Read operating point, surge line, and risk gauge together to see how lower flow or higher pressure ratio consumes margin.
Parameters
Corrected flow
kg/s
Corrected mass flow on the compressor map.
Surge-line flow
kg/s
Flow at the surge line for the same speed.
Pressure ratio
-
Outlet total pressure divided by inlet total pressure.
Corrected speed
%
Speed line relative to design speed.
Real-time surge map animation
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Operating PR
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Corrected flow [kg/s]
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Surge margin [%]
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State
Surge lineConstant-speed linesOperating point
Surge margin $SM=100(\dot m-\dot m_{surge})/\dot m$ is evaluated at the operating point. As the point nears the surge line, the point and line turn red to signal the unsafe side.
Results
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Surge margin
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Pressure ratio
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Surge risk
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Speed line
Compressor operating map
Flow margin curve
Surge risk
Model and equations
$$SM=100\frac{\dot m-\dot m_{surge}}{\dot m}$$
Surge margin is a first-pass measure of distance from the operating point to the surge line. Real machines also require inlet corrections, guide-vane effects, bleed, and transient response.
How to read it
The map shows risk increasing as the operating point approaches the surge line.
The margin plot shows how flow reduction consumes margin.
The gauge gives a quick safe, caution, or danger reading.
Learn Compressor Surge Margin Map by dialogue
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When reading Compressor Surge Margin Map, where should I look first? Moving Corrected flow changes both the plots and the result cards.
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Start with Surge margin, but do not treat the number as the whole answer. Use Compressor operating map to confirm the assumed state, then read Flow margin curve for the distribution or trend. The map shows risk increasing as the operating point approaches the surge line.
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I can see why Corrected flow changes Surge margin. How should I judge the influence of Surge-line flow?
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Move Surge-line flow in small steps and watch Pressure ratio. That reveals which term is controlling the result. Surge margin is a first-pass measure of distance from the operating point to the surge line. Real machines also require inlet corrections, guide-vane effects, bleed, and transient response. A single operating point is not enough; sweep the realistic scatter range.
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What is Surge risk for? It feels like the ordinary curve already tells the story.
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Surge risk is for finding boundaries where the condition becomes risky or margin collapses quickly. The margin plot shows how flow reduction consumes margin. In Compressor operating-range reviews, the important question is often what happens after a small change, not only the nominal value.
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So if Surge margin is within the target, can I accept the condition?
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Treat this as a first-pass review. It helps with Checking margin after control or bleed changes and Screening risky conditions before testing, but final decisions still need standards, measured data, detailed analysis, and vendor limits. The gauge gives a quick safe, caution, or danger reading.
Practical use
Compressor operating-range reviews.
Checking margin after control or bleed changes.
Screening risky conditions before testing.
FAQ
Start with Surge margin and Pressure ratio. Then use Compressor operating map to confirm the assumed state and Flow margin curve to read distribution or bias. The map shows risk increasing as the operating point approaches the surge line
Move Corrected flow alone, then move Surge-line flow by a comparable amount and compare the change in Surge margin. Surge risk shows combinations where margin or performance changes quickly.
Use it for Compressor operating-range reviews. Instead of trusting a single point, widen the input range and check whether Surge margin keeps enough margin before moving to detailed analysis.
Surge margin is a first-pass measure of distance from the operating point to the surge line. Real machines also require inlet corrections, guide-vane effects, bleed, and transient response. Final decisions still require standards, measured data, detailed analysis, and vendor limits.
How to Use
Enter corrected mass flow rate (kg/s) in the flow field; typical range 15–85 kg/s for industrial centrifugal compressors.
Set pressure ratio (PR) between 1.5–4.2 using the pr slider; this defines the thermodynamic operating point on the compressor map.
Adjust compressor speed (rpm) between 8,000–15,000 to trace speed lines; the simulator plots your position relative to the surge line and calculates margin percentage.
A 10-stage axial compressor operating at design speed 12,000 rpm ingests 42 kg/s corrected flow at pressure ratio 2.8. The surge line at this speed intersects 2.8 PR at 38 kg/s. Calculated surge margin = ((42–38)/38)×100 = 10.5%, placing the engine in yellow-line (caution) territory. Reducing PR to 2.4 shifts operating point to 48 kg/s, increasing margin to 26%—safe zone. Increasing speed to 13,200 rpm moves surge line left to 36 kg/s at 2.8 PR, reducing margin to 17%.
Practical Notes
Surge lines slope leftward on compressor maps; margin shrinks rapidly near peak pressure ratio—avoid operating above 90% of design PR during transients.
For turbocharged diesel engines, maintain minimum 20% surge margin during acceleration to prevent compressor rotating stall and turbo lag spike.
Speed lines are nearly vertical; a 5% rpm reduction shifts your operating point ~8–12% rightward in flow, significantly recovering margin without load penalty.