# Entropy Production Analysis and Fluid–Structure Refinement of a Stepless Stratified Intake

## TL;DR

This study uses entropy production to analyze energy loss in a stepless stratified intake system and suggests design improvements to reduce inefficiencies.

## Contribution

The paper introduces entropy production as a diagnostic tool for analyzing energy dissipation in stepless stratified intakes and proposes effective geometric modifications.

## Key findings

- Turbulent entropy production accounts for over 98% of total dissipation in the intake system.
- Flow turning at gate leaves and wake development around braces are the main sources of energy loss.
- A combined brace-alignment and edge-rounding design reduces dissipation hotspots and improves discharge sharing.

## Abstract

Thermal stratification in deep reservoirs can cause ecologically problematic cold-water releases, and many existing selective-withdrawal phenomena rely on a limited set of fixed intake levels, which constrains their ability to follow seasonal shifts in the thermocline. Stepless stratified intakes with continuously adjustable flap gates offer quasi-continuous control of withdrawal depth, but their multi-gate, multi-brace layouts generate complex internal hydraulics whose energy-loss mechanisms are not well captured by conventional head-loss and resistance-coefficient metrics. In this study, physical-model measurements are combined with a validated three-dimensional numerical model, and entropy-production theory is used as a diagnostic to resolve where and by which mechanisms mechanical energy is irreversibly degraded inside a single-unit stepless stratified intake. The analysis shows that turbulent entropy production accounts for more than 98% of total dissipation, concentrated mainly in the flow channel and gate shaft, while the reservoir and outlet pipe contribute only weakly. Local entropy-production-rate fields indicate that dominant irreversibilities are associated with flow turning at the active gate leaves and with separation and wake development around horizontal and vertical braces, which generate low-velocity bands across gate levels and a low-velocity corridor in the shaft. Five geometric modification schemes targeting gate-entrance shaping and brace layout are evaluated; a combined brace-alignment and edge-rounding configuration most effectively weakens dissipation hotspots, improves discharge sharing among gate levels and reduces total entropy production. These findings show that entropy-based diagnostics can complement traditional hydraulic indicators and provide effective guidance for the design and refinement of stepless stratified intake structures.