Turbomachinery: Definition, Types, Core Equations, And Maps

Turbomachinery is the family of rotating machines where a bladed rotor transfers energy to or from a flowing fluid. Turbines extract work from the flow, while compressors, pumps, and fans add work to raise pressure or head. The same core relations also guide scaling, maps, and CFD review checks. (Wikipedia)

If you are working on a turbomachinery problem, you usually need two things at once. You need a clean fundamentals picture, and you also need practical checks that survive a design review.

This page stays fundamentals first, and then it moves into the CFD decisions that most often decide whether results are defensible.

What Is Turbomachinery

Turbomachