This research will aid development of the fundamental understanding necessary to determine how a turbulent flow interacts with an eroding or ablating surface. Specifically, the coherent structures within a turbulent boundary layer, for example, trigger and drive the growth of non-uniform surface topography. In turn, the evolving topography influences the coherent structures within the turbulent flow. The coupling between the flow and solid structures can exist under either isothermal or non-isothermal conditions involving heat transfer.
Intellectual Merit: The research team includes investigators at the University of Vermont and the University of New Hampshire. The computational component of the research is aimed at developing a generalized algorithm to simulate the spatially-varying ablation of an initially-smooth surface under heated conditions. Corresponding experimentation will involve acquisition of detailed data to validate the computational model. The model will be based upon the direct numerical simulation methodology which is capable of predicting the fine detail of the flow field as well as the potentially complex surface shape evolution. Correspondingly, the experimental program will utilize, for example, particle image velocimetry to measure the detail of the flow structure, as well as optical methods to capture the surface shape evolution. Both isothermal and non-isothermal conditions will be considered.
Broader Impacts: The coupled dynamics of turbulent flow and surface erosion or ablation is important in applications ranging from high speed flight to latent energy storage. Additional applications include erosion and movement of sand or soil around bridge pilings, and beach erosion. The research will involve a diverse cadre of undergraduate students while a special topics graduate course will address the integration of experiment and computation.
The project work was to use collaborative numerical simulations and physical experiments to investigate how a turbulent flow interacts with an eroding surface. The problem is fundamentally complex yet important in many engineering and natural systems affecting multi-billion dollar investments ranging from coastal real estate to space vehicles. The complexity of the problem is owed to the complex coupling between an eroding material and the eroding flow. Specifically, as the material erodes its surface becomes nonuniform. The surface non-uniformity then changes the flow properties, which then (typically) increases the erosion rate. The net result of this two-way coupling is a runaway effect that makes it extremely difficult to predict the overall erosion rate. Predicting the rate of erosion, however, is critically important for the design and maintenance of erosion control strategies. The numerical work required the development and validation of an algorithm to numerically simulate rapid erosion. Similarly, the experimental work required the design, build, and testing of a thermal wind tunnel facility to study rapid erosion using physical experiments. Combined, these two major accomplishments of this project were used to conduct a systematic scientific investigation to better understand the fundamental physics of rapid erosion. The results of this investigation show that the rate of material erosion is strongly nonuniform in both space and time. In simple flows (e.g., an eroding material in a uniform flow stream), the nonuniform erosion is primarily dictated by interactions between material shape and flow that evolve slow in time. The prediction of erosion rates in these simple flows is generally feasible by applying simplified mathematical models to model the flow and the eroding material. In complex flows (e.g., heated turbulent flows), the nonuniform erosion is primarily dictated by interactions between shape, surface topography, and flow that evolve fast in time. The prediction of erosion rates in these complex flows is not possible with mathematical models alone and requires robust numerical algorithms to simulate these fast interactions. The numerical algorithm developed as part of this project provides the means to predict erosion rates in these complex flows. These simulation capabilities will allow for the design and optimization of mitigation strategies to prevent engineering failures owed to rapid erosion. It also provides a basis to develop simplified models (i.e., less computer costs) to predict erosion rates in complex flows. The project was leveraged to attract and train three graduate engineering students (2 at UNH and 1 at UVM) and four undergraduate engineering students in the integrated applications of experimental methods, advanced numerical computing, and physics based engineering research. All seven students are U.S. citizens. The ability to attract, train, and retain U.S. citizens in engineering is critically important for national competitiveness.
