The method for aerodynamic characteristics calculation of stores, which are separated from the aircraft

Аuthors

Korizhin O. V.

Russian Aircraft Corporation «MiG», 6, Leningradskoe shosse, Moscow, 125171, Russia

e-mail: olegkorizhin@gmail.com

Abstract

The provision of store release safety is one of the issues that arise during the development of aircraft store transportation and separation systems. In general the safe release refers to fulfilling the following requirements during the store flight in the vicinity of the carrier after its release from the launcher:

— elimination of the possibility of collision of the store with the airplane itself, its structural elements or stores, which are installed on the adjacent suspension points;

— retention of the store spatial stability on the initial segment of its flight path in the vicinity of the carrier;

— absence of thermodynamic impact from the exhaust jet of the store engine on the structure of the airplane itself,its propulsion system functioning and other stores.

It is possible to solve the problem of store separation safety at the stage of transportation system design and release method development. The appropriate solution method is based on the analysis of the results of modeling of store spatial movement in the vicinity of the airplane. At that the reliability of aerodynamic characteristics of the isolated store and flow, which is disturbed by the plane, is important for the simulation.

As a rule it is necessary to conduct wind tunnels tests to obtain aerodynamic characteristics. Reliable determination of safe release modes requires conducting a large number of tests at different angles of attack, sideslip angles and Mach numbers. The presence of folding aerodynamic elements of various configurations on the suspended stores increases the amount of required wind tunnel experiments dramatically. Thus, the determination of aerodynamic characteristics of isolated bodies and interference can take a long time. Conducting tests is generally not feasible at the early stages of system design under uncertainties of some design parameters. In this case it is expedient to use computer technologies, namely, computer engineering methods. Such methods provide reliable analytical support through the use of software suites, which are focused on computational analysis of gas and fluid dynamics (CFD).

The software system, which performs CFD analysis and processes the virtual experiment results, was applied to the analysis of an external fuel tank. Such fuel tanks are widely used on various types of aircraft. Virtual simulations were conducted in a wide range of angles of attack, angles of sideslip and Mach numbers. The results were processed by using a multidimensional (multivariate) interpolation function. Such function allows the research team to calculate the values of the aerodynamic coefficients for the entire range of angles of attack, angles of sideslip and Mach numbers. The relevance of the obtained aerodynamic characteristics was confirmed by the comparison with the available data of the wind tunnel tests. The comparison showed good consistency between the calculation by CFD method and full-scale experiment. Slight differences are most likely associated with the following circumstances:

— ascaled-down model of the fuel tank was tested in the wind tunnel,

— presence of a methodological error in the algorithm, which was used for solving the equations,

— presence of methodological error in the algorithm of gas flow simulation,

— the three-dimensional solid model was simplified for the analysis.

The described method allows the designers to determine the aerodynamic characteristics of the stores at early development stages without conducting the wind tunnel experiments.This can reduce the cost of wind tunnel tests and time, which is required for optimization of the store aerodynamic configuration, significantly.

Application of the proposed multidimensional (multivariate) interpolation allows the designers to calculate the coefficient values for any angles of attack, angles of sideslip, Mach numbers, geometrical configurations and other initial data within a pre-defined range.

The application of the described method allows the researchers to calculate the aerodynamic characteristics of both newly designed and existing aircraft in a wider range.

All of the mentioned above confirms the efficiency of computer engineering methods, especially at the early stages of aircraft design

Keywords:

aerodynamic characteristics, separationsafety, solid modeling system, CFD, CAD, CAE, systemof gas and fluid dynamics analysis, multidimensional interpolation.

References

1. WhatePaper. MentorGraphics^®. How to choose an effective grid system for CFD meshing, available at: http://www.mentor.com/products/mechanical/ resource-center/(accessed 08.02.2014).
2. MATLAB HELP. MathWorks^®. Gridded Interpolant class, available at: http://www.mathworks.com/help/matlab/ ref/griddedinterpolant-class.html(accessed 08.02.2014)
3. Atmosfera standartnaya. Parametry. GOST 4401-81 (Standard atmosphere. Parameters. All-Union State Standard 4401-81),Moscow, Standarty, 2004, 180p.