Eksperimentalna studija o uticaju igle na nadzvučno i okolozvučno opstrujavanje tela polusfernog vrha

Abstract

Snažan udarni talas, koji nastaje pri nadzvučnom letu projektila zaobljenog vrha, značajno povećava njegov otpor i aerodinamičko zagrevanje. Oba efekta mogu da se umanje montiranjem igle na vrh projektila. Osim postojanja same igle, i njena dužina i oblik takođe mogu da utiču na aerodinamičke karakteristike zaobljenog tela. Ovaj rad prikazuje eksperimentalne rezultate uticaja oblika igle na aerodinamičke koeficijente sila i momenata, kao i na poziciju centra pritiska, pri nadzvučnom i okolozvučnom opstrujavanju modela projektila polusfernog vrha. Eksperiment je izveden u trisoničnom aerotunelu pri Mahovim brojevima M =1,89 i M =1,03 i različitim napadnim uglovima (0○ -10○ ). Vizualizacija strujnog polja pri nadzvučnom opstrujavanju modela izvedena je šliren metodom. Ona je omogućila kvalitativnu analizu strujnog polja vazduha oko modela bez igle i modela sa četiri igle različitog oblika. Na osnovu vizualizacije strujnog polja izvedeni su zaključci koji su u skladu sa dobijenim brojnim vrednostima aerodinamičkih koeficijenata. Eksperimenti pokazuju da igla i njen oblik imaju uticaja samo pri nadzvučnom letu projektila, dok igla ne utiče, ili čak malo pogoršava aerodinamičke karakteristike projektila pri okolozvučnom letu. Dobijeni rezultati se mogu šire primeniti, na primer pri projektovanju supersoničnih letilica.

A strong shock wave during a supersonic flight of a blunt-nosed projectile increases the drag and aerodynamic heating considerably. A spike can be mounted on the nose of the projectile to reduce these effects. Apart from its very existence and its length, the spike's shape may also affect the aerodynamic characteristics of a blunt body. This paper presents the results of an experiment that analyzed the influence of the spike's shape on the aerodynamic forces and moments coefficients, and the location of the center of pressure, at supersonic and transonic flows past a model of a projectile with a hemispheric forebody. The experiment was carried out in a trisonic wind tunnel, for Mach numbers M=1.89 and M=1.03 and different angles of attack (0○ -10○ ). Visualization of the experiments was performed by the schlieren method in the case of supersonic flow. It enables qualitative analysis of the airflow around the tested model without and with four different spikes. The conclusions are by the obtained values of the aerodynamic coefficients. The experiments show that a spike and its shape affect only the performance of the tested projectile during its supersonic flight. Besides, a spike does not affect or even slightly impairs the aerodynamic performance of the projectile during its transonic flight. The obtained results are applicable in broader contexts, e.g. for the design of an aircraft for supersonic flights.