Hydraulic Water Turbines

Impulse Wheels, Sort Of.....Banki Mitchell Turbines

The present more widespread use of the cross-flow turbine is largelydue to the efforts of the Ossberger concern in Weissenburg, Bavaria, whoadded a number of original ideas to Michell's design, based on their ownresearch work. The various stages of this steady development are coveredby world patents. Thousands of these Crossflow Turbines have been buildby Ossberger.

The main characteristic of the cross-flow turbine is that it usesbroad rectangular water jet of water that travels through the turbine onlyonce but travels across each rubber blade twice, once in each direction.The water flows through the runner blading first from the periphery towardsthe center. and then. after crossing the open center space. from the insideoutwards. This machine is therefore a turbine with two velocity stages,the water filling only part of the runner at any one time. As far as energyutilization is concerned, the use of two velocity stages provides no immediateadvantages. The arrangement represents, however. a very skillful designwhich removes the water in a simple manner after it has passed throughthe runner without producing any back pressure. The addition of a drafttube to the cross-flow turbine  represents  an  implementedby Ossberger to enhance the Turbine's performance.  Ossberger usesa air valve in the draft tube to help regulate the head by introducingair in the draft tube.

The machine is normally classified as an impulse or free-jet turbine.In it's original design this classification is not strictly correct sinceit was designed as a true constant-pressure turbine. A sufficiently largegap was left between the nozzle and the runner to ensure that the jet enteredthe runner without any static pressure. There was also sufficient spacein the runner itself to allow the jet to expand freely sideways. Duringthe passage through the first stage conditions were therefore essentiallythe same as in the much older Zuppinger free-jet turbine. However, thepresent design in which the nozzle is shaped to follow the runner peripheryclosely giving better results. At full or nearly full gate there is a slightpositive pressure in the gap. This can readily be demonstrated by measuringthe flow passing through the machine with and without the runner at a constanthead and gate. The flow is found to be greater if no runner is fitted inthe turbine (experiments carried out by Prof. F. Euler at the Hagen TechnicalCollege). The deviation from the constant-pressure principle must of coursebe taken into account in closing the gap between nozzle and runner. Itis only during the second passage of the water through the runner bladingthat the usual constant-pressure condition applies.

The Ossberger Crossflow was extremely popular in Europe a few yearsago.  They built in excess of 4000 commercial Crossflow Turbines. They ranged to 600 feet of head, 400 CFS @ 30 feet of head and power outputsto 2500 HP.

TheCrossflow Turbine shown here belongs to John McMillian. John has lengthenedto runner to 66 inches to accommodate a head of 2.75 feet using 5.5 CFSof water.  He generates about 400 watts with a 14 volt modified Delcoautomotive alternator. John has lots of construction details, picturesof his installation at his Web Page.
 Visit John's Web PagePINECREST: An Adventure Living Off The Utility Gridfor more details on his setup as well as pictures of his installation.

Impulse Wheels

Pelton Wheels

Theimpulse turbine are medium to very high head machine.  They come in a variety of sizes from about 4 inch diameter to monsters like the 30,000Hp Allis-Chalmers pictures here.  Compared to the Frances turbinethe impulse wheels use a lot less water but operates at much higher headpressures.  The pelton Wheel is the best example of an Impulse Wheel. It operates by one or more jets direct water into the center of the bucketsaround the parameter of the runner.  Power is derived form the forceof water at high pressure hitting the passing buckets, hence the term "impulse"turbine.  The other type impulse turbine is the Turgo Wheel. Even though they look quite different from each other in principle theoperate the same.  In the Pelton wheel water is directed into theradial buckets, 90 degrees to the shaft.  In the Turgo Wheel the bucketsare replaces with U shapes blades arranged radially on the "face" of therunner.
High Head Turbines.

