Flow Control for Modern Passenger Aircraft
Investigation and Development of New Methods of Flow Control for Modern Passenger Aircraft Aerodynamics Improvement
Tech Area / Field
- SAT-AER/Aeronautics/Space, Aircraft and Surface Transportation
8 Project completed
Senior Project Manager
Ryzhova T B
Central Aerodynamic Institute, Russia, Moscow reg., Zhukovsky
- AIRBUS Industrie, France, Blagnac
Project summaryPurpose: The further progress of modern aircraft to a considerable extent depends on the new methods of flow control development. In this connection it is necessary to know the flow receptivity to different governing natural and artificial influences. Various flow control methods are developed and used now (geometry optimization, boundary layer suction, blowing/jets and so on). But further progress of commercial efficiency, safety and ecology of aviation demands new flow control methods development. The aim of the present project is to study theoretically several new flow control methods and to estimate their aerodynamic efficiency. The control method is the most effective if it is applied to the most receptive processes. The main part of the project is concerned with control of laminar-turbulent transition in boundary layer which is one of the very sensitive processes. The new possibilities to control turbulent boundary layer, boundary layer-shock wave interaction on transonic airfoil will be considered too. To develop the new control methods it is intended to refine physical and mathematical models of some flows, to develop corresponding computational methods, and to carry out appropriate parametric research.
This project is the development of investigations under the framework of the ISTC project #199-95 on civil aircraft drag reduction enabling decrease of fuel consumption . The new project provides more thorough investigations, which are very important both for economy and ecology. There will be investigated a number of new methods of drag reduction and other flow control methods, which increase flight safety as well.
Boundary layer receptivity to free-stream vortical disturbances (natural and wind tunnel) for straight and swept wing. Receptivity control.
Investigations proposed include the study of steady vorticity normal to leading edge interaction with boundary layer over straight and swept wing. The flow outside the boundary layer will be found using rapid distortion theory. Development of resulting disturbances in the boundary layer will be found by PSE-method. The cross-flow instability modes generation due steady flow non-uniformity/swept wing interaction will be studied too. The knowledge of receptivity mechanisms obtained will be applied to elaboration of transition delay methods.
Control of cross-flow dominated transition.
Cross-flow instability is one of important cause of laminar-turbulent transition in the boundary layer at swept wings of modern transport aircrafts. The most investigated technique of such transition delay is boundary layer suction. But many problems still exist for practical use. Because of this, the elaboration of new alternative methods of cross-flow dominated transition delay is an urgent task. This part of the project is devoted to theoretical design of such alternative technique based on artificial disturbances introduction into boundary layer. In natural conditions laminar-turbulent transition is triggered by steady cross-flow instability mode. This mode will be referred as basic mode. The investigation proposed is aimed to demonstrate the basic mode growth suppression by means of generation of another cross-flow instability modes. These artificial disturbances should change the basic flow properties in such a way as to prevent the growth of basic mode. Artificial disturbances itself should be chosen so that their growth saturates and do not lead to transition. It is proposed to study both steady and non-steady artificial disturbances (MEMS). The parameters of artificial disturbances (amplitude, frequency and spanwise period) giving the best basic mode growth suppression will be chosen in course of theoretical studies of different cross-flow instability modes interaction. DNS and non-linear PSE codes will be used in these studies. The efficiency of the suggested methods of transition delay by the artificial disturbances will be assessed.
Semi-active control of laminar-turbulent transition in 3D compressible boundary layer.
This item will be devoted to theoretical investigation of laminarization of boundary layer on swept wing using steady artificial irregularity (semi-active control). Laminar-turbulent transition is assumed to be caused by free-stream disturbances (sound or flow vorticity) or roughness of the wing surface. The general idea of the laminarization method proposed is in mutual cancellation of unstable modes excited by external disturbances in the vicinity of leading edge of wing and over artificial irregularity of wing surface. This cancellation becomes possible because of the special choice of the irregularity location and amplitude (in order to achieve phase opposition between the incoming and artificial instabilities). As these two modes are exited by the same external disturbance, the tuning of irregularity parameters doesn’t depend on amplitude and phase of this disturbance. Thus, the physical mechanisms of the method consist in total receptivity relaxation.
