A Study on the Flow Characteristics and Primary Energy Conversion in a Direct

Abstract

Due to recent developments such as increasing price of fossil fuels and environmental issues associated with fossil fuels, there is a need to find alternative energy supplies. Wave energy offers such a solution. Wave energy is the most consistent of all the intermittent renewable energy sources. In addition to this, very large energy fluxes occur in the ocean waves and by using appropriate wave energy converters the energy can be harnessed. The present study looks at utilizing a direct drive turbine of cross flow type to extract energy from the incoming waves. Currently, the model does not include the runner. The purpose of the present study is stated below:

◆ Successfully simulating waves in a numerical wave tank (NWT) using the commercial code of ANSYS CFX.

◆ Study flow characteristics in the front guide nozzle, augmentation channel and the rear chamber of the base model. Obtain water power and primary energy conversion for the base model.

◆ Conduct simulation of the entire model at different wave period to obtain the best wave condition to achieve maximum water power.

◆ Maximize the primary energy conversion of the base model by making modifications to front guide nozzle, augmentation channel and the rear chamber.

After obtaining the best designs of all the individual components, that is the front guide nozzle, augmentation channel and the rear chamber

a final model was obtained and its performance with respect to the base mode was investigated. The water power and the primary energy conversion for the base model was 29.9W and 0.5 respectively. On the other hand, for the final model the water power and the primary energy conversion were 40.2W and 0.67 respectively. This represents an increase of 34% in primary energy conversion when compared to the base model.

In addition to this, the overall optimization yields better flow characteristics in the front guide nozzle, the augmentation channel and in the rear chamber of the final model. Average velocity in the front guide nozzle of the final model is 16% higher than the base model and also an increase of 10% is recorded for the peripheral velocity. This improvement thus leads to higher energy conversion.