Flows of environmental significance abound in nature across a broad range of scales, from the macro- to
micro-scales. These flows are oftentimes key drivers of physical and biogeochemical processes on Earth and thus have a tremendous impact
on the environment. While direct observations of such processes would be preferable, many of them occur in natural systems for which the
environmental conditions limit or completely impede access via modern flow diagnostics due to geometry and/or coexistence of multiple phases
(solid, liquid, gas and/or multiple of each). Because of the broad range of scales typically present in such flows, modeling at small scales
is required so that predictive simulations are possible. It is at these scales where experiments can inform the development of models that
accurately reflect the underlying physics of such processes which, in turn, would yield more reliable predictions at system scales.
This lecture will highlight two model problems in this regard, specifically environmental flow systems that challenge flow interrogation with optical diagnostics: turbulent flow associated with interacting barchan dunes at the macroscale and the pore-scale dynamics of CO2 injection into geologic storage sites at the microscale. Novel implementations of PIV methods are being used to overcome these challenges. In the case of flow associated with interacting barchan dunes, we are leveraging refractive index matching coupled with planar and volumetric PIV to access the near-dune flow physics that is inaccessible otherwise. In the case of geologic CO2 sequestration, we are capturing for the first time the multi-phase flow dynamics of supercritical CO2 and resident water in heterogeneous rock formations at reservoir pressures (80-100 bar) utilizing fluorescent microscopy coupled with microscopic PIV. The details of these unique measurement approaches will be discussed as will the new insight gained into the flow physics that govern these environmental flow systems.