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Civil Aircraft Testing

#3085


Investigation of Steady and Unsteady Phenomena in Transonic Wind Tunnels with Slotted Walls to Improve a Complex Technique for Testing Highly-Economical Civil Aircrafts

Tech Area / Field

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

Status
8 Project completed

Registration date
21.07.2004

Completion date
31.01.2008

Senior Project Manager
Ryzhova T B

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

Collaborators

  • European Transonic Windtunnel, Germany, Köln\nAérospatiale Airbus, France, Toulouse

Project summary

This Proposal is direct continuation of Study performed in the framework of ISTC #1978 Project. During the final workshop on the #1978 Project it was concluded that CFD model of ETW (European Transonic Wind tunnel) on the basis of Euler equations could be used for correction of experimental data. In this Proposal, a new approach to simulation of flows in ETW and T-128 (working part #3) is proposed. This new approach will allow to investigate stationary and non-stationary phenomena in these wind tunnels with taking into account the effects of viscosity and turbulence. For this purpose, it is necessary to continue the development of CFD code on the basis of RANS (Reynolds-averaged Navier-Stokes equations). Preliminary version of this code was presented as additional part of ISTC #1978 Project. Verification of this code using experimental data confirmed the reliability of implemented method. It is also proposed to enhance the method for correction of experimental data obtained in the process of testing civil aircraft in transonic wind tunnels with slotted walls. The method developed in the #1978 Project is based on linear computer code that permits to correct the experimental performances of the model to take into account the influence of wind tunnel walls. It uses “distributed” boundary conditions. These boundary conditions were formulated on the basis of experimental data. It is proposed to increase the range of linear technology implementation up to transonic Mach numbers (M~0.85). This job will be closely connected with requirements of ETW in Cologne and T-128 in TsAGI.

The purpose of the present Project is to generalize the previous experience and to develop on this basement a universal technique of experimental data correction for wind tunnels with slotted walls. It's supposed to generalize the team knowledge and to create RANS CFD code that calculates flow in accordance with ETW and T-128 geometrical parameters. To achieve this goal, it’s supposed to perform the special experimental studies to define more exactly the mathematical formulation of task. Review of literature will allow to choose the most appropriate method for investigation. The code will be verified using ETW experimental data. Special experimental investigation in T-125 wind tunnel (TsAGI) is also supposed.

The subject of experiments is to investigate fine features of non-stationary slot’s flow. Task formulation is simplified due to the fact that the experimental model is already exists: it was designed and manufactured in the framework of #1978 Project. It is proposed to modify this model by installing additional tools for investigation of unsteady phenomena in the slots. It is also supposed to modify the model for additional for optical investigations. Measurements of non-stationary flow parameters will be performed using small-size fluctuation gauges and thermoanemometers.

The main component of the proposed numerical methodology is a special algorithm of computational grid generation with fitting the geometry features (both features of the wind tunnel and features of the aircraft model). Below this is called “sharp-fitting” approach. It is supposed that in calculation all main elements of geometry will be taken into account: test section of the wind tunnel, plenum chamber, slots in the walls, re-entry flap, sting, model, etc. Computational grid will be compressed to the surfaces of all investigated bodies to allow the computation of near-wall viscid flow (boundary layer). As a basic numerical approach, the point-implicit monotone numerical method of 2nd approximation order will be used. To accelerate computation, the method of fractional timesteps will be developed. This method will ensure the correct description of non-stationary processes. In the framework of this approach, one global timestep (equal for all computational cells) is pided into many local timesteps (with different quantity of local timesteps in different cells). Quantity of local timesteps in concrete cell depends upon local stability condition. This method may be realized using multiprocessor computers. It is proposed to manufacture cluster from Pentium computers and to develop new code on the base of MPI technology.

Verification of CFD code will be organized using four-step procedure. At the Step 1, a comparison of solutions for different grids is performed. At the Step 2, an idea that solution of the same task using different codes must be the same is verified. At the Step 3, the numerical solution convergence to theoretical solution (e.g. asymptotic solution) is investigated. At the Step 4, the correlation of CFD solution with experimental data is verified. Verification will answer on two types of questions: 1) are there mistakes in the code; 2) do the mathematical models (for example, turbulence model) correspond to the requirements for simulation of the investigated flows.

Presence of the aircraft model in the wind tunnel results in the following main effects: 1) variation of Mach number in the reference point of the wind tunnel and in the vicinity of the model (blockage); 2) variation of the effective angle of attack (additional upwash). CFD data will be used to estimate these effects. Experimental data will be corrected with the use of these estimations and will be recalculated on “free stream conditions”. Non-stationary effects, which arise around slotted walls, will be investigated too.

The main ideas of this work may be formulated as follows:

· Developing RANS CFD code with taking into account the geometry of ETW and T-128 wind tunnels.


· Experimental study of non-stationary flow characteristics near the slotted walls.
· Determination of the linear method applicability limits at high subsonic velocities using comparison with CFD data obtained with RANS code.
· Using CFD code for correction the experimental data (free stream conditions).

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 new generation civil aircraft, 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:

· the methodology will be developed for computation of stationary and non-stationary flows in wind tunnel on the basis of averaged Navier-Stokes equations, closed by various turbulence models;


· the non-stationary flow structure near the slots will be developed, and methods for diminishing the fluctuations of flow parameters will be proposed;
· verification of the above technology will be performed.


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