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Turbulence Influence on Shear, Separated and Swirling Flows

#3013


Study of Wind-Tunnel Turbulence Influence on the Structure and Characteristics of Shear, Separated and Swirling Flows

Tech Area / Field

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

Status
3 Approved without Funding

Registration date
01.03.2004

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

Project summary

Purpose: The purposes of the project are: study of generation and subsequent evolution of flow turbulence in wing tunnels; development of effective methods of turbulence level reduction in test section; development of methods accounting wind-tunnel-turbulence influence on the results of experiment.

Free-stream turbulence has a pronounced effect not only on laminar-turbulent transition in a boundary layer and on the friction drag, but it also changes the configuration of separation zones and, hence, the lift coefficient. Outer flow turbulence of large level leads to increase in heat and mass transfer in turbulent boundary layer. Wind tunnel tests of sphere and flat plate made with different facilities in NACA and TsAGI gave different values of drag coefficient depending on turbulence level. Technique of account for turbulence level influence on drag coefficient developed in course of preliminary studies eliminates this discrepancy. However, this technique is not suitable for bodies of arbitrary shape and for account for influence of turbulence level on lift coefficient. For radical improvement of it, the deep insight into the nature of turbulence and it’s evolution in basic types of flow are necessary. Experimental and theoretical investigations of influence of wind-tunnel turbulence on shear, swirling and separated flows proposed in the project will provide this knowledge. Two general lines of investigations are proposed:

- Study of generation and breaking of turbulence by grids, screens and honeycombs and it’s subsequent evolution in confuser flow. Development of effective methods of turbulent flow production with prescribed characteristics (turbulence level, isotropy, and scale).

- Investigation of influence of free-stream turbulence on the structure and parameters of shear, swirling and separated flows. Development of physically substantiated method accounting turbulence level influence on results of wind tunnel experiment.

Expected Results and their Application

The following general results will be obtained:

- New method of turbulence level reduction in test section of wind tunnel.

- Technique of generation of high-intensity turbulence (e ~ 10-20%) with minimal energy consumption.

- Original method of transition location prediction in the boundary layer on the blunt bodies in flow with moderate turbulence level.

- Models of swirling and separated flows with different levels of free-stream turbulence. Methods of account for turbulence intensity influence on characteristics of these flows.

- Model of free stream turbulence influence on characteristics of turbulent boundary layer accounting the combined effect of Reynolds number, turbulence intensity and scale.

- New method of account for turbulence intensity influence on lift and drag coefficients of bodies of arbitrary shape.

Results obtained may be used for reduction of turbulence level in existing and new wing tunnels. They also will assist in improvement of accuracy of wing-tunnel test results extrapolation to flight conditions. Results of study of heat transfer intensification by means of flow turbulization may be used in various technological equipment.

Technical approach and methodology

Project includes predominately experimental investigations which will be performed in low-turbulence wind tunnels of TsAGI. Free-stream turbulence of intensity (e ~ 1-20%) in the test section will be generated by grids or perforated plates. Average values and pulsations of streamwise and normal velocities will be measured by pitot tubes and hot-wire anemometers. Pulsation’s spectra and auto- and cross-correlations will be found by means of digital signal processing. This makes us possible to find the streamwise and transverse lengthscales of turbulence and estimate the degree of its isotropy. Skin friction and heat transfer in the turbulent boundary layer will be determined from the velocity and temperature profiles in the viscous sublayer. Specially developed in TsAGI technique accounting for influence of velocity gradient and wall-effect will be applied for measurements of velocity profile. Project also involves theoretical investigation of free-stream turbulence influence on structure and characteristics of shear, curled and separated flows. It includes the study of boundary layer receptivity to oncoming vortical perturbations and subsequent linear and nonlinear development of resulting disturbances in boundary layer. Computations of curled and separated flows will be conducted in the framework of full Navier-Stokes equations with various one- and two- parametric models of turbulence. During these computations the experience of similar problems solution acquired in course of work under project ITSC#199-95 will be used.

Scientific and Commercial value

The project refines the understanding of physical mechanisms of turbulence development in shear, separated and swirling flows and the influence of free-stream turbulence on the aerodynamic characteristics of different shape bodies. Effective methods of turbulence reduction and generation of turbulent flows with predetermined parameters elaborated will improve the characteristics of wind tunnels and technological equipment. The results obtained will also improve the accuracy of wind-tunnel tests results extrapolation to flight conditions.

Meeting ISTC Goals and Objectives

This project fully comply to the aims of ISTC, because:

- The project is directed at the solution of urgent scientific and technical tasks which are important for the civil aviation. Results will be obtained also may be useful for improvement of efficiency of technological equipment such as reactors, fermenters and heat exchangers.

- The result of this project possess of commercial potential and hence, without doubt, contributes to the conversion to the market economy.

- The project utilizes directly the fundamental scientific potential and the experience of investigator groups from TsAGI, previously engaged in aircraft military programs.

Role of Foreign Collaborators

Our potential partners are specialists in the area of aerodynamic experiment, theory of turbulence and aircraft aerodynamics.

The following non-financial participation of collaborators:


- informational exchange in the course of the project;
- cross-examinations of the results obtained during the project;
- assistance in commercial applications of elaborated techniques of turbulence reduction and generation of high-turbulent flows;
- joint symposiums and seminars.


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