Engines and Power Cycles, Turbomachinery and Secondary Flows
System-level analysis of jet and rocket engines, power generation cycles, heat pumps and refrigeration loops, etc. can be made using performance map-based descriptions of single- or multi-stage pumps, fans, turbines, and compressors. These elements predict flows and pressure drops, using either directly input maps (single curves or multiple curves per shaft speed) of flow versus pressure drop, or maps specified using equivalent states, reference states, head and flow coefficients, etc. Isentropic efficiencies may be specified, enabling the code to predict shaft power and hydraulic torque. Tables of flow and efficiency relationships are normally input, but options exist for parametric inputs, functional (algorithmic) descriptions, as well as links to turbomachine design software.
- Pumps: Reference speeds or flow/head coefficients (to exploit pump similarity laws), cavitation detection and modeling (based on either NPSH or Nss) , viscosity corrections, and two-phase flow degradations. Nonmonotonic curves (with positively sloped regions) are permitted.
- Turbines: Equivalent conditions, including equivalent speed options available. Handling of choking and truncated tables, and two-phase outlet states. Total-total, total-static, and other inlet/outlet state options. Efficiency may optionally be a function of U/C: the blade tip velocity to isentropic spouting velocity (or fluid jet velocity) ratio. Power (or equivalent power) may be specified instead of efficiency.
- Compressors (Variable displacement): Equivalent conditions, including equivalent speed options available. Handling of choking and surge regimes. Total-total, total-static, and other inlet/outlet state options. Power (or equivalent power) may be specified instead of efficiency. Nonmonotonic curves (with positively sloped regions) are permitted.
- Compressors (Positive displacement): Flow specified via volumetric efficiency (versus speed and/or pressure ratio) and displacement volume. Power may be specified instead of isentropic efficiency.
Engines and Cycles
Design and analysis of engine or power cycles can include single- or two-phase flow components such as boilers, condensers, regenerative heat exchangers, control valves, etc. in either steady or unsteady analyses. For systems with interconnected turbomachines (e.g., turbochargers, turbopumps, turbojets, etc.), shaft speeds can be predicted to balance torques in steady-states, or shaft/gear mechanical speeds can be solved in transients concurrent with the cycle thermohydraulics.
Extensive options exist for modeling passages within rotating machinery, including between rotating and stationary parts. Analysis of secondary coolant, leakage, or lubricating flows can exploit built-in correlations or user-supplied correlations for friction, heat transfer, and torque.
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