HydroAir

TM

Variable Radius Turbine
Dresser-Rand is developing alternative energy sources, including
marine renewable (wave) energy.

Oscillating Water Column Technology
Oscillating Water Column (OWC) technology is the most successful and extensively
studied technology for extracting energy from ocean waves. OWCs can be
located on the shoreline, nearshore or offshore. Incoming surface waves induce
an oscillating flow of air within the chamber which, in turn, flows backwards and
forwards through an air turbine installed in a duct connecting the chamber to the
atmosphere. The turbine converts this air movement into electrical energy.
The challenge of OWC technology is to achieve satisfactory efficiency over
a wide operating range, considering that the airflow not only varies between
zero and 100 percent, but also changes direction (shaft rotation must also be
maintained in the same direction).
Dresser-Rand has patented a Variable Radius Turbine (VRT) called HydroAir.
The turbine is constructed to withstand the rigors of a marine environment
using a combination of stainless steel, aluminium and reinforced composites to
resist corrosion. In addition, it offers the following benefits when compared to
other turbines being used for wave energy capture:
• Above average efficiency
• One moving part - the rotor
• Lower rotational speeds than competing turbines
• Currently designed up to 500 kW
• Wide operating range
• Self-starting
• Reduced noise

Oscillating Water Column Device.

The VRT design comprises two sets of static guide vanes located on either
side and of a larger diameter than that of the rotor. These vanes are
connected by a shaped duct to provide a route for the (inlet/outlet) airflow. Air
enters the duct at a relatively low velocity and acquires a swirl motion as it
passes through the inlet guide vanes. The air then accelerates as it passes
down the narrowing duct towards the turbine rotor. The air drives the rotor, and
then decelerates as it travels back through the expanding duct before passing
over the outlet guide vanes. The process is repeated (in reverse) for the next
wave cycle.
In comparison with both Wells turbines and conventional impulse turbines,
the HydroAir turbine solution offers a step-change in efficiency and operating
range. The HydroAir turbine achieves its remarkable performance with fixed
blade geometry, providing the reliability that is critical to the commercialisation
of wave power.