In this work, the structure and dynamics of a shock train are studied experimentally using a direct-connect isolator model with a nominal inflow Mach number of 2.0. The experiments mimic the flow in a high-speed air-breathing engine, where the shock train is responsible for slowing and compressing the flow prior to the combustor. Quantifying and understanding the properties and processes of the shock train is critical to the development of more predictive modeling tools for high-speed engine design.

In the first part of this work, schlieren imaging is used to study the shock train structural transition from oblique to normal as the pressure downstream of the isolator is increased. Time-averaged pressure measurements are used to quantify how this process impacts important isolator design properties, including the length and pressure of the shock system. These results indicate a highly three-dimensional structure which is confirmed using stereo PIV measurements.

The second and primary contribution of this work is the development of a model that explains why the shock train is inherently unsteady even with approximately constant isolator boundary conditions. Cross-spectral analysis of pressure and shock position fluctuations are used to identify a system of perturbations that interact with the shock system. Oil flow visualization and PIV are then used to uncover the physical structure of the perturbations and the fluid phenomenon that generates them. The unsteadiness model introduces a possible mechanism that explains how downstream disturbances impact the shock motion. To examine this further, low frequency downstream forcing is applied to the system and the resulting shock train response is investigated using a combination of schlieren and pressure measurements. It is found that the response of the shock system depends on the rise time and magnitude of the downstream disturbance.


Dissertation Committee:

Chair: Asst. Prof. Mirko Gamba
Cognate Member: Assoc. Prof. Eric Johnsen
Members: Prof. James Driscoll, Prof. Venkat Raman, and Dr. Jeffrey Donbar (Air Force Research Lab)

Publication list:

1. Hunt, R. L. and Gamba, M., “Shock train unsteadiness characteristics, oblique-to-normal transition, and three-dimensional leading shock structure,” AIAA Journal, 2017, DOI 10.2514/1.J056344.

2. Hunt, R. L. and Gamba, M., “On the origin and propagation of perturbations that cause shock train inherent unsteadiness” submitted for consideration to Journal of Fluid Mechanics.

3. Hunt, R. L., Edelman, L. M., Gamba, M., “Scaling of pseudoshock length and pressure rise,” 56th AIAA Aerospace Sciences Meeting, 2018.

4. Hunt, R. L., Driscoll, J. F., and Gamba, M., “Periodic forcing of a shock train in Mach 2.0 flow,” 55th AIAA Aerospace Sciences Meeting, 2017.

5. Hunt, R. L., Driscoll, J. F., and Gamba, M., “Unsteadiness characteristics and three-dimensional leading shock structure of a Mach 2.0 shock train,” 55th AIAA Aerospace Sciences Meeting, 2017.
6. Klomparens, R. L., Driscoll, J. F., and Gamba, M., "Response of a shock train to downstream back pressure forcing," 54th AIAA Aerospace Sciences Meeting, 2016.

7. Morajkar, R. M., Klomparens, R. L., Eagle, W. E., Driscoll, J. F., Gamba, M., and Benek, J. A., "Relationship between intermittent separation and vortex structure in a three-dimensional shock / boundary-layer interaction," AIAA Journal, Vol. 54, No. 6, 2016.

8. Klomparens, R. L., Driscoll, J. F., and Gamba, M., "Unsteadiness characteristics and pressure distribution of an oblique shock train," 53rd AIAA Aerospace Sciences Meeting, 2015.

9. Morajkar, R. M., Klomparens, R. L., Eagle, W. E., Driscoll, J. F., and Gamba, M., "Flow separation associated with 3-D shock-boundary layer interaction," 52nd AIAA Aerospace Sciences Meeting, 2014.