Jet in a long cylindrical cavity
The flow induced in a long cylinder by an axially discharging round turbulent jet is investigated experimentally, with applications to crude oil degas and refilling of the U.S. Strategic Petroleum Reserves (SPR). A typical SRP cavern holds 10 million barrels with 70 m (diameter) x 2,000 m (deep) and needs to be degassed periodically. This is accomplished by removing oil from the cavern near the bottom and injecting back at the top after degassing, In our experiments homogeneous and stratified jets were used, and both symmetric and asymmetric (with jet radial offset) geometries are considered. It was found that the flow breakups up at a finite distance, does not reach a steady state and vacillates periodically. Digital video recordings, particle image velocimetry and conductivity micro-probes are used to delineate and quantify flow structures. Using the concepts of flow similarity, a model was developed and the results of measurements were parameterized via characteristic length and velocity scales based on the cylinder width and jet kinematic momentum flux. The model was extended to the case of stratified jets and verified experimentally. The scaling laws so developed could be used to extrapolate laboratory observations to SPR flows and help to optimize the refilling process.
Figure 1: Particle streak images showing the jet rotational instability and periodic precession (white arrow) at different times (a-c). See also video in “EFD Video archive”.
Heated horizontal near-surface water jet
The flow induced at the water surface by a submerged heated horizontal turbulent jet is investigated experimentally. Thermal imagery and velocity/vorticity fields near the water surface are obtained simultaneously and this, perhaps, is the first attempt of this kind. The surface temperature in the upper skin layer is measured using research series cooled infrared (IR) camera (FLIR Systems) that works in the mid IR spectrum. The velocity/vorticity fields are measured using commercial (TSI Incorporated) particle image velocimetry (PIV) system. The data obtained are used to examine the detailed structure of the resulting coupled thermal-hydrodynamic fields. To explain the results of observations, a theoretical model is advanced. Practical applications include thermal ship wakes, breaking surface microwaves and penetration of momentum/thermal disturbances from the ocean depth to the surface.
Figure 1: In (a) - typical instantaneous IR thermal image of water surface for near-surface jet. The surface temperature is shown by different colors and temperature traces along two horizontal lines are shown below the image. In (b) - typical averaged near surface velocity/vorticity PIV data. The velocity is shown by small black arrows and vertical vorticity is shown by different colors. Arrows show the nozzle. See also video in “EFD Video archive”.
Wakes and performance of water turbines
Experiments on water turbine wakes and turbine performance were started recently in a large circulating water channel. Using PIV method, first the wake of single turbine will be studied in details with the purpose to optimize the turbine performance. Then the possible influence of turbines positioning in array will be studied. The main idea is to evaluate the optimal energy extraction rates, turbine efficiency and possible environmental influences in turbines array.
Figure 1: Water turbine in a large circulating water channel. Turbine (1) has regulated load and gauges (2) to measure forces in along/across flow directions.
Figure 2: PIV data showing along flow velocity profiles (in m/s) in undisturbed flow (a) and flow with turbine (b).