In-situ Pressure Measurements in Gavunda Hydropower Tunnel during Full Operation

Hundreds of miles of Hydropower tunnels have been excavated in Sweden the last four decades. They are of utmost importance to the hydropower industry, yet they are frequently subjected to rock falls or worse (Bratveit, et. al., 2016), in addition, information regarding the flow situation inside the tunnels are scarce. Simulations within Gavunda water tunnel has shown a strong correlation between changes in cross-sectional area and pressure (Andersson, Hellstram, Andreasson, & Lundstrom, 2019). Thus, conclusions about the cross-section can be deduced from measuring the pressure inside water tunnels. These results have also been experimentally validated (Aberle, et. al., 2020). However, measuring inside water tunnels is an arduous process, inaccessibility and a generally inhospitable environment makes use of expensive ROV's not preferable. In this project the design of an autonomous probe, which will sample the pressure inside the tunnel, has been evaluated. The probe will be small, easy to use and cheap in order to be easily replaced in case it is lost or destroyed during operation. Inside the tunnel the sensor will move laterally due to local flow disturbances, these movements will introduce noise in the pressure measurements. In order to account for this noise the probe has been equipped with an BN0055 Inertial Measurement Unit (IMU). The IMU allows for 9-degrees of freedom measurement of acceleration, containing an accelerometer, a gyroscope and a magnetometer. Using the IMU, the pressure variations due to movement can be separated from the pressure variations due to the change in cross-section.