Abstract
The Shongtong Karcham Hydroelectric Project is a 450 MW run-of-river scheme on the Satluj river in Kinnaur district, Himachal Pradesh, developed by Patel Engineering Limited. The water conductor system — comprising headrace tunnels, surge shafts, pressure shafts, and junction structures — is the hydraulic backbone of the project, conveying river water from the intake to the underground powerhouse.
The engineering challenge centred on validating the hydraulic design of the surge shafts and water-conducting junctions under both steady-state and transient conditions. Surge shafts serve as pressure relief mechanisms: when turbines undergo sudden load rejection, the rapid deceleration of flow generates water hammer — a pressure transient that propagates through the conduit system at the speed of sound in water. If the surge shaft geometry is inadequate, peak pressures can exceed the structural capacity of the tunnel lining, and low pressures can induce cavitation — the formation and violent collapse of vapour cavities — causing severe damage to concrete and steel linings.
Prof. Afzal's team conducted three-dimensional CFD simulations of the water conductor system to assess water hammer pressures under load rejection scenarios, quantify head losses through complex junction geometries where multiple conduits converge, and identify zones of cavitation risk at high-velocity sections. The CFD models resolved the full 3D flow field through the surge shaft, penstock junctions, and bifurcation structures, capturing secondary flow patterns, separation zones, and pressure distributions that one-dimensional analysis methods cannot represent.
The simulation results provided Patel Engineering with validated hydraulic design parameters: peak transient pressures at critical sections, head loss coefficients for non-standard junction geometries, and flow velocity maps identifying cavitation-prone zones. These outputs informed design decisions on surge shaft dimensions, junction geometry optimisation, and the specification of pressure-relief devices.
Key Findings
- 3D CFD simulations resolved pressure transients from load rejection scenarios that 1D methods cannot capture.
- Head loss coefficients were quantified for non-standard junction geometries in the water conductor system.
- Cavitation-prone zones were identified at high-velocity sections, informing design modifications.
Methodological Approach
Three-dimensional CFD simulation of the complete water conductor system including surge shafts, penstock junctions, and bifurcation structures. Transient analysis for load rejection water hammer scenarios.
Implications for Hydraulic Practice
Validated hydraulic design parameters for Patel Engineering, enabling informed decisions on surge shaft sizing, junction optimisation, and cavitation mitigation before construction.
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