ashfordeOU Compressor Map (propulsion/axial-compressor/compressor-map)
Use when the task is an axial compressor operating map: map axes, surge and operating lines, corrected flow and speed, surge margin, operating-line clearance, and the surge-risk verdict for a running point.
Domain quick reference
- Map axes: total pressure ratio (dimensionless) on the vertical axis, corrected mass flow (kg/s) on the horizontal axis. Each iso-speed line is a curve in this plane.
- Stable region boundaries: the surge line on the left (locus of peak-pressure-ratio points, one per speed) and the choke line on the right (blocked flow, flow independent of pressure ratio).
- The operating line is the design locus of running points across speeds; it sits below the surge line with a clearance.
- Standard-day correction, T_ref = 288.15 K, P_ref = 101325 Pa: theta = Tt/T_ref, delta = Pt/P_ref, both dimensionless.
- Corrected mass flow m_corr = m_actual*sqrt(theta)/delta in kg/s; corrected rotor speed N_corr = N_actual/sqrt(theta) in rpm.
- Flow-basis surge margin (percent), at the same corrected speed: SM = (q_operating - q_surge)/q_operating*100. The surge point is at lower flow than the running point, so positive SM is the safe side.
- Operating-line clearance (percent), at the same corrected flow: CL = (pr_surge - pr_operating)/pr_operating*100. Positive means the operating line is below the surge line.
- Surge-risk verdict at a corrected flow: "on-map" when the fractional gap to the surge line exceeds the threshold (default 5%), "approaching-surge" inside it, "on-surge-line" at or above surge pressure ratio.
- Acceleration path: a transient moves the point up a speed line toward higher pressure ratio and speed; the transient margin is smaller than the steady-state margin because the point must stay below the surge line throughout.
- Units: flows in kg/s, speeds in rpm, temperatures in K, pressures in Pa, ratios and verdicts dimensionless.
Workflow
- Identify the map point: corrected_speed and corrected_flow from the measured speed and mass flow with the theta/delta corrections.
- Read the surge-line pressure ratio and flow at that point from the map (surge_pr, q_surge).
- Compute the flow-basis margin with surge_margin_flow.
- Compute the pressure-ratio clearance with operating_line_clearance.
- Classify the point with map_verdict.
- Assess the acceleration path: the transient must keep the point below the surge line; a verdict of approaching-surge or on-surge-line rejects or trims the schedule.
- Report margin, clearance, and verdict; gate the operability review on the clearance staying positive.
Pitfalls
- Mixing corrected and raw quantities: the map is drawn in corrected flow and corrected speed, so raw values must be theta/delta corrected before any point lookup.
- Confusing the two margins: flow-basis margin is read at constant corrected speed, pressure-ratio clearance at constant corrected flow; mixing the reading directions mixes the numbers.
- Forgetting that theta and delta are dimensionless ratios, not temperatures or pressures: pass Tt/288.15 and Pt/101325, not Tt and Pt themselves.
- Zero or negative inputs (flow, speed, theta, delta, surge pressure ratio at or below unity): the functions raise ValueError rather than divide by zero; do not catch and continue.
- Treating the default 5% threshold as a requirement: it is a default; the engine program sets the transient surge margin requirement.
- A negative margin or clearance is not a rounding error: it means the operating point is on the unstable side of the surge line.
Behavior contract (gate 3)
The map logic is exercised by the gate 3 contract test: scripts/test_compressor_map.py against scripts/compressor_map_logic.py (stdlib unittest, offline). Run: python3 scripts/test_compressor_map.py
Compliance
- Standards referenced, not reproduced: FAR-33 is US government work (public domain) and covers engine type certification, not map analysis methods; the map conventions and correction relations are common turbomachinery methodology, summary-only per standards-map.yaml.
- compliance: STANDARDS-REF, gated: false.