Pitching moment

About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.

Aerodynamic Scaling of General Aviation Airfoil for Low Reynolds Number Application

Abstract: 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.

Numerical Studies of the Jet Interaction Flowfield with a Main Jet and an Array of Smaller Jets

Abstract: During the present numerical study the jet interaction flowfield associated with the sonic injection of a gas into a high speed crossflow was simulated using the Reynolds Averaged Navier Stokes (RANS) equations. Turbulence was modeled using Wilcox's 1988 k-ω turbulence model. The computations made use of the finite volume GASP Version 4. Calculations were run for a number of jet interaction configurations consisting of a primary jet alone, a primary jet and one pair of secondary jets, and a primary jet and two pairs of secondary jets. Two flow conditions were considered: one with a Mach number of 2.4 and a pressure ratio of 14 and the other with a Mach number of 4.0 and a pressure ratio of 532. The numerical solutions were compared to the experimental results of the corresponding jet interaction tests run at Virginia Tech in order to assess the capability of RANS and of first- order turbulence models to properly simulate the complex flowfield. The k-ω turbulence model proved to be reliable and robust, and the results it provided for this type of flowfield were accurate enough from an engineering standpoint to make informed decisions about the configuration layout. In spite of the overall good performance, the k-ω turbulence model failed to correctly predict the flow in the regions of strong adverse pressure gradients. Comparisons with experimental results showed that the separation region was often under-predicted thus highlighting the need to employ second-order turbulence models. The RANS simulations was found accurate enough to provide physical mean-flow solutions. A large effort was dedicated to the development of an efficient computational grid that could capture most of the flow- physics with the least amount of cells. To this end Chimera or overset grids were employed in the simulation of the secondary injectors. The simulations showed that the innovative configuration with one primary jet and an array of smaller secondary jets effectively decrease the nose-down pitching moment by as much as 160%. In some cases it also increased the total normal force acting on the flat plate (namely the thrust) by as much as 3%. This effect was found to be caused by the reduction in size and intensity of the low- pressure region aft of the primary injector.

Nondimensional Modeling of Ducted-Fan Aerodynamics

Abstract: The unique aerodynamic nature of the ducted-fan configuration makes it difficult to represent in terms of traditional nondimensional coefficients. Analysis of wind-tunnel data for an axisymmetric generic ducted-fan configuration has led to a new nondimensional modeling scheme. Force coefficients are plotted versus advance ratio for a range of angles of attack, yielding several observations. Each angle of attack yields a linear trend versus advance ratio, with all lines converging through a single point. This fulcrum point shares the same thrust coefficient value as hover tests but at a nonzero advance ratio. This suggests that a hovering ducted fan self-induces a freestream flow, even though the vehicle is stationary. The complicated pitching moment behavior is captured succinctly through modeling the center of pressuremovement. The fan power required was also successfully modeled using the figure of merit, typically a hover performance metric, over the entire flight regime to relate power required to thrust generated. A new wind-tunnel velocity correction for ducted fans is also presented. The new statistical modeling technique attains very high correlation for present and legacy data. It is possibly the most concise representation of ducted-fan aerodynamics to date, using 12 nondimensional coefficients.

Aerodynamic Limitations of the UH-60A Rotor

Abstract: High quality airloads data have been obtained on an instrumented UH-60A in flight and these data provide insight into the aerodynamic limiting behavior of the rotor. At moderate weight coefficients and high advance ratio limiting performance is largely caused by high drag near the blade tip on the advancing side of the rotor as supercritical flow develops on the rotor with moderate to strong, shocks on both surfaces of the blade. Drag divergence data from two-dimensional airfoil tests show good agreement with the development of the supercritical flow regions. Large aerodynamic pitching moments are observed at high advance ratio, as well, and these pitching moments are the source of high torsional moments on the blade and control system loads. These loads occur on the advancing side of the disk and are not related to blade stall which does not occur for these weight coefficients. At high weight coefficients aerodynamic and structural limits are related to dynamic stall cycles that begin on the retreating side of the blade and, for the most severe conditions, carry around to the advancing side of the blade at the presumed first frequency of the blade/control system.

Navier-Stokes analysis of airfoils with Gurney flap

Abstract: Two dimensional steady state Navier-Stokes computations were performed to determine the effect of Gurney flap on NACA 4412 and NACA 0011 airfoils. Gurney flap sizes selected for the study range from 0.5% to 4% of the airfoil chord. A compressible Navier-Stokes solver with Baldwin-Lomax turbulence model, JUMBO2D, is used to predict the flow field around the airfoils. Computed results have been compared with available experimental and computational data. There is good correlation observed between computed and experimental data. Addition of Gurney flap increases the lift coefficient significantly with very little drag penalty if proper Gurney flap height is selected. Nose down pitching moment also increases with Gurney flap height. Flow field structure near the trailing edge shows very good resemblance with Liebeckx2019;s hypothesis that provides the possible explanation for the increased aerodynamic performance