Üç boyutlu bir cisim üzerindeki akımda statik basınç ölçümleri

Abstract

Uçaklara takılan harici yapıların, uçağın uçuş verimliliğini mümkün olduğunca az etkilenmesi için, deneysel çalışmaların yapılması ve sonuçların gözden geçirilmesi gerekmektedir. Bu tez çalışmasında eksenel simetrik yapıya sahip bir bomba adaptörü (Temel model) ile bu adaptör geometrisine yeni yapıların eklenmesi ile oluşan çeşitli modeller kullanılmıştır. Statik basınç ölçümleri alkollü bir manometre ile ölçülmüştür. Statik basınç ölçümleri a = -i5°,0o,l5° hücum açılarında, sıkışamaz akış şartlarındaki v = 28. 5 m / s uniform hava hızında yapılmıştır. Tüm deneyler 1 10 x80 cm 2 kesitli 00 deney odasına sahip İ.T.Ü. Gümüşsüyü ses altı rüzgar tünelinde yapılmıştır. Deneyler sonucunda model üzerinde basınç ölçümleri gerçekleştirilmiş akımın ayrılma odak noktaları, yapışma çizgilerinin yerleri saptanmıştır. Akım karakteristiklerinin ölçülmesine sıcak tel anomemetresi ve LISFM (Laser Interferometer Skin Friction Meter) tekniği ile yüzey sürtünmesi ölçümleri yapılarak devam edilecektir.

Most military stores are carried externally. External carriages facilitate the interchangeability of a wide range of stores and is often associated with a lower release disturbance than internal carriages. An aircraft designed for external store carriage can be made smaller and lighter than an aircraft with an internal carriage. However, external carriages make a considerably large, two-fold contribution to the total drag of a loaded aircraft : in addition to a drag of their own, external carriages cause an inteference drag which depends on the installation arrangement. However, designers of modern aircraft must pay painstaking attention to the design of stores and carriages, and also to their compatibility with the aircraft body. Reduction of the interference drag is accomplished through modifications of the flow interactions between the store and the aircraft. On the other hand, minimization of external store drag involves selection of a proper form which eliminates all drag producing features. Slender and axisymmetrical bodies have an importance in aeronautical applications. Missiles, rocket, aircraft fuselages and fuel tanks are some examples of such bodies. The surrounding flow field causes some aerodynamic forces acting on these bodies. For a better performance for such bodies, these aerodynamic forces at different flight speeds, Reynolds number and angles of attack must be examined. This can be done by making aerodynamic investigations and pressure measurements on these bodies. The subject has not been understood completely yet and in order to improve the security and performance there is a strong need for such studies. In aeronautics, the external storage position and the forces which are formed on these parts of the body and their effects on the total aerodynamic force are very important, from the point of view of the aircraft performance. It is well-known that external fuel tanks and rockets increase the drag to some extent. In the mean time, it is necessary to do an extended study about wing and fuselage intersection regions by investigating their effects on the aircraft performance. Even if an external storage causes negative effects, many times it is necessary to use it. It is necessary to do experimantal and numerical study for approximating the dilemma constructively to an optimum point. In the present study, the static pressure measurements have been done firstly on the symmetry axis of the bodies and then performed in three dimensional form. VI By using different nose and tail configurations, it has been understood that a proper geometry can be found. The hot wire and LISFM ( Laser Interferometer Skin Friction Meter ) measurments will be completed in the near future. All the experiments have been performed in the I.T.U Gümüşsüyü subsonic tunnel which has a 80*iicbw2 experiment chamber with a V^ =28.5±0.5m/sn free flow velocity. The free flow turbulence intensty is 2%. Reynolds number with respect to the model length is between ı. 06 x 10 6 £ Re £ 1.337 xlO 6. The Reynolds number corresponding to the maximum model diameter is i.97*io5. The angle of attack has been changed a = -1 5°, 0°, 1 5° In this study, the model without rocket-launchers and a tail has been named basic model ( Model 1A ) Figure 1. With the addition of the rocket-launchers to basic model, model 1C has been formed ( Figure 2. ), and with the addition of the tails which have different geometries to 1 A, model 2B and model 2G have been formed as shown in Figure 3. and Figure 4. The static pressure measurments have been taken on the symmetry axis for all of the model geometries. 116 420 MODEL 1A Figure 1. Model 1A MODEL ÎC Figure 2. Model 1C Vll Three dimensional pressure measurments have been taken only on the model 1 A. The measurements which have been taken on the symmetry axis show that the pressure distributions of the model 1A, 2B, 2G models are approximately the same a 1* " 100 J p = 1A° Figure 3. Model 2B of LsJ ^ =20 Figure 4. Model 2G Geometry of the paraboloidal forebody, in terms of R/R0, can be described by the following fourth order polynomial with an accuracy better than 1%. R. = -0. 0436 774 +0.31 55 7/3-0. 9625 ?72 +1.5079 77+ 0.028 VIll Where R is the radial location of the forebody surface in the symmetry plane, r o(50mm) is the maximum radius of the paraboloid forebody and tj is the normalized axial distance measured from the tip of model. "-% R. An attempt was made to trip the boundary-layer on the forebody by placing wires of 0.5mm. and 1.5mm. in diameter at X=20mm. However, the trip wires did not cause any observable effect on the static pressure distributions on the models. Therefore, it can be hypothesized that the laminar boundary-layer developing on the forebody becomes transitional or turbulent before it reaches the step located at X=116mm. The paraboloidal forebody was instrumented with 24 pressure taps which were placed 5mm. apart in the axial direction. The forebody could be rotated around the model axis so that this single line of pressure taps could be used to measure the static pressure all around the forebody. The backward facing step at the end of the forebody was also instrumented with 74 pressure taps which were located 5mm. apart in a squared grid (surface A). The lower surface (surface B) instrumented with 123 pressure taps which were located 10mm. apart in a square grid. Finally the upper surface (surface C) was instrumented with 145 pressure taps which were located 10mm. apart in a squared grid. The static pressure coefficient Cp for the angles of attack of a = -15o,0°,15o has been measured on the symmetry axis of the models in the condition of three dimensionality by using a manometer with alcohol. Summary of conclusions 1-) Two seperation lines were observed on the lower surface (surface B) at a = -15°. Footprints of a pair of counter-rotating tornado vortices were observed on the step surface (surface A) at a = -15°. 2-) Good agrement was observed between the static pressures measured and calculated on the axis of model 1A. 3-) Experimental static pressure data indicated that afterbodies did not cause any significant changes in the static pressure field of model 1A. Therefore, it was argued that the drag reduction provided by afterbodies was mainly due to the contraction of the reverse flow region at the trailing edge. IX 4-) Contour plots of the static pressure coefficient measured on the forebody of the basic model 1 A showed that constant pressure lines were inclined roughly at angles of ±55 ° near the model tip at a = ±15°. 5-) A contour plot of the static pressure coefficient measured on the step surface (surface A) revealed circular contours which appeared to be related to the tornado vortices.