River or Tidal Current “Flutter Fin” Counter-Oscillating  Adaptation of Flo’pump for Tidal or Hydro Power

    The Flo’Pump can be inverted for a powerful oscillating water current mill below a small floating platform with the blade and pump the only submerged moving parts. The weight in water of the inverted fin is its own roll pendulum and also provides good pitch stability without wave excitation by a high pitch metacenter platform. The semicircular swept area better covers a typical small channel than the circular or rectangular swept areas of turbines especially for mimimum obstruction of navigation from a surface base. The swept area and so power is much greater for a given blade and structure length (cost) than the Stingray or Pulsegen configurations which ignored Econologica’s experience. The high speed ratio part of the cycle is at the deepest depth so cavitation and surface ventilation will not occur as they might on insufficiently submerged rotors. The large blunt fins  moving at modest speed ratio will not damage red herrings whose mortality from from the sharp fast spinning and translating propellers of boats is accepted anyways.

   Unlike rotors oscillating fins do not wrap weeds or errant ropes to jam. Nor need there be any bearings at all in the silt-laden if not corrosive stream. Bow and stern anchors on bridles give fairly tight positioning for nearby shipping with no wrapping or excess movement of  the output line. It is better to have well marked visible audible presence and warning rather than being hidden underwater at the mercy of (dragging) boat anchors and commerical fishing gear. Units can be built at a small shipyard, pretested and towed to a site for easy installation in one tide window, and just as easily moved.

To greatly  reduce the reaction requirements of the floating platform, two fins would counteroscillate  Since a single wing extracts at most ½ the Betz limit, there is about the same power available for the second fin, especially if the solidity is reduced a bit over the windmill wing.  With the slow buildup of the tidal stream, coupled cam ramps give the static blades opposed angle of attacks to start. When they incline sufficiently either pitch arm falling off the end of its ramp makes the ramps unbalanced so the other arm is released as well, and the oscillation begins. The ramps are not further contacted  as feathering is not needed  unlike in high winds. The scissor mechanism is prevented from inverting by cables from one scissor joint through pulleys on each side back to the other scissor joint. The blades can be installed level with the surface and returned to this position for periodic cleaning in neap slack tides. In operation the swing varies from say ± 45°  to 75 ° limited by the big increase in stroke volume after 60°  as the pump rod is depressed far enough to drive the large upper second piston. Shock is more easily avoided by small airsacs below the pistons than by stainless bumper springs. 

   The Flutterfin’s prime niche would be pumping water, either ashore for use or to generate electricity off-grid. As in Wing’d Pump generation water would be pumped into a large high pressure tank against  trapped ( isothermal) air. A used ‘propane’ tank (rated at 215 psi new)  could stand vertical with a silicon oil film floating on top of the water to reduce air absorption and corrosion. This could be efficiently converted to constant voltage and frequency electricity  on demand by a small impulse wheel close to the hydropneumatic tank. Testing is planned of a cheap arc valve that swings to vary the jet orifice area with little hydraulic  power or flow loss or control resistance. For the time being, not quite as fine a control is to have multiple fixed nozzles on the same Pelton wheel each turned on by energizing a 150 psi (household) irrigation solenoid costing about $20 and using about 5W. By having say 4 nozzles each twice the previous in flow area, different combinations of on and off give 16 equal steps in flow rate. The control would 'count' through these to keep the generator rpm constant and output voltage and frequency constant as the load varies. Because the waterflow is from airpressure and not water height, fast control without water hammer is feasible unlike in micro-hydro where standby heating "loads" (of high waste)  must be switched on and off.  The system cost should be very competitive with underwater turbines charging battery banks with much smaller system losses.

   The model wings are galvanised or stainless steel sheet with a pipe spar/axle. Foam fills the tail volume and cement the nose. At full scale production reinforced concrete and foam seems possible using expansive cement for its watertightness and self-stressing against the reinforcement. The pitch counterweight to achieve near pitch weight balances will be much smaller than in the windmill case as there the wing CG must be ahead of ¼ chord but here at mean specific gravity of 2 say, the CG just needs to be midway between the CB and the axis at 22% chord for no net moment. 

   The Flutterfin like the Wing’d Pump self-articulates  and does not have complicated underwater pitch articulation mechanisms like the PulseGen. Underwater (HA) rotors have  bearings, gearboxes, and  generators submerged in seawater. If the seals fail, these expensive components will be ruined by corrosion and the oil will pollute the water. So the component, installation foundation and maintenance costs are much higher than the Flutterfin. Of the rotor designs to feed the grid  the best option would seem to be a Vawt cantilevered below a floating ‘endplate’ platform, synchronously started from the grid, possibly even from the tide tables. The tidal current power spectrum is usually sufficiently narrowbanded that the Vawt’s narrow operating peak won’t lose much and stall can be avoided just beyond the max tidal speed.  Again underwater bearings  can be entirely avoided though not underwater cleaning. Foil fouling is critical given the Vawt’s high drag losses. Most tidal windmill proposals seem totally blind to the severe fouling and corrosion problems of saltwater and are deliberately blind in submerging everything beyond visual monitoring and visual avoidance by (fishing) boats and anchoring ships. Our well experience is that working blind in a corrosive environment is a major development and eventual maintenance handicap.

  There are several potential ways to prevent clogging of the pump system with marine growth. Firstly as with the fins all external surfaces at least would be coated with antifouling paint. Secondly the outside of the pump would be cleaned with long poles from the surface though not as effectively as the wings brought to the surface.  Just before an extended slack tide, the pump system could be fed with a watersoluble biocide which would then get pumped into the pipeline and dwell and kill internal growth during the typical 2 or 3 days of insufficient currents, but then breakdown before output at the shore station. Chlorine generated from the seawater is used in seawater cooling systems. Less frequently in such a slack tide interval  the pipeline would be rotor-rooted from shore  and the entire pump could be replaced with a spare. The removed unit would be disassembled ashore for thorough internal cleaning and inspection if not replacement of the piston cup seals. A complete solution  would always be a closed pump above water with dual pipelines of hydraulic oil, preferably a benign natural type for the worst case scenario of a spill.