Various types of artificial (MEMS) irregularities will be considered. The optimum type and the longitudinal form of the irregularity will be found in order to prevent generation of ‘by-pass’ transition immediately over controlling MEMS irregularity.
Investigation of thermal transpiration phenomenon.
Thermal transpiration phenomenon will be studied in this item using theoretical and numerical methods.
Thermal transpiration method is based on thermal slip effect: there is slip velocity along the surface if tangential gradient on it exists. If a surface is inner surface of pore in porous membrane then the gas flow arises if the temperature difference between both sides of porous membrane is imposed. The important feature of this flow control method is the high uniformity of flow rate through membrane, which results from small diameter of pore of membrane. The mathematical model of gas flow in such small channels and porous membrane is based on kinetic theory of gases (Boltzmann equation). Numerical investigation of flow through porous medium with the help of kinetic approach will be carried out by direct simulation Monte-Carlo method (DSMC) and other Monte-Carlo methods. Asymptotic limiting flow regime in porous medium and flow in connecting channels will be investigated by the Navier-Stokes equations.
The numerical and analytic results will permit to determine optimal values of flow rate, geometric, temperature and other parameters of thermomolecular (Knudsen) pump and to estimate the energetic efficiency of thermal transpiration boundary layer control method with conjugated heat and mass transfer processes.
Flow control by electrogasdynamical methods.
Different electrogasdynamic (EGD) methods will be investigated to assess possibility both laminar and turbulent boundary layer flows control. An influence of direct current (DC) plasma actuators on evolution of the Tollmien-Schlichting disturbances in laminar boundary layer on a flat plate will be studied. The boundary value problem modeling an influence of spatially-periodic volume force generated by plasma actuators on cross-flow type disturbances in boundary layer on an infinite span swept wing will be formulated and solved. The efficiency of the EGD methods for laminar-turbulent transition delay will be assessed.
Physical model of plasma actuators based on dielectric barrier discharge (DBD) and operating in air flows as well as appropriate computer codes will be developed. Using these codes an impact of DBD plasma actuators on laminar and turbulent boundary layers will be studied.
A qualitative theoretical estimation of DC plasma actuator influence on turbulent boundary layer will be obtained. A model for turbulent skin friction involving consideration of quasi-streamwise vortices in the cross-stream plane will be developed to study the effect on the skin friction of EGD-interaction generated by DC plasma actuator.
The efficiency of such flows control as EGD-influence by local regions of heat and volume force additions, relaxation processes on shock wave/boundary layer interaction in transonic flows will be studied on the base of solution of time-dependent Reynolds averaged Navier-Stocks equations (URANS-method) with the utilization of the wide used two-equation SST model of turbulence.
Expected Results and their Application.
Several new methods of boundary layer control will be investigated and their efficiency for drag reduction and buffet onset delay will be assessed. The most effective and beneficial methods among considered will be chosen and recommended for subsequent experimental verification and refinement. The positive results will promote passenger aviation fuel consumption reduction and increase of flight safety.
Technical approach and methodology
Development of new control methods are based on laminar boundary layer stability and receptivity and turbulent boundary layer structure investigations. Analytical and computational methods will be utilized.
Scientific and Commercial value
The project refines understanding of physical mechanisms of boundary layer flows control. Several new research approaches and practical recommendations will be developed. It is hoped that results obtained may be used by designers to improve aircraft aerodynamic characteristics, commercial efficiency and safety.
Meeting ISTC Goals and Objectives.
This project fully complies to the aims of ISTC, because:
- The project solves fundamental and applied problems important for commercial civil aviation.
- The results of this project have commercial potential and hence, without doubt, contribute 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, and thus provides high-qualified specialists with an alternative employment and contributes to involve them in international scientific community.
Role of Foreign Collaborators.
Our Collaborators are specialists in aircraft aerodynamics.
The following non-financial participation of supposed collaborators:
- informational exchange in the course of the project;
- cross-examinations of the results obtained during the project;
- testing and evaluation of the technologies developed in the course of the project;
- assistance in commercial applications of results obtained;
- joint workshops and seminars.
1. Final report ISTC-199-95.
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