Three-dimensional flow analysis through an axial turbine stage

Other Title(s)

تحليل الجريان الثلاثي الأبعاد خلال مرحلة توربين محوري مع تداخل الريش الثابتة و المتحركة

Dissertant

Yunus, Sudad Isam

University

University of Technology

Faculty

Department of Mechanics and Equipments Engineering

University Country

Iraq

Degree

Ph.D.

Degree Date

2006

English Abstract

Fully three-dimensional periodic flows through an axial turbine stage of nozzle vanes and rotor blades are studied numerically by solving the time dependent three-dimensional Euler equations with time marching method.

The phase relation of nozzle and rotor flows and the related blade-row interaction are accounted for the time-space domain.

The flow was initially treated as two dimensional and then extended to fully three-dimensional, compressible, unsteady in viscid calculation, by using a finite volume cell structure with the flow variables stored at each cell center.

The established method of numerical calculation makes a practical contribution to predict actual flows through a turbine stage of stator and rotor that have (62) stator vanes and (68) rotor blades.

Simulating programs were constructed to predict the tow field properties through the whole axial turbine stage.

The two dimensional programs were used to solve the Euler equations in both nozzle and rotor cascades at hub, mid and tip sections.

The results of these programs solution are used for two purposes.

The first purpose is to obtain an approximate idea about what happens 10 the flow through the turbine stage, while the second purpose is to use the resultant flow properties as an initial guess in the three dimensional solution in order to reduce the number of iterations and computational time required to achieve the steady state solution.

The flow field is divided into two regions, the stator (nozzle) passage region and the rotor passage region, both regions are extended upstream and downstream and there is at least one cell at the upstream of the rotor that must coincide with one cell at the downstream of the stator.

A mesh generation of the flow domain pattern is taken as uniform of (38 X 16 X 20) cells for the stator passage and of (38 X 12 X 20) cells for the rotor passage.

Due to the complexity of the three-dimensional flow in the turbine passages, a checking of the simulating program was made.

The program was tested using a constant area duct with high error in the initial guess.

The convergence was achieved fast and the results were accurate and appropriate with the assumptions taken, namely isentropic and steady flow.

Two types of flow through the turbine stage were studied.

The first flow is without tip clearance between the rotor blade tip and the annular wall whilst the second flow resulted from a specify tip clearance, A comparison of these two flows made it possible to identify the effect of the tip leakage on the flow in the rotor passage.

Throughout the work, the flow field flow properties namely (density, velocity components, pressure and temperature) were calculated, and presented as contours in plain sections (from hub to tip) including the interaction behavior between the stator and rotor.

The results are presented at fleeted positions {from leading edge to trailing edge), including three extensions namely upstream, downstream and the axial gap that is taken as (0 25) of the axial chord of nozzle vane at mid span.

Another comparison between the predicted results and the experimental data shows that the present solutions agree well with those data and the solution is obtained in very economical time.

The CPU time does not exceed (2-4) minutes depending on the effect of the rotor phase location.

The small axial gap taken between the nozzle and rotor passages to the axial turbine in this work shows that the rotor blade passage affects the flow and its properties upstream the passage up to the last (20 %) of the Although the present work solves the in viscid Euler equations it has obtained noticeable rotational and secondary flows upstream the nozzle passage due to its geometry, and through the rotor passage due to the multiple effect of geometry, rotational speed and pressure effect.

It has also been observed that the passage vortex obtained in the rotor passage in the case of no tip clearance was ignored by taking a specific Up clearance of a bout (5 %, i.e.

2, 25 mm) of the blade height.

Finally new stator blade geometry was designed to obtain the same expansion ratio predicted for the whole original turbine stage with less stagnation pressure losses, and that required to design a new rotor blade to complete the stage.

Main Subjects

Mechanical Engineering

Topics

• Fluid dynamics

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-306017