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SUPERSONIC BOUNDARY LAYER INVESTIGATION Aero Engineering Laboratory AOE 4154 Lab Instructor: Dr. Roger Simpson Lab TA: Scott Burger Lab Section: Friday 3:55 – 5:20 Date Performed: December 4, 2009 Student Name: Craig Sossi Student Number: 904512344 Honor Pledge: By submitting this document I pledge that I have neither given nor received unauthorized aid. Craig Sossi Page | 1
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The purpose of this experiment is to investigate the three regions of the boundary layer formed on the wall of the Virginia Tech Supersonic Wind Tunnel. The regions include the Outer Supersonic Region, the Inner Supersonic Region and the Subsonic Flow Region. A probe was traversed at different distances from the wall, and data was recorded. This data was reduced revealing that the probe never reached the Inner Supersonic Region of the boundary layer. While this did not occur, the plots verify flow conditions predicted by theory as the flow approaches a wall. INTRODUCTION Supersonic wind tunnels have been used to study the flow around many objects (often wedges or cones) to determine shock waves and flow patterns. The results of testing have helped engineers design aircraft that can fly efficiently at supersonic speeds. Supersonic tunnels use basic flow theory to create flow speeds of between Mach 1 and Mach 5. The tunnel uses the idea that subsonic flow velocity increases as volume decreases and supersonic flow velocity increases as volume increases. The tunnels store air at high pressure which is then released into the tunnel chamber. As the air reaches the tunnel throat, it is compressed until the flow reaches Mach 1. At this point the flow is then expanded to the desired Mach number, then proceeds through the test section and out into the atmosphere through diffusers or mufflers. These tunnels can also be used to analyze boundary layers at supersonic speeds, either around objects or on the tunnel walls themselves. This experiment will focus on the boundary layer investigation through the use of a small probe. The probe is mounted to a traverse system and will be utilized to measure various flow properties at different locations relative to the tunnel wall. Some flow properties that will be studied include Mach number, density and velocity. There are three different zones that compose the boundary layer and each must be analyzed using different methods. The three zones include: the Outer Supersonic Region, the Inner Supersonic Region and the Subsonic Flow Region. [1] The Outer Supersonic Region refers to the region of the flow where the Mach number is supersonic, the shock is attached and the Talyor-Maccoll equation is valid. [1] To calculate the local Mach number in this region, equation 1 is used. (1) where P c is the cone-static pressure and P t,2 is the Pitot pressure. Once this is obtained, the local velocity can be computed using equation 2 where U is the local mean velocity, M is the Mach number from equation 1, γ is the specific heat ratio, R is the universal gas constant and T t is the total temperature.
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