On the Boundary Value Problem With Experimentally Determined

                            Boundary Conditions



It is well known that even the best wind tunnels do not provide the flow over

a model that would exactly simulate the free air stream condition i.e. to be

the same as the flow in free air. Hence, the problem of wind tunnel wall

interference accompanies experimental and theoretical investigations when

designing a wind tunnel as well as during its operation.



The influence of perforated walls of transonic wind tunnels at two-dimensional

investigations by employing the Fourier's method for solving Dirichlet's problem

formulated for a rectangle of wind tunnel's work section is given in this

paper.



In order to preserve the realistic features of flow at the work section's

boundaries the boundary conditions, which are to be known to solve this type of

boundary problem, are experimentally determined by measuring static pressure

distribution at the vicinity of work section walls.  To solve the formulated

problem, the concept of local linearization of external flow far from model and

flow over it has been used.  This flow has been replaced with singularities of

appropriate strengths.



In the paper the boundary value problem has been analyzed by adapting the

solution for application of Fourier's transformation. Fourier coefficients

have been computed with fast Fourier's transformation. The method for solving

this type of problem is given, along wit
ution and its convergency.



To demonstrate the appropriateness of the presented algorithm for calculation

of transonic wind tunnel wall interference at two-dimensional investigations,

the algorithm has been applied to the aerodynamic experimental results from

investigations of NACA 0012 airfoil obtained in VTI-Institute Zarkovo

(Yugoslavia).



    Associate Professor, Dr.-Ing. Bosko Rasuo,

    Aeronautical Department,

    Faculty of Mechanical Engineering,

    University of Belgrade,

    27 Mart 80, 11000 Belgrade,

    Yugoslavia.

    Fax: 381 11 3370 364,

    Email: erasuo@ubbg.etf.bg.ac.yu