Volumetric Pressure Reconstruction around a Submerged Obstacle Using Stereoscopic Multi-Planar PIV with Applications to Hyporheic Flow Modeling

Experimental quantification of volumetric, fluid pressure fields is desirable for many applications, including hyporheic flow modeling for predicting temperature and dissolved gas concentration distributions in riverine environments. Experiments were conducted in a straight, recirculating flume to quantify the pressure distribution around a vegetation stalk, modeled as a 1-cm-diameter, 10-cm-tall, rigid cylinder. To match the cylinder’s refractive index (1.365), 15% in weight of MgSO₄ (Epsom salt) was dissolved into the flume water. Stereoscopic PIV measurements of transverse-normal planes were collected at 24 transverse locations, including five which intersected the cylinder. The velocity field spatial resolution in the vertical and longitudinal directions was 1 mm. Pressure gradient fields were generated using the Reynolds-Averaged Navier Stokes equation. A 2D omnidirectional integration approach was used to reconstruct the pressure distribution in each plane. Low connectivity over the cylinder and in the transverse direction and limited boundary condition information pose challenges when reconstructing the pressure distributions in planes intersecting the cylinder in deep flow cases. A new reference pressure correction method, utilizing the transverse pressure gradient, was developed to account for these challenges. The resulting pressure distribution near the bed set the boundary condition in MODFLOW software which models flow through the porous flume bed.