ENGINEERING – PUMP & TURBINE CALCULATOR
Turbine Efficiency Hill Chart
A precise tool.
What is the Turbine Efficiency Hill Chart & How does it work?
The Hill chart is a graphical representation that relates turbine efficiency to offβdesign operating points. It is built from a baseline design conditionβtypically the point of maximum efficiencyβand shows how efficiency degrades as the flow coefficient ((phi)) and pressure ratio ((PR)) move away from their design values. Engineers use the chart to predict performance across a range of loads without running a full CFD simulation.
Offβdesign efficiency can be approximated by scaling the design efficiency with the ratios of the current operating parameters to their design counterparts. The underlying assumption is that the turbineβs aerodynamic losses vary proportionally with changes in flow and pressure, which holds true for many axialβflow and radialβflow machines operating within their linear region.
By plotting the calculated efficiencies on the Hill chart, designers can quickly identify safe operating envelopes, evaluate the impact of speed changes, and size control systems. The chart also aids in troubleshooting, as deviations from the predicted curve often point to fouling, wear, or control issues.
\eta = \eta_{design}\,\frac{\phi}{\phi_{design}}\,\frac{PR}{PR_{design}}\,\frac{N}{N_{design}}
\eta = turbine efficiency at offβdesign, \phi = flow coefficient, PR = pressure ratio, N = rotational speed
Parameters
Result
β
Frequently Asked Questions
What is a Turbine Efficiency Hill Chart?
A graphical representation showing how turbine efficiency changes with flow coefficient and pressure ratio from design values.
How do engineers use the Hill chart?
Engineers use it to predict turbine performance at off-design operating points without running full CFD simulations.
What does the baseline design condition represent on the Hill chart?
The baseline design condition represents the point of maximum efficiency, typically used as a reference for scaling other conditions.
How is off-design efficiency approximated using the Hill chart?
Off-design efficiency is approximated by scaling the design efficiency based on changes in flow coefficient and pressure ratio.
What are the main variables considered in the Hill chart?
The main variables are flow coefficient (Ο) and pressure ratio (PR), which determine how efficiency degrades from design conditions.
Why is the Hill chart useful for turbine performance analysis?
It allows engineers to quickly assess turbine performance across a range of operating conditions without extensive computational resources.
Can the Hill chart be used for all types of turbines?
While primarily used for gas turbines, similar concepts apply to other types of turbines with appropriate modifications.
Results are for informational purposes only and do not constitute professional advice.