Research Of Second Throat Design Of Continuous Transonic/Supersonic Wind Tunnel

Owing to the need of the continuous transonic/supersonic wind tunnel which is more and more urgent in our Country, the research of 4.8m continuous transonic/supersonic wind tunnel has already begun. In order to ensure that the 4.8m wind tunnel meets the refine request of the wind tunnel experiments and becomes an advanced transonic wind tunnel in the world, its design index of the flow field gives a higher request. As an important section of the wind tunnel, the design of the second throat is one of key techniques of the research about the transonic wind tunnel.The second throat has already got the extensive application in existing wind tunnel equipments. It can insulate the upstream and downstream flow field resulting in the noise drop of the text section from the downstream and can control the Mach number exactly in the transonic state. When the air passes, the second throat makes use of variational section area to change the speed of the air and coming into being a shock wave of which the Mach number is just greater than 1 in the minimum piece of the second throat. This process induces the choking which becomes the key to control the Mach num exactly in a transonic/supersonic wind tunnel. In the supersonic state, the second throat can improve the efficiency of the wind tunnel notablely. Via reducing the Mach number of the shock wave, the loss of the wind tunnel is reduced and the efficiency of the wind tunnel is improved.In order to design the second throat which meets the requirement in the method of the numerical simulation, some researches on the second throat of the transonic wind tunnel are carried out in this paper. The second throat can be divided into fixed type and adjustable type. Because of the more advantage of the adjustable type, the designing wind tunnel will use this type. The adjustable type can be divided into type of center chock, type of flap, type of choke finger. The different adjustable ways of the throat have decided the different applicability. The type of center choke has an unwieldy configuration and can't be regulated easily, so, this paper makes the important point on the type of flap and choke finger.After validating the numerical method with some standard cases, both the second throat with flap and with choke finger is studied by numerical simulation. Firstly, a group of 2D models are established to study how contraction, straight segment, diffuser influence the performance of second throat. The results indicate that the size of contraction has significant impact on second throat performance. The speed of the air changes the most violently in this section. If the length is shorter, the speed of the air will vary very fast and this section will increase the loss of the throat. The size of the straight segment and the diffuser has less influencing on the loss and the efficiency of the throat, but, it is still can be found out that the seemly shorter length will decrease the loss. The angle of the straight segment and the placement of the center flap in the straight segment are the factors which influence the capability of the throat. Some examples about the 0.5°angle of the straight segment are given in this paper and proves that the angle can improve the efficiency of the throat. Through the examples of the different placement of the center flap in the straight segment, if putting the center flap backward seemly in the straight segment, it has some advantages to improve the efficiency of the throat. Via 2d examples, five models which have the 600mm×600mm test section are designed in this paper which gives the numerical results.There are many factors which influence the efficiency of throat with choke finger. The aerofoil and configuration of choke finger can be calculated by experiential formulas. In this paper, the NACA0025 aerofoil is chosen for the research. The NACA0025 aerofoil becomes the section of the finger. This paper compares the different bobtail thickness which is an influencing factor to the efficiency of the throat. A rhombus aerofoil is selected in order to get the different influences of aero foils on the throat.According to the results of the numerical simulation, the flap type is more seemly than the choke finger, so, this type of the throat is advised in this paper.