Intake Vortex Formation and Suppression at Hydropower Facilities
At what water depths do intake vortices form at hydropower facilities? Is an intake vortex dependent on individual
penstock flow or the total flow passing through the system? How much efficiency is lost for a generation unit with
the presence of a vortex? Are vortex suppressors capable to arrest development without impacting generating
unit efficiency? How dependent on site specific geometry and operating conditions is the formation of vortices?
A vortex is formed as water accelerates through the narrow opening of an intake structure below the surface of
the water. As the water flows through the structure, it will begin to spin due to the forces acting on it and will
create higher water surface elevations on the perimeter with a depression in the center. As the vortex enlarges,
the central area continues to depress, and can form different vortex types that represent from a surface swirl to a
stable hollow air core. Conditions that impact the creation of a vortex are submergence, flow rate and the
geometry of the intake structure.
Vortices are a major source of air entrainment, and can lead to reduction in turbine efficiency, decreased flow
rates, pulsation ,pressure surges, and vibration issues. They can also allow more surface debris to be pulled
underwater and become caught on intake structure trash racks which can further reduce efficiency.
Reclamation is the second largest producer of hydropower in the United States, and has powerplants operating at
53 dam sites in all 5 of Reclamation's Regions as well as low head installations at irrigation canals. With current
drought conditions across much of the western US, powerplant operators are concerned about the potential for
falling water surfaces to create vortices at intakes. While there are standards of practice for current designs, many
older structures may not have been designed to the same level or the facility is forced to operate outside the
design criteria where vortex formation may be poss
Need and Benefit
Powerplant operators are responsible for meeting hydroelectric demands at their facilities, and the presence of air
in the flow passing through the generating unit can decrease overall efficiency as well as create fluctuation of the
power output which makes regulation more difficult. There are also long term detriments to intake vortices of
pressure surges on the intake structure and outlet works.
This scoping proposal will look at conditions that have created vortices at Reclamation powerplant facilities and
will compare these conditions with recommendations from contemporary research. Investigation of generalized
guidelines for both powerplant and pump intake designs will be considered, as will the potential benefit of vortex
suppressor installation at the facilities. All of Reclamation's regions will benefit from knowledge gained by
understanding conditions that can create powerplant intake vortices.
Contact the Principal Investigator for information about partners.
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Intake Vortex Formation and Suppression at Hydropower Facilities (final, PDF,
By Kent Walker
Publication completed on September 30, 2016