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Abstract: The paper is devoted to parametric design of reaction hydraulic turbines draft tube. Knowing the hydraulic turbine runner data and location there are determined the draft tube length, cross sections geometry and shape. The efficiency (recovery coefficient) of this divergent special pipe in function of geometric and kinematic parameters is established. The analytical formulas obtained are useful for design and local hydrodynamic flow numerical analysis. The obtained design formulas fits for power plants with one or small number of hydro-units or for micro-power-plants.

Keywords: hydraulic turbines, draft tube, geometric and hydrodynamic parameters, draft tube design and optimization

(ProQuest: ... denotes formulae omitted.)

1. Introduction

Draft tube is an important part of the Francis and Kaplan hydraulic turbines. It's roles are to recover the exit hydraulic energy of the water from the runner and to install the hydraulic turbines in an convenient position ( from economical and non-cavitational point of view).

Researches about hydrodynamic flow in draft tubes are present in the last IAHR Symposiums and Conferences ( Beijing 1994, Valencia 1996, Singapore 1998, North Carolina 22000, Lausanne 2002, Stuttgart 2003,..,Timi§oara 2010). A lot of books and articles ( authors like N. Kovalev, S. Granovschi, J. Raabe, ed. R. Krishna, J. Giesecke, A. Bärgläzan, and reviews like Trudî VIGM ) give design statistical data and empirical dimensions about draft tube geometry and operation.

List of symbols

D - diameter of draft tube cross section,

Llength of the draft tube,

h - highness of draft tube diffuser,

I - breadth of the draft tube diffuser,

aangle of the draft tube divergence,

Az / D - draft tube relative deepness,

ß - elbow angle,

R - elbow curvature radius,

Hssuction head of the hydraulic turbine,

a - runner vertical height in respect of draft tube entrance,

b - draft tube exit depth in respect of the tail water level,

A A / L - gradient of cross section area along the draft tube,

v - mean axial velocity of the flow in the draft tube,

Ht - hydraulic turbine head,

Q - rate of flow,

p - pressure,

2. Draft tube parameters

The draft tube is a special divergent pipe in which it is necessary to maintain the attached flow inside in order to obtain a...

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