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2015 | OriginalPaper | Buchkapitel

3. Unsteady Aerodynamic Modeling

verfasst von : Ashish Tewari

Erschienen in: Aeroservoelasticity

Verlag: Springer New York

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Abstract

This chapter details the various methods of deriving an unsteady aerodynamic model for aeroservoelastic analysis. This usually takes the form of a linear operational relationship between pressure distribution and upwash distribution on a lifting surface for subsonic and supersonic flows, and a nonlinear partial differential equation (Euler, full-potential, or transonic small-disturbance equation) for transonic flows. The treatment of the flow models for inviscid as well as viscous flows, and for various speed regimes is presented. Detailed derivations include the incompressible vortex-lattice methods, analytical models, Green’s integral formulations, velocity potential and acceleration potential integral equations for compressible subsonic and supersonic flows, and transonic small-disturbance models. Numerical schemes are described in detail for subsonic Doublet-Lattice, supersonic Mach-Box, supersonic Doublet-Point, and transonic Doublet-Lattice methods.

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Fußnoten
1
It can be verified that Eq. (3.30) is alternatively expressed as follows:
$$\begin{aligned} \Phi_{\xi\xi}+\Phi_{\eta\eta}+\Phi_{\zeta\zeta}=\frac{1}{a^2}\Phi_{tt},\end{aligned}$$
where the fluid-fixed coordinates \((\xi,\eta,\zeta)\) are obtained from the body-fixed coordinates \((x,y,z)\) by the following Galilean cum Lorentz transformation :
$$\begin{aligned} \left\{\begin{array}{c} \xi\\ \eta\\ \zeta\end{array}\right\}=\left\{\begin{array}{c} x\\ y\\ z\end{array}\right\}-\textbf{U}t.\end{aligned}$$
 
2
Green’s integral formulation for unsteady, potential, compressible flow is discussed later in this chapter.
 
3
Wagner function \(k_1(s)\) models the indicial lift of a flat plate airfoil impulsively started from rest by
$$\begin{aligned} L(t)/L(\infty)=k_1(s)+\frac{b}{2}\delta(s),\end{aligned}$$
where \(s=tU_{\infty}/b\) and \(\delta(s)\) is the Dirac delta function.
 
4
Unfortunately, there is a mistake in Eq. (13.134) of Katz and Plotkin [86], which has been corrected here.
 
5
Not associated with the circulation due to wake.
 
6
Note the upper limit of the streamwise integral is \(x_m=x\) in the limit \(z\to 0\).
 
7
The strength \(4\pi\) of the doublet for defining the kernel is the convention adopted by the workers in this area, and relates to a sphere of unit radius centered at the doublet as the elemental control volume in Green’s integral.
 
8
Such a choice of line doublet and control point is borrowed from the vortex-lattice method  [86], where a quarter-chord line-vortex and a three-quarter chord control point for enforcing the upwash boundary condition automatically satisfy the Kutta condition for steady incompressible flow past a flat plate.
 
9
The spatial integration over the sphere yields the following:
$$\begin{aligned} -\int\!\!\!\int_{S_{\epsilon}} {\left(f\frac{\partial \Phi}{\partial n}-\Phi\frac{\partial f}{\partial n}\right) \textrm{d}S_{\epsilon}}=\left(\epsilon\frac{\partial \Phi}{\partial n}-\Phi\right)\delta(t-\tau+\epsilon/a_{\infty})\end{aligned}$$
 
Metadaten
Titel
Unsteady Aerodynamic Modeling
verfasst von
Ashish Tewari
Copyright-Jahr
2015
Verlag
Springer New York
DOI
https://doi.org/10.1007/978-1-4939-2368-7_3

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