59690 - Reconstruction of Temperature Distribution for a Turbulent Free Jet Using Background Oriented Schlieren 

Background oriented schlieren (BOS) has been shown to be an excellent tool for qualitative flow visualization, and more recently, literature has shown that the technique can be expanded to yield quantitative measurements as well. In this study a BOS setup is built to construct the temperature distribution of a heated turbulent free 12mm diameter jet. A high spatial resolution camera is used to view a black and white speckled background plane through the heated free jet in question. Viewing through the variable density medium results in the apparent displacement of points on the background plane. By comparing control images captured before the flow is introduced with images of the distorted background due to the flow, the amount of apparent displacement at each point can be measured utilizing a cross correlation algorithm. Once this displacement field is obtained, a new algebraic algorithm is implemented to reconstruct the refractive index of the center plane of the jet. Then, the Gladstone-Dale and ideal gas relations are used to calculate the temperature of the center plane. Reynolds numbers based on the jet diameter is varied from 5,000 to 15,000 along with temperatures in the range of 100C to 250C. Reconstructed temperature distributions are validated using k-type thermocouple measurements. In each case, the system is allowed to reach steady state ensuring uniform conditions for thermocouple and BOS data acquisition.  Further, this technique has the potential to be used to determine the temperatures in open and optically accessible closed reactive flows. Having information about near wall temperature in closed reactive flows will give insight into wall convective heat transfer characterization and also help benchmark combustion based numerical models in applications such as gas turbines.