Scale: N/A

A major expansion of the existing Waste Water Treatments Works in Santiago, Chile was proposed.  As part of the expansion, eight grit channels are proposed upstream of a multi-level flow distribution chamber.  A distribution system is also proposed upstream of the grit channels to provided acceptable distribution of flows to each of the channels.

The purpose of the CFD analysis was to establish the operating characteristics of each option and to develop the design, where considered necessary, to achieve a satisfactory distribution of flow through each of the grit channels.  The study considered the distribution of flow through the grit channels when operating at 11.0 m3/s and 6.6 m3/s respectivily.

The grit channels should operate in an environment where reasonable flow distribution is maintained across all operational channels.

A statistical analysis of flow through each of the grit channels observed a maximum deviation from the mean flow of +5.61%.  This was considered to represent  acceptable flow distribution across the grit channel network.

A minor deterioration in the distribution of flow across the network was observed due the elimination of a single grit channel (for maintenance purposes), and during an increase in the capacity of the network (6.6 m3/s with 5 channels to 11 m3/s with 7 channels).  However, any deterioration in the distribution of flow across the network was not considered significant.

Streakline plots across the network also gave a visual illustration of good flow distribution across the grit channels.  Velocity plots across the network during all cases indicated even distribution of flow within the distribution channels, screen channels and grit channels. 

Analysis within each grit channel illustrated that although the jet of incoming flow was  concentrated toward the centre of the channel within the first 7.0 m of the tank, within 10.0 m of entering each channel the velocity of flow became evenly distributed across the width of the tank.  This indicated that the grit channels were operating efficiently, with no significant jetting within the tanks.