INVESTIGATION OF SUITABILITY FOR THE LINEAR SUPERPOSITION MODEL

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1631-1634
Author(s):  
DA HUANG ◽  
GENXIN WU
Keyword(s):  
Angle Of Attack ◽  
Large Angle ◽  
Unsteady Aerodynamics ◽  
Mathematic Model ◽  
Linear Superposition ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Model ◽  
Aerodynamic Parameters ◽  
Principle Of Linear Superposition ◽  
Low Speed Wind Tunnel

An aircraft model was tested at the 3-meter low speed wind tunnel as it was oscillated with large amplitude. The unsteady aerodynamic behavior was acquired during the oscillation in yawing, rolling and yawing-rolling. The lateral-directional dynamic derivative was obtained using the mathematic model of unsteady aerodynamics and the dynamic derivative simulation. According to the principle of linear superposition, the unsteady aerodynamic parameters of the model about yaw-roll coupled motion can be obtained by the quasi-steady aerodynamic model and the result was compared with the experimental test. It was found that for the quasi-steady aerodynamic model the unsteady aerodynamic characteristic was in agreement with the test at the middle and large angle of attack (for example α ≤ 45°), but was opposite at the extremely large angle of attack (α > 45°).

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.

Review of Two Numerical Approaches to Predict Nonlinear Airfoil Response to High-Amplitude Incident Gust

2004 ◽  
Author(s):  
Vladimir V. Golubev
Keyword(s):  
Unsteady Aerodynamics ◽  
High Amplitude ◽  
Finite Amplitude ◽  
Computational Aeroacoustics ◽  
Mean Flow ◽  
Linear Superposition ◽  
Perturbation Field ◽  
Unsteady Aerodynamic ◽  
The Mean ◽  
Numerical Approaches

In this work, two different numerical methods of time-accurate nonlinear analysis are reviewed and compared in application to the problem of nonlinear unsteady aerodynamic and aeroacoustic airfoil responses to a high-intensity impinging gust. The incident perturbation field is of finite amplitude relative to the mean flow so that in general, no assumption of a linear superposition of responses from each individual harmonic can be made. Thus, in addition to providing a comparison of two different approaches in computational aeroacoustics, the paper achieves the objective of obtaining verified solutions determining the limits of validity for linearized methods, universally accepted in studies of unsteady aerodynamics and aeroacoustics. The work investigates nonlinear near- and far-field responses of a Joukowksi airfoil in the parametric space of gust intensity and frequency.

scholarly journals Nonlinear Unsteady Aerodynamics Reduced Order Model of Airfoils Based on Algorithm Fusion and Multifidelity Framework

2021 ◽  
Vol 2021 ◽  
pp. 1-26
Author(s):  
Yan Shi ◽  
Zhiqiang Wan ◽  
Zhigang Wu ◽  
Chao Yang
Keyword(s):  
Data Fusion ◽  
Unsteady Aerodynamics ◽  
Separated Flow ◽  
High Fidelity ◽  
Intelligent Algorithm ◽  
Fusion Algorithm ◽  
Reduced Order ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Model ◽  
Traditional Algorithm

A reduced order modeling method based on algorithm fusion and multifidelity framework for nonlinear unsteady aerodynamics is proposed to obtain a low-cost and high-precision unsteady aerodynamic model. This method integrates the traditional algorithm, intelligent algorithm, and multifidelity data fusion algorithm. In this method, the traditional algorithm is based on separated flow theory, the intelligent algorithm refers to the nonlinear autoregressive (NARX) method, and the multifidelity data fusion algorithm uses different fidelity data for aerodynamic modeling, which can shorten the time cost of data acquisition. In the process of modeling, firstly, a multifidelity model with NARX description provides a general intelligent algorithm framework for unsteady aerodynamics. Then, based on the separated flow theory, the correction equation from low-fidelity model to high-fidelity result is constructed, and the cuckoo algorithm based on chaos optimization is used to identify the parameters. In order to verify the effectiveness of the method, an unsteady aerodynamic model of NACA0012 airfoil is established. Three kinds of data with low, medium, and high fidelity are used for modeling. The low-fidelity and medium-fidelity data is obtained from the CFD-Euler solver and CFD-RANS solver, respectively, while the high-fidelity data comes from the experimental results. Then, the model is established, and its prediction of unsteady aerodynamic coefficients is in good agreement with the CFD results and the experimental data. After that, the model is applied to a two-dimensional aeroelastic system, and the bifurcation and limit cycle response analysis are compared with the experimental results, which further shows that the model can accurately capture the main flow characteristics in the flow range of low speed and high angle of attack. In addition, the convergence of the model is studied; the accuracy and generalization ability as well as applicability scope of the model are compared with other aerodynamic models and finally discussed.

scholarly journals Comparative Study of Different Turbulence Models for Cavitational Flows around NACA0012 Hydrofoil

