Influence of surface electrical discharge on friction of plate in subsonic and transonic airflow
| Autor: | Sergey Leonov, Valentin Bityurin, Nicolay Savischenko, Anatoly Yuriev, Valery Gromov |
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| Zdroj: | Scopus-Elsevier ResearcherID |
| Popis: | The paper analyses and discusses results of experimental work on influence of energy release from special organized electrical discharge on characteristics of airflow near plane plate and profiled plate. The experiment was conducted in transonic wind tunnel with closed test section at Mach number M=0.6-1.0. In dependence with Mach number a Reynolds number (on length 1m) was in range l-1.5x!0. Quasi-continuous multi-electrode surface discharge was used for a plasma excitation. Electric energy input to the plasma volume was up to 15kW at area of plate surface 0.012m. Static pressure in a test section was 400-=-700Torr. Different schemes of plasma excitation in respective to test plate position was used. During the test a balance measurements of friction drag and optical observations were fulfilled. Balances measurements give, as a rule, the decrease a tangential force on the plate. Shadow photos show change of a structure of flow near the model. CFD simulation on base of Navier-Stocks equations gives a similar result and allows recognizing the details of interaction. Introduction. At the present time there are a number of theoretical and experimental works, which show that energy release to airflow near/fore streamlined bodies can reduce a total drag of these bodies. In a case of blunted body the drag reduction can be provided with a rather high electiveness even higher than 100% [1-5]. In general case a drag force at zero lift is represented as a sum of three components: shape (pressure/wave) drag, friction drag and a base drag. At the most cases the attention was fixed on pressure and wave share of a total drag. At the same time the drag, which could be associated with a friction, can have a significant part. For modern long-distance airplanes at Mach numbers M = 0.7-0.9 the friction drag value can be estimated in 60% of the total drag value approximately. Herewith only few papers are devoted to the friction problem solution with newly proposed plasma technology [6,7]. There are a couple of papers discussing the pure plasma effects on the surface and near surface phenomena [8]. It should be noted, however, that a so-called MHD boundary layer control when both electrical and magnetic fields are used to modify flowfield and, consequently, to control the surface friction and turbulence development in boundary layers is known for a long time already. Traditional methods of viscous friction reduction are based on a directed mechanical influence on airflow near body surface, actually, it is a control of laminar and turbulent boundary layer. Such a control can be realized by means of two ways: change of velocity vector of an external airflow or/and properties and temperature of the surface. The plasma technique can be useful in two ways by changing of thermo-physical properties of the working media (density, the first and the second viscosity coefficients) and by the flow field modification through the controllable energy release. From the other hand the modification of the friction can result implicitly in a total drag reduction through the boundary layer separation and the laminar-to-turbulence transition phenomena. Thus, the general problem becomes rather complicated and non-linear. Plasma influence on a near surface layers can lead to the contradictory effects. Each aerodynamic situation requires a specific approach to be effected by plasma positively. The experimental observations give important information on details of the interaction. It is expected that the energy addition into the up-coming flow provided by an electrical discharge could result in: (1) stabilization of the boundary layer because of increasing of the heat transfer rate to the 'cold' wall from the 'heated-up' airflow; (2) decreasing of separated flow zones effects on the flow parameters distribution along the body surface; (3) suppressing the laminar-to-turbulent transition by the increasing of the specific energy of the air flow. The results of a model experiment and the preliminary analytical data are discussed in the following sections. (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. Plasma Influence on Friction... 2 AIAA 2001 -0640 T Experimental arrangement and parameters of the test. Experimental installation consists of the following parts: transonic wind tunnel ST-1 with a control panel; aerodynamic model with a build-in balance; plasma generator and power supply; visualization system; data acquisition system, measuring devices and synchronization system. Transonic wind tunnel ST-1 concerns to the type of ejector open-ended short-term operation tubes. The forechamber communicates with the atmosphere and provides an air supply to the nozzle. The highest outlet velocity value can reach the sound velocity value. The further velocity increase takes place due to flow extension. The test section is closed and has a rectangular cross-section of 300x250 mm. For the optical (direct and Schlieren) observation and model monitoring there are several windows closed by protective glasses in lateral walls of the test section. The flow Mach number regulation is made with the help of the shutters set in tunnel walls behind the test section. The ST-1 tunnel allows obtaining the airflow with Mach number that can vary continuously from 0.4 up to 1.17 for a small model. Model. For the research of the friction reduction on a surface with the help of the surface plasma a special model has been designed. The scheme of the model is presented in the Fig. 1. Fig.L Principal scheme of the model. It consists of the following basic components: aerodynamic body (1), installed from one window up to second r— one; immovable small plate from BN (boron nitride) with 17 electrodes (2); movable (large) plate without electrodes (3); holder with the strut (4); strain gauge balance (5); tenso resistive strain gauge bridge elements (6). The body consists of two parts. The base part represents a metal duct with housing for the balance. The top part represents a dielectric wedged nose plate 1,5cm width with a slot for the installation of large and small plates with electrodes. Its upper plane is aligned to the uprunning flow direction. It is attached to the dual-component strain balance that is inside the body. The balance is intended for the large plate aerodynamic drag measurement. Large and small plates (2 and 3) are right-angled. The feeding wires from the electrodes are removed in a base part of the model body. The small plate with electrodes is fixed at the body by the thermosetting adhesive. Electrodes have been made from a cooper alloy. The wires have a good double Teflon insulation. A quasi-continuous multi-electrode surface discharge is used for a plasma excitation at the experiments. Electric energy input to the plasma volume 2-15kW at area of plate's surface 10cm2. An original power supply with individual excitation of each electrode has been used. The PC provides DC power with voltage 5kV from large electrical capacity and high current pulses with a frequency from lOHz up to 5kHz. These pulses go on high voltage transformers, individually for each electrode. Thus all electrodes have an independent excitation of the electric discharge. Ballast resistors manage two functions: limit a discharge current and redistribute the discharge current on all electrodes more-less homogeneously. (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. Plasma Influence on Friction... 3 AIAA 2001-0640 |
| Databáze: | OpenAIRE |
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