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Civil Aircraft Testing Technique

#1978


Development of a Complex Technique for Testing Highly-Economical Civil Aircraft in Transonic Wind Tunnels with Slotted Walls

Tech Area / Field

  • SAT-AER/Aeronautics/Space, Aircraft and Surface Transportation

Status
8 Project completed

Registration date
28.08.2000

Completion date
28.09.2004

Senior Project Manager
Kulikov G G

Leading Institute
Central Aerodynamic Institute, Russia, Moscow reg., Zhukovsky

Collaborators

  • European Transonic Windtunnel, Germany, Köln

Project summary

This Proposal is direct continuation of Study performed in the frame of ISTC #592 Project devoted to the wind tunnels with perforated walls. It expands the scope of implementation for developed approach to new branch of transonic wind tunnels. It is proposed to develop the method for correction of the experimental data obtained in the process of testing civil aircraft in transonic wind tunnels with slotted walls. The method is based on the computer code that permits to calculate real configuration aircraft model with boundary condition taking into account. The boundary condition for simulation of slotted walls will be formulated with the use of experimental data. The set of experimental studies will provide the direct simulation of near-slot walls and will give the information for sharp-oriented boundary condition formulation. The technology above will be tested with the use of data obtained in the main European and TsAGI T-128 wind tunnels. This job will be closely connected with requirements of ETW in Cologne and T-128 in TsAGI.

The purpose of the present study is to generalise the previous experience and to develop on this basement the universal technique of experimental data correction. The special features of this study are concerning with the circumstances of tests in European Transonic Wind tunnel (ETW) and T-128 TsAGI. It's supposed to generalise the team knowledge and create the CFD code that takes into account slots’ boundary conditions directly in accordance with ETW and T-128 geometrical parameters. The special experimental studies and reviews of literature are the ways that are to be used for the slot’s boundary condition formulation. The main direction of investigation is to find and to imply the “smooth” boundary condition for CFD code that permits to take into account slots without direct fitting them by means of special grid creation. The additional code that realises special grid (directly fitting the slots) will be created as additional one for the “smooth” code verification.

The base idea of “smooth” code is the same to one formulated in ISTC #592 project for perforated walls. Euler based code needs in boundary condition for inviscid core of wind-tunnel flow. In the case of “fat boundary layer” and out-flow (from wind tunnel to plenum chamber) the boundary layer outer conditions (inviscid core) are quite smooth and contain integral information about slots’ influence. The subject of experimental study is to find empirical formulas to approximate these conditions for CFD implementation. The base parameters for study are:

– distance between slots;


– thickness of boundary layer;
– sizes of slots;
– mass flow through the slots (integral and local);
– vector of velocity direction (integral and local near slots);
– correlation between velocity (or velocity gradients) and static pressure.

The base idea of sharp fitting approach is to create the numerical grid that approximates not only geometry of aircraft and sting but wind tunnel walls with slots of real geometry. This grid is convenient for direct simulation of slot-like boundary condition for Euler equation system. Real boundary layer creates complex flow near the slots. Experimental study is necessary to formulate correlation between velocity vector (or velocity gradients) and static pressure in this case. The purpose of this study is to measure the local parameters of the flow in the vicinity of slots and correct the Euler-type boundary conditions.

It’s clear that “sharp fitting” is usable for “slim” boundary layer but “smooth” – for the “fat” one and final decision about possibility of implementation for these approaches is to be result of experimental and theoretical study.

Theoretical investigation of the subsonic linear problem above with non-linear boundary conditions is the third branch of proposed study. The boundary condition in this case may be formulated with the use of the classical solution for boundary layer and asymptotic solution at super-high Re numbers. The result of this study may be used for verification of CFD code.

Verification of CFD code is the four-step procedure. Step 1: solutions for different grids must be the same; step 2: solution for the same task using different codes must be the same; step 3: CFD solution must predict theoretical case (asymptotic solution of the third branch); step 4: CFD solution must correlate with experimental data. Verification gives two results:

– it shows the quality of code (no-mistake test);


– it shows the quality of theoretical model (experimental formulation of boundary conditions).

CFD data are to be used to estimate blockage and upwash effects because of model presence in wind tunnel. Experimental data will be corrected with the use of these parameters and they will be recalculated on “free stream conditions”.

The main ideas above may be formulated as:

– developing the two CFD codes for “smooth” and “sharp fitting” boundary conditions with taking into account ETW and T-128 geometrical configuration;


– experimental study of integral and local boundary conditions for CFD modelling the flow near the slotted walls;
– theoretical study of linear problem with non-linear boundary conditions;
– use CFD for correction of the experimental data (wind tunnel testing the aircraft models).

The Project purposes correspond to objectives of the ISTC to provide a long-term perspective for civilian professional activity of scientists and engineers involved in this Project. The technologies for taking into account the transonic wind tunnel slotted walls’ influence on results of aerodynamic model tests are widely used for civilian purposes. It's known that the decrease of aircraft drag coefficient by 1% leads to the equal increase of flight distance. In the conditions of growing requirements to ecological safety and fuel efficiency of civil aircraft new generation, this Project proposal provides the long-term perspective of participants involving in civil production and helps to arrange the co-operation between the participants and ETW.

In the course of the work, it is expected to obtain the following results:

– development of universal software (mathematical model of wind tunnel);


– studying the structure of near-slots flow;
– verification of technology above.


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