tailieunhanh - Influences of the compressibility on aerodynamic characteristics of profile under the transonic flow theory

Numerical results show that the local compressibility depends on not only the speed but also the incidence. At arather great angle of attack, local supersonic regions can appear with free Mach numbers in the order of - the Mach number is normally considered as a speed of incompressible flows. | Vietnam Journal of Mechan ics, VAST, Vol. 29 , No. 4 (2007) , pp . 497 - 506 INFLUENCES OF THE COMPRESSIBILITY ON AERODYNAMIC CHARACTERISTICS OF PROFILE UNDER THE TRANSONIC FLOW THEORY HOA NG THI BIC I-I NGOC Hanoi Universit y of Technology Abstract. Transonic flows are complex problems. At cer tain Mach nu mbers, in gas flows t here are local transitions from the subsonic into the superson ic and reciprocally, especially the discontinuity throughout shock waves. Subsonic flows and supersonic flows have very differen t properties, thus calcu lat ion methods are also different - t he subsoni c equation is elliptic and the sup ersonic equation is hyperbolic. Using established programs (based on the incompressibl e theo ry, the compressible theory and the transonic theory), we studi ed sub-t ransonic flow characteristics with variations of the Mach number. Our studies are a lso carried out with variations of incidence, whi ch impact on t he transon ic effect . Numerical results show that the local compressibility depends on not only the speed but also the incidence. At a rather great angle of attack , local supersonic regions can appear with free Mach num bers in the order of - t he Mach number is nor mal ly considered as a speed of incompressible flows. According to these results, we can recognize for wh ich regime the local compressibili ty of flow is considerable and then it is necessary to consider the problem under t he transonic flow t heory. 1. INTROD UCTION The transonic flow is a mixed flow in which there are locally subsonic and supersonic regions, normally wit h free stream Mach numbers from to (Fig. 1). However , experiences and calculations show that transoni c flow properties depend also on the body geomet ry. By using established programs to calculate flows around a profile, it depend on incidences, a supersonic point can occur even Mach number NI ::; . The transonic flow is a complex problem, especially when taking into account t he

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• Local supersonic regions
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