded that there exists some optimum Gurney flap heights, which minimize the drag and pitching moment while maximizing the lift coefficient and lift-to-drag ratio at the same time. In the present study, the 2% Gurney flap would be a good compromise to satisfy all the major rotorcraft design criteria.

Wandon Joo

Papers

Aerodynamic Performance Analysis of a Gurney Flap for Rotorcraft Application