"The effects of inlet swirling flow on the pressure recovery of a low h" by Sok Piseth

The effects of inlet swirling flow on the pressure recovery of a low head turbine draft tube model at different reynolds numbers using ANSYS fluent

Date of Publication

7-2016

Document Type

Master's Thesis

Degree Name

Master of Science in Mechanical Engineering

Subject Categories

Mechanical Engineering

College

Gokongwei College of Engineering

Department/Unit

Mechanical Engineering

Thesis Adviser

Gerardo L. Augusto
Aristotle T. Ubando, co-adviser

Defense Panel Chair

Archie B. Maglaya

Defense Panel Member

Laurence A. Gan Lim
Neil S. Lopez

Abstract/Summary

A draft tube is one of the hydraulic turbine components that is used to reduce the head loss thereby increasing the net head available to the turbine runner. It is used in converting kinetic energy into static pressure energy resulting to pressure recovery. In practice, the available energy at the site and energy demand usage varied which has led to the operation of hydraulic turbine either at part load or full load condition. Such load conditions should be operated at its best efficiency point by varying the swirling flows at diffuser inlet that might improve the draft tube performance. This study shows the significance of swirling inlet flow in an axial flow turbine draft tube model at different rotational rates and Reynolds numbers. The configuration of turbine draft tube model has a cross-section changing from annular to rectangular. Forced vortex type of tangential velocities were introduced at diffuser inlet with different Reynolds numbers and rotational rates. In this study, air was used as a working fluid instead of water due to its incompressible condition when the change in fluid density as a result of pressure variations is negligible. Numerical software such as ANSY Fluent with RNG π‘˜βˆ’πœ€ turbulent model was used in performing the simulations. Two different cases of studies were considered. The first study involves performing simulations of swirling inlet flow in a three-dimensional diffuser at a Reynolds number of 40,000 with different rotational rates from N = 0.0 to 0.504 and considering the actual pressure drops obtained from previous experiments. Case 2 is hypothetical studies where simulations were performed at different Reynolds numbers of 40,000, 50,000, and 60,000 with strength of swirls changing from 0 to 1 and considering the diffuser outlet was exposed to atmospheric pressure condition. Dimensionless axial and tangential velocity profiles at diffuser inlet and coefficient of performance were obtained using ANSYS Fluent and discussed in this paper. The numerical results of case 1 were also compared with the previous experimental studies conducted by Augusto et al., 1997.The numerical simulations were successfully modelled with the errors ranging from 0.8% to 1.5%. The results showed that there was in good agreement between the numerical and previous experimental results. In case 1, the numerical results indicated that the improvement of pressure recovery was found at moderate swirl, whereas the deterioration took place at low and high swirl due to stall regime developments in the diffuser. On the other hand, in case 2, the numerical results confirmed that when the Reynolds number increased, the deteriorated rotational rate decreased (the deteriorated rotational rate is the rotational rate where the diffuser performance becomes to deteriorate.) Further results of case 2 showed the diffuser performance reached the maximum value at the Reynolds number of 50,000 and the rotational rate of 0.840. The regression analysis on numerical data allowed to generate equations with the acceptable coefficient of determination so that they can be accurately used to represent the data and predict the diffuser performance without further simulations.

Abstract Format

html

Language

English

Format

Electronic

Accession Number

CDTG006883

Shelf Location

Archives, The Learning Common's, 12F Henry Sy Sr. Hall

Physical Description

1 computer optical disc; 4 3/4 in.

Keywords

Hydraulic turbines

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Embargo Period

10-17-2024

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