scholarly journals An Improved Nonlinear Aerodynamic Derivative Model of Aircraft at High Angles of Attack

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Mi Baigang ◽  
Yu Jingyi
Keyword(s):  
Oscillation Amplitude ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Higher Order ◽  
Initial Angle ◽  
Prediction Ability ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
High Angles Of Attack ◽  
Nonlinear Aerodynamic

The classical aerodynamic derivative model is widely used in flight dynamics, but its application is extremely limited in cases with complicated nonlinear flows, especially at high angles of attack. A modified nonlinear aerodynamic derivative model for predicting unsteady aerodynamic forces and moments at a high angle of attack is developed in this study. We first extend the higher-order terms to describe the nonlinear characteristics and then introduce three more influence parameters, the initial angle of attack, the reduced frequency, and the oscillation amplitude, to correct the constant aerodynamic derivative terms that have higher-order polynomials for these values. The improved nonlinear aerodynamic derivative model was validated by using the NACA 0015 airfoil and the F-18 model. The results show that the improved model has a higher prediction ability at high angles of attack and has the ability to predict the aerodynamic characteristics of other unknown states based on known unsteady aerodynamic data, such as the initial angle of attack, reduced frequency, and oscillation amplitude.

Comparison of the Unsteady Loads of an Airfoil in the Pitching and Plunging Motions

2006 ◽  
Author(s):  
M. Soltani ◽  
M. Seddighi ◽  
F. Rasi
Keyword(s):  
Subsonic Flow ◽  
Free Stream ◽  
Incident Angle ◽  
Oscillation Amplitude ◽  
Stream Velocity ◽  
Frequency Oscillation ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Series Of Experiments

A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of motion on the unsteady aerodynamic loads of the airfoil at pre-stall, near stall, and post stall conditions. Variations of the aerodynamic coefficients with equivalent angle of attack for both pitching and plunging motions showed strong sensitivity to the reduced frequency, oscillation amplitude, Reynolds number, and mean angles of attack.

Unsteady aerodynamic characteristics of a morphing wing

2018 ◽  
Vol 91 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Jinwu Xiang ◽  
Kai Liu ◽  
Daochun Li ◽  
Chunxiao Cheng ◽  
Enlai Sha
Keyword(s):  
Lift Coefficient ◽  
Angle Of Attack ◽  
Large Angle ◽  
Unsteady Aerodynamics ◽  
Aerodynamic Characteristics ◽  
Static Case ◽  
Morphing Wing ◽  
Trailing Edge ◽  
Content Type ◽  
Unsteady Aerodynamic

Purpose The purpose of this paper is to investigate the unsteady aerodynamic characteristics in the deflection process of a morphing wing with flexible trailing edge, which is based on time-accurate solutions. The dynamic effect of deflection process on the aerodynamics of morphing wing was studied. Design/methodology/approach The computational fluid dynamic method and dynamic mesh combined with user-defined functions were used to simulate the continuous morphing of the flexible trailing edge. The steady aerodynamic characteristics of the morphing deflection and the conventional deflection were studied first. Then, the unsteady aerodynamic characteristics of the morphing wing were investigated as the trailing edge deflects at different rates. Findings The numerical results show that the transient lift coefficient in the deflection process is higher than that of the static case one in large angle of attack. The larger the deflection frequency is, the higher the transient lift coefficient will become. However, the situations are contrary in a small angle of attack. The periodic morphing of the trailing edge with small amplitude and high frequency can increase the lift coefficient after the stall angle. Practical implications The investigation can afford accurate aerodynamic information for the design of aircraft with the morphing wing technology, which has significant advantages in aerodynamic efficiency and control performance. Originality/value The dynamic effects of the deflection process of the morphing trailing edge on aerodynamics were studied. Furthermore, time-accurate solutions can fully explore the unsteady aerodynamics and pressure distribution of the morphing wing.

scholarly journals Unsteady Force Measurements on Fully Wetted Hydrofoils in Heaving Motion

1968 ◽  
Vol 12 (01) ◽  
pp. 69-80
Author(s):  
G. J. Klose ◽  
A. J. Acosta
Keyword(s):  
Theoretical Calculations ◽  
Oscillation Amplitude ◽  
Angle Of Attack ◽  
Two Dimensional ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Reduced Frequency ◽  
Unsteady Force ◽  
Two Dimensional Flow ◽  
Submergence Depth

An experimental investigation is reported of the unsteady forces due to heaving motion of fully wetted hydrofoils of unity aspect ratio and also in two-dimensional flow. The tests covered a broad range of reduced frequency and determined the effects of variation in submergence depth, angle of attack, oscillation amplitude, and flow velocity. In general, the findings agree well with available theoretical calculations, but some unexpected variations were found for the case of a wedge-shaped foil and for changes in angle of attack.

Modeling of unsteady aerodynamic characteristics at high angles of attack

2018 ◽  
Vol 233 (6) ◽  
pp. 2291-2301 ◽  
Author(s):  
Dong Hao ◽  
Lin Zhang ◽  
Jing Yu ◽  
Daiyong Mao
Keyword(s):  
State Space ◽  
Series Expansion ◽  
Angular Rate ◽  
Minimum Mean Square Error ◽  
Aerodynamic Characteristics ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Model ◽  
Constant Pitch ◽  
High Angles Of Attack ◽  
Taylor’S Series

An improved model to express the unsteady aerodynamic characteristics at high angles of attack is presented in this paper. The proposed aerodynamic model is expressed on the basis of a progressive state-space representation and Taylor’s series expansion. The state-space expression is a first-order differential equation in which the power item of the angular rate of attack is introduced. The unsteady aerodynamic coefficients are described by Taylor’s series expansion in terms of input variables. The approach of minimum mean square error criterion is utilized to identify the unknown parameters of the proposed model by nonlinear least square method from the tunnel data. The given modeling method is experimentally demonstrated by the wind tunnel measurements of NACA 0015 airfoil with constant rate to high angles of attack, F18 aircraft with constant pitch rate ramp motion, and F18 HARV (high alpha research vehicle) configuration with large-amplitude harmonic oscillatory. The results show that it is possible to analyze more complex unsteady aerodynamic problems for an aircraft within the framework of the proposed aerodynamic model and the represented model is directly amenable to the simulation and control system design.

scholarly journals Effects of Pitching Motion Elements on Aerodynamic Characteristics of Airfoil

2021 ◽  
Vol 2076 (1) ◽  
pp. 012078
Author(s):  
Rui Yin ◽  
Jing Huang ◽  
Zhi-Yuan He
Keyword(s):  
Drag Coefficient ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Initial Angle ◽  
Pitching Motion ◽  
The Difference ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

Abstract The aerodynamic characteristics of NACA4412 airfoil with different pitching motion elements were compared and analyzed based on CFD in this research. The results are acquired as follows: the difference between the lift and drag coefficients of the airfoil during pitch up and pitch down motions becomes larger with the increase of the pitching amplitude or initial angle of attack; as the pitching amplitude increases, the lift coefficient grows slightly greater and the drag coefficient grows much greater; as the initial angle of attack increases, the lift coefficient grows much greater and the drag coefficient grows slightly; the smaller the attenuation frequency is, the larger the lift-to-drag ratio of the airfoil will be.

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