Here's the basic technical explanation of how the Pelton Wheel works. The vector diagram shows a horizontal section through one of the bucketstaken on a plane passing through the axis of the jet. The bucket movesin a circular path, but for the present purposewwe Will assume its pathto be a straight line, coincident with the jet's axis, and that its velocity,U, is constant. Twosuccessive positions of the bucket are shown, together with the path ofthe water as it flows over the bucket's surface. The path of the water,relative to the bucket, is shown In dotted lines. The water leaves thebucket with a relative velocity, v2, whose direction is tangent the bucketsurface at the point of exit. The angle between v2 and the jet's axis,commonly called the bucket angle, is designated by B. Due to thecombined motion of the water over the bucket and of the bucket throughspace, the actual path of the water is that shown by the full lines,the water leaving the bucket with an absolute velocity, V2, at an anglea, with the jet's axis. It is to be noted that V2 is the vectorsum of v2 and u; that the absolute path of the water has an easier curvaturethan the surface of the bucket, and that the angle, a, through whichthe water is deflected, is much less than the bucket angle, B.
The velocity of the water in the original direction of the jet isreduced from V1 to V2 cos (a) and the component, in this direction,of the pressure exerted by the jet on the bucket is:
 
 

This component is the force which causes the bucket to move withuni-form speed against the resistance supplied by the load on the turbine.The value of M1 is that mass of water which each second of time passesover the bucket. The total of the separate forces simultaneously actingon each live bucket can be obtained from the above equation if we changeM' to M, since the combined masses flowing per second over the active bucketsequals the mass, M, discharged per second by the nozzle. We have, therefore:Px=(Qw/g)*(V1-V2*Cos(a)
as the value of the turning force applied to the wheel and, sinceit moves u feet per second, Pxu becomes the work done in one second orthe power input to the shaft. It is greater than the power output fromthe shaft by the amount lost in bearing friction and by windage. (g) isthe gravitational constant of 32.2.Pictured below is vector diagram for a Pelton Wheel.Note: If blew off the above as boring then gogo back & read it again until you understand it!!!  While writtenspecifically for the Pelton Wheel, the the interaction of V1 (Water velocity)V2( Velocity of the water as it exits the turbine) v2 (relative velocity)& u (peripheral speed of the runner) are the basis for ALL turbomachinery operation.
 
 

Impulse Wheels

Turgo Wheel

Another type of Impulse machine is the Turgo Wheel. It is rare to find them   in commercial power plants but theyare quite popular for low voltage DC systems using a battery bank and aninverter.  A lot of these systems are sold pre-packages (plug &play) and use an automotive alternator , regulator & battery(s). In a few cases where higher power is required an or an AC is generated,they're use with an alternator or an asynchronous generator.  While the majority of the Turgo systems I've found in Internet searchesare of the 600 to 2000 Watt varieties I have found some in the 6 KW rangealthough I'm told a few are in the Megawatt range. Both the Pelton &Turgo wheel, depending on manufacture come with either cast bronze or plasticrunner wheels.  There is absolutely no reason not to take advantageof the lower cost plastic wheels.  Modern plastics are very durableand ware quite well an should present no problems in installed properly.In some installations they might require a flywheel but that more thenlikely be a "hi-end" system and would be taken care of for you.

These Turgo Wheels do look a bit strange if your used to Frances& Pelton machines.  If the Turgo Wheel were mounted with the shaftvertical, then the water jets would be aimed downward but tilted in thedirection of rotation.  However the water exits the wheel almost exactlyas a Francis Turbine would.
 

Reaction Turbines

Francis Turbine

This is the one that killed the Water Wheel.  When it comesto commercial Turbines, there are and have been more of these Turbinesmade then all the others combined.  The Francis Turbine dominateslarge Hydro-Electric plants all over the world. It has only one rival inand that's the Kaplin.

