Pitching moment

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

Performance Measurements of an Airfoil at Low Reynolds Numbers

Abstract: Performance characteristics of an Eppler 387 airfoil using both direct (force) and indirect (pressure) measurement techniques have been obtained at Reynolds numbers from 60,000 to 460,000 in the Langley Low-Turbulence Pressure Tunnel. Lift, drag, and pitching-moment data were obtained from two internally-mounted strain-gage balances specifically designed for small aerodynamic loads. Comparisons of these results with data from a pressure model of an Eppler 387 airfoil are included. Drag data for both models using the wake traverse method are compared with the balance data. Oil flow visualization and surface mounted hot-film sensors were used to determine laminar-separation and turbulent-reattachment locations. Problems associated with obtaining accurate wind-tunnel data at low Reynolds numbers are discussed.

An Approximate Method for the Calculation of Nonstationary Air Forces at Subsonic Speeds

Abstract: : The present report explains and illustrates a method of computing the non-stationary forces and moments on an oscillating airfoil at subsonic speeds. The process is based on the well known Possio integral equation relating the pressure on the airfoil to the normal velocity. Part I of the report contains the theoretical development which leads to the required equations for determining the lift and moment. In Part II the method of Part I is applied to the computation of the aerodynamic lift and moment coefficients for four principal degrees of freedom of the airfoil.

Aerodynamic Design of Transonic Natural-Laminar-Flow (NLF) Wing via Surrogate-basedGlobal Optimization

Abstract: This paper aims to develop an efficient global optimization method for design of transonic natural-laminar-flow (NLF) airfoils and wings, based on high-fidelity computational fluid dynamics (CFD) solver. The CFD solver features functionality of automatic transition prediction, by coupling Reynolds-averaged Navier-Stokes (RANS) equations with the linear-stability-theory-based dual e N method for Tollmien-Schlichting and crossflow instabilities. An A320-sized transonic NLF wing with a laminar supercritical airfoil is designed for cruise condition at Mach=0.74, Re=20 million, CL=0.515. In order to further improve the cruise efficiency, this NLF wing is optimized at higher Mach number of 0.75 via an in-house surrogate-based optimizer. The optimization is formulated as a drag minimization problem with constraints on lift, pitching moment and geometric thickness. Through only 130 CFD evaluations, 12.1 counts drag reduction is obtained, while all constraints are strictly satisfied. Further study shows that the drag reduction is contributed by both of shock-wave weakening and laminar-flow extension. On suction side, the favorable pressure gradient is maintained while shock wave is weakened; on pressure side, the crossflow (CF) instability is effectively suppressed and thereby the laminar flow region is dramatically extended. The improvement of aerodynamic performance is observed not only at design point but also over a certain range of off-design lift coefficients.

Soft Computing Based Force Recovery Technique for Hypersonic Shock Tunnel Tests

Abstract: A hemispherical model equipped with a three component accelerometer force balance has been tested in a shock tunnel at Mach 8.0 freestream conditions. A novel technique has been devised using the Artificial Neuro-Fuzzy Inference System (ANFIS) for recovering the forces experienced by the model during the experiments. Implementation of this methodology in calibration of the force balance showed encouraging agreement with the impulse forces recovered from the calibration tests. The same recovery procedure is then adopted to obtain the time history of the forces for 0∘ and 15∘ angle of attack experiments. The drag recovered in steady state is found to agree well with the conventional methods with minor discrimination for the lift and pitching moment. In light of the limitation of the accelerometer force balance theory due to the unaccountability of model dynamics, the force recovery technique proposed herein is found simple to implement and can be opted as a tool for prediction of the aerodynamic coefficient...

Errata and Addenda to "Application of Oscillatory Aerodynamic Theory to Estimation of Dynamic Stability Derivatives"

Abstract: T pitching moment coefficients in Ref. 1 are referred to an axis through the wing apex with the pitch axis through the quarter-chord point of the mean aerodynamic chord (MAC). It was the authors' intention to present the coefficients using the same reference and pitch axes at the quarterchord point of the MAC. The example wing had an aspect ratio of 8.0, a taper ratio of 0.25, a quarter-chord sweep of 30 deg., and was flying at a Mach number of 0.8. Using a new lattice idealization of the wing (since the original idealization was not recorded) defined by 5 equal chordwise divisions and 15 variable spanwise (narrower toward the tip) divisions, the new lift and corrected moment coefficients for the quarterchord MAC reference axis and pitch axis are presented in Table 1 for the nine values of reduced frequency previously considered. The calculations were based on the doublet-lattice method (DLM) of Ref. 2 as integrated into NASTRAN® and were carried out using MSC/NASTRAN; the original calculations were based on the DLM of Ref. 4 which was later developed into Ref. 5. Slight differences in the lift coefficients between the present and earlier solutions can be attributed to a different lattice idealization. If we extend Ref. 1 to permit different reference chords for reduced frequency (k = ub/V) and pitching moment coefficient