2021 ◽  
Vol 9 (7) ◽  
pp. 742
Author(s):  
Minsheng Zhao ◽  
Decheng Wan ◽  
Yangyang Gao
Keyword(s):  
Angle Of Attack ◽  
Large Angle ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Specific Information ◽  
Cloud Cavitation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Shedding Frequency ◽  
Reynolds Average

The present work focuses on the comparison of the numerical simulation of sheet/cloud cavitation with the Reynolds Average Navier-Stokes and Large Eddy Simulation(RANS and LES) methods around NACA0012 hydrofoil in water flow. Three kinds of turbulence models—SST k-ω, modified SST k-ω, and Smagorinsky’s model—were used in this paper. The unstable sheet cavity and periodic shedding of the sheet/cloud cavitation were predicted, and the simulation results, namelycavitation shape, shedding frequency, and the lift and the drag coefficients of those three turbulence models, were analyzed and compared with each other. The numerical results above were basically in accordance with experimental ones. It was found that the modified SST k-ω and Smagorinsky turbulence models performed better in the aspects of cavitation shape, shedding frequency, and capturing the unsteady cavitation vortex cluster in the developing and shedding period of the cavitation at the cavitation number σ = 0.8. At a small angle of attack, the modified SST k-ω model was more accurate and practical than the other two models. However, at a large angle of attack, the Smagorinsky model of the LES method was able to give specific information in the cavitation flow field, which RANS method could not give. Further study showed that the vortex structure of the wing is the main cause of cavitation shedding.

The Sears problem for a lifting airfoil revisited - new results

1984 ◽  
Vol 141 ◽  
pp. 109-122 ◽  
Author(s):  
H. M. Atassi
Keyword(s):  
Small Angle ◽  
Potential Flow ◽  
Angle Of Attack ◽  
Nonlinear Dependence ◽  
Mean Flow ◽  
Linear Superposition ◽  
Flow Angle ◽  
Independent Components ◽  
The Mean ◽  
Gust Response

It is shown that for a thin airfoil with small camber and small angle of attack moving in a periodic gust pattern, the unsteady lift caused by the gust can be constructed by linear superposition to the Sears lift of three independent components accounting separately for the effects of airfoil thickness, airfoil camber and non-zero angle of attack to the mean flow. This is true in spite of the nonlinear dependence of the unsteady flow on the mean potential flow of the airfoil. Specific lift formulas are derived and analysed to assess the importance of mean flow angle of attack and airfoil camber on the gust response.

A Time-Domain Fluid-Structure Interaction Analysis of Fan Blades

2008 ◽  
Author(s):  
Seung Ho Cho ◽  
Taehyoun Kim ◽  
Seung Jin Song
Keyword(s):  
Time Domain ◽  
Vortex Lattice ◽  
Interaction Analysis ◽  
Three Dimensional ◽  
Incoming Flow ◽  
Structure Interaction ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Model ◽  
Blade Row ◽  
Fan Blade

This paper presents aerodynamic and aeromechanical analyses for an entire row of fan blades (i.e. tens of blades with a finite aspect ratio) subject to a uniform incoming flow. In this regard, a new unsteady three-dimensional vortex lattice model has been developed for multiple blades in discrete time domain. Using the new model, the characteristics of the unsteady aerodynamic forces on vibrating blades, including their temporal development, are examined. Also, the new aerodynamic model is applied to examine the aeromechanical behavior of fan blades by using a standard eigenvalue analysis. For this analysis, the fan blades have been modeled as three-dimensional plates, and, increasing the number of blades (or solidity) is predicted to destabilize the fan blade row.

scholarly journals Study on the High-Speed and Close of the UVA Cooperative Formation Controller Design

2018 ◽  
Vol 36 (2) ◽  
pp. 345-352
Author(s):  
Jialong Zhang ◽  
Jianguo Yan ◽  
Pu Zhang ◽  
Xiaoqiao Qi ◽  
Maolong Lü
Keyword(s):  
Dynamic Characteristic ◽  
High Speed ◽  
Controller Design ◽  
Design Method ◽  
Formation Flight ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Model ◽  
Thrust Vector ◽  
The Stability ◽  
Rudder Angle

Aiming at the high-speed flight of the UAVs cooperative formation, when a single UAV has occurred, need to exit the formation flight and be close or super close to form of the formation quickly. A fast close cooperative formation controller design method is proposed to make up for low the fighting robustness, and be shortcomings of timeliness poorly and analyze the dynamic characteristic of UAV formation flight. Taking the external factors known into consideration, setting up for the longitude maneuver of nonlinear thrust vector and unsteady aerodynamic model, according to the formation velocity, flat tail rudder angle and thrust vector and pitch angle velocity for corresponding input commend signals for the controller to research the dynamic characteristic of UAV formation flight. Meanwhile, the formation flight distance error is the convergence to a fixed value, and the stability of the cooperative formation flight is good. The simulation of results show that the controller can effectively improve the speed of the close or super close to formation, and maintain the stability of the formation flight, which provides a method of the close or super close formation flight controller design.

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