Kaplan turbine modeling in heliciel draft tube turbine

hydropower by propeller or Kaplan turbine 3/3: Design method

Chapter Summary hydroelectric turbines::

 

  1. Basic Rules
  2. Capture energy

 

The method of calculation and design proposed here, allows you to design the elements of a small hydroelectric power plant. The blade design and calculation of pressure losses using two software tools, Mecaflux for head losses,Heliciel and for the design of the Kaplan turbine. The detailed theories and software tools are available in the appendices sections of this site. Links are definitions of technical terms.

the pressure drop decreases hydraulic power as if the fall height was lower: perte de charge hauteur brute et hauteur nette

    • Gross head height (meters)= elevation between the upstream basin and the downstream basin.
    • Net head height (meters)= Gross head heigh - head loss
Rule 1: Minimizing pressure losses :

What are the energy losses to avoid:

We have seen that the energy losses are important if:

attention aux vitesses élevées dans les conduitesAttention aux changements de sections brusquesAttention aux changements de directions brusques

and that these energy losses will therefore be minimal if:

vitesse lente = faible pertes de chargesVariation de section progressive = faible pertes de chargesChangement de direction progressif = faibles pertes de charge

head losses are calculated simply with the software calculating head losses Mecaflux.

Rule 2: Minimize the cost of partsby concentrating energy:

The price of parts increases with their size, a small turbine and a small guide vanes are less expensive that a large turbine and a large guide vanes.

taille prix helice

To reduce the manufacturing costs of the precious organs collector, as the turbine, the guide vanes, it is advantageous to concentrate the energy in small volumes. To concentrate the energy, we decrease the passage section, the flow rate being constant this increases the speed::section vitesse energie hydroelectrique
The evolution of sections, shows large sections with low losses and a "precious" technical area where the energy is concentrated, so as to reduce the precious organs , despite the head losses that involve high speeds. Changes sections and directions are progressive.
Minimize pressure losses and focus energy are two rules that lead to a respective increase and decrease of the dimensions. This opposition involves compromise between construction cost and performance. The compromise will be found based on the amortization period and the power of installation.

 

Known parameters are the gross height (meters) and volume flow (m3 / h). We have seen that flow through our turbine includes axial component (parallel to the axis of the turbine) and a tangential component (rotation, swirl around the axis of the turbine)..

helice bulbe

Flow rate (m3 / h) given, the section (m²) swept by the propeller will give us axial velocity ( m/sec). The section swept by the propeller is a ring whose external diameter is the diameter of the helix, and whose inner diameter is the diameter of the hub:

la section balayée par l'hélice

axial velocity(m/sec) = Flow rate(m3/sec) / swept section(m²).

 

We will control the axial velocity, by choosing a radius of blade root and blade tip radius, determining the swept section. Recall that the kinetic energy of the axial velocity may be only 60% recovered, so we better advised not to over produce it, so that the proportion of tangential velocity is maximum. We try to create a maximum swept section, the limit will be the cost and size of the system.
To transform the "axial" kinetic energy (relative to the axial velocity) , to couple on the propeller shaft, we will use our turbine blades like airplane wings , which through their lift force will generate torque.The lift causes the rotating blade for generating a torque on the shaft.(Video Software Heliciel)

The lift is a force perpendicular to the velocity seen by the blade. If we are positioned on a blade, the axial velocity, combined with the speed of rotation of the turbine, produces a resulting velocity perceived by the blade, which angle increases with the rotation speed. to almost zero rotation speed, the lift provides maximum torque because it is correctly oriented, but a lot of fluid passes through the turbine without transferring energy to the blade. at high rotational speed, the lift has an angle, generates less torque, but the amount of fluid passing through the propeller without exchanging energy decreases.There is therefore an optimum rotation speed which combines the direction of the forces of lift (and drag) optimally...We will not detail more here this principle (for more on this turbine operation), But we will retain the axial fluid stream generates a torque on the turbine shaft, with the lift of the blades.
In this video, the fluid enters the impeller with an axial velocity without any tangential component of rotation about the axis..

 

By reaction principle, the torque generated on the shaft, generates a rotation of the fluid in the opposite direction to the speed of rotation.This is the "induced tangential" velocity generated by the capture of the axial flow.
Considering the speed of the fluid, such as an amount of energy, we can say that any movement out of our turbine shows the energy that escapes us. The rotation of the fluid (tangential velocity) generated by the reaction torque of the turbine is energy lost. This energy would be captured, if at the output of the propeller no tangential velocity was seen..

 

So far we have considered only the axial flow generated by the flow, it is time to attend to the tangential velocity, that the guide vanes can generate, using load height, et voir comment nous allons capter cette vitesse tangentielle introduite en entrée de turbine.
We have seen that our propeller generates a tangential velocity induced by transforming the axial velocity , to torque on the propeller shaft .This induced tangential velocity is opposite to the rotational direction of the propeller shaft. Any output speed is a loss, if we enter into the turbine, a tangential velocity equal and opposite to the induced tangential velocity at the output propeller,the sum of two opposing tangential velocities will give a zero output tangential speed. We could say that we have captured all the tangential kinetic energy!!

In this example, at the turbine inlet, the tangential velocity is zero. at the outlet, the fluid received by the torque reaction of the turbine, a tangential velocity energye, that will be lost

In this example, at the turbine inlet, a tangential velocity is given. at the outlet, the fluid received by the torque reaction of the turbine, which rectifies and cancels the tangential velocity introduced.. The energy of the tangential velocity, introduced, is captured

To produce the tangential velocity of the vortex entrance, the guide vanes uses hydraulic power, if it produces too much, this translates into a tangential velocity at the turbine outlet, uncaptured, so wasted. The calculation of the turbine guide vanes are closely linked by the induced tangential velocity of the turbine. The balance between the tangential velocity produced by the guide vanes and the tangential velocity induced by the turbine will be achieved if: To achieve this balance, the method proposed here, uses the calculation of the turbine according to the expected rate (assisted by HELICIEL software), to obtain all the data that allow us to scale the other organs (guide vanes, draft tube, pipes sections )

lele tourbillon genéré par le distributeur entraine augmente la vitesse de rotation de l'hélice

Method of calculation and dimensioning of the elements of a hydraulic plant Software equipment used:
Input data used:
  • Load height (meters) (difference between the upstream and the downstream basin area) = 4.3 meters
  • Volumetric flow of the site (m3/sec) = 12 m3/sec
  • Blade tip radius = 1000 mm
  • Radius at the blade root = 600 mm (60%)
  • width (chord) at the blade root = 738 mm
  • width (chord) at the blade tip = 1138 mm
  • number of blades = 4
results output
  • Crossing speed of the turbine and the operating point
  • Optimal rotational speed
  • Tangential velocities to introduce with the guide vanes
  • Assessment of depression generated by darft tube
  • Total shaft power, in the event that the guide vanes introduced the tangential velocity calculated
  • 3D model and definition of twisting, the IGS format for the creation of the blade
Design phases:

 

We will see this in detail in the tutorial example design of a small hydroelectric plant.

Chapter Summary hydroelectric turbines::