Very High Head Runner and Turbine Housing

Reactions turbines like the Francis & Kaplin turbines rely on the weight of thewater passing through them to produce their power.  The behemoth pictured here is a 50,000 HP job.  They are relatively low speed devices &their water usage can be from moderate to huge.  As far as Head pressuregoes they run the full gamut from 2 or 3 feet to over 1000 feet. There are thousands of Francis turbines throughout the world today. Several hundred of these are at the base of dams you see at the many lakesaround the country.  These Francis turbines typically have an operationhead of 60-120 feet or so.  Their power output is in the range ofmegawatts.  Thousands off low to medium head Frances turbines havebeen installed all over the world doing a variety of functions.  Mostlythey powered generators for farm & industrial use.  However manyproduced direct mechanical power for things like saw mills, grist mills,ice houses, machine shops etc.  In the late 1800's & early 1900'eon the east coast when textiles were in their hay-day, hundreds of textilemills were scattered along slowmoving but large rivers.  Remnants of these mills can still be foundtoday, some still completely intact.  They usually built canals toharness the rivers flow and divert absolutely hugs quantities od waterinto low head Frances turbines to power these mills.  Virtually everypiece od equipment in these mills were powered by one Frances turbine. The turbine would drive literally hundreds of "jack-shafts" through themill.  Each jack-shaft would in turn supply power to several machinesvia flat belting.
 

Thereare however a few ultra high head scattered throughout mountain regions. The 1 megawatt Nantahala Power Plant near Bryson City NC is the most famousof these  high head Frances turbine.  The Nantahala plants watersupply is miles & miles away.  The water flows through severalmiles of tunnel & steel penstock 8 feet in diameter.  The operating head is a whopping 1000 feet!  The runner of the Nantahalaturbine is very narrow (short) & very wide when compared to a 100 foothead Francis at a dam site.  The Frances runner pictured above istypical of typical proportions for a medium head (100 foot) runners.
 
 

Diagram of the "First Frances Turbine"  Low head.  Not that it does nothave compound curve blades like it's descendants.
 
 

Reaction Turbines

Kaplin

Thisis the competition for the  Francis.  It's used mostly at damsheads under 100 feet.  It use huge quantities of water.  Thenewer Kaplin like the read one shown are extremely efficient over a rangeof flows because the blades are adjustable to accommodate lower flows,something no other turbine can claim.
 
 

Reaction TurbinesOther types from the past

Reactions turbines like the Francis & Kaplin turbines rely onthe weight of the water passing through them to produce their power. They are relatively low speed devices & their water usage can be frommoderate to huge.  As far as Head pressure goes they run the fullgamut from 2 or 3 feet to over 1000 feet.  There are thousands ofFrancis turbines throughout the world today.  Several hundred of theseare at the base of dams you see at the many lakes around the country. These Francis turbines typically have an operation head of 60-120 feetor so.  Their power output is in the range of megawatts.  Thousandsoff low to medium head Frances turbines have been installed all over theworld doing a variety of functions.  Mostly they powered generatorsfor farm & industrial use.  However many produced direct mechanicalpower for things like saw mills, grist mills, ice houses, machine shopsetc.  In the late 1800's & early 1900'e on the east coast whentextiles were in their hay-day, hundreds of textile mills were scatteredalong slow moving but large rivers.  Remnants of these mills can stillbe found today, some still completely intact.  They usually builtcanals to harness the rivers flow and divert absolutely hugs quantitiesod water into low head Frances turbines to power these mills.  Virtuallyevery piece of equipment in these mills were powered by one Frances turbine. The turbine would drive literally hundreds of "jack-shafts" through themill.  Each jack-shaft would in turn supply power to several machines via flat belting.
 

There are however a few ultra high head scattered throughout mountainregions.  The 1 megawatt Nantahala Power Plant near Bryson City NCis the most famous of these  high head Frances turbine.  TheNantahala plants water supply is miles & miles away.  The waterflows through several miles of tunnel & steel penstock 8 feet in diameter. The  operating head is a whopping 1000 feet!  The runner of theNantahala turbine is very narrow (short) & very wide when comparedto a 100 foot head Francis at a dam site.  The Frances runner picturedabove is typical of typical proportions for a medium head (100 foot) runners.