Volume 17, Issue 1 (2017)                   Modares Mechanical Engineering 2017, 17(1): 353-364 | Back to browse issues page

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Nejati M, Shokrollahi S, Shams S. A Comprehensive Model to Compute Incompressible-Subsonic Compressible Unsteady Aerodynamic Loads using Indicial Functions. Modares Mechanical Engineering. 2017; 17 (1) :353-364
URL: http://journals.modares.ac.ir/article-15-8301-en.html
1- Faculty member- Malek Ashtar University
Abstract:   (1632 Views)
In this paper, a novel model based on the indicial functions concept is presented to calculate the unsteady aerodynamic loads in the incompressible and subsonic compressible flow. Indicial functions represent the two-dimensional airfoil response to a unit step change in the angle of attack or the pitch rate about the reference axis. In contrast to the incompressible flow where the aerodynamic loads can be determined in terms of a single indicial function, four indicial aerodynamic functions are required to find them in the compressible one. If the indicial functions are known, the unsteady loads can then be obtained through the superposition of indicial responses using Duhamel’s integral for any arbitrary motion. For the purpose of combination the aerodynamic loads for the entire subsonic flow speed range, i.e. 0≤M≤0.8, a new, efficient and Mach dependent approximations of the indicial functions are presented by using the analytical as well as numerical data. Using four instead of seven Mach dependent coefficients in the common indicial functions, the required coefficient are decreased from 28 to 16 to fully describe the aerodynamic loads. Utilizing the indicial functions, then a novel and convenient form of unsteady aerodynamic loads and the corresponding state-space representation is presented; having a unified formulation in incompressible and subsonic compressible flight speed regimes. Based on the strip theory as well as the modified lift curve slope, the finite span effect of 3D wings is also included. The generated indicial functions is validated against available results, which shows a good agreement.
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Article Type: Research Article | Subject: Aerodynamics
Received: 2016/10/9 | Accepted: 2016/12/30 | Published: 2017/01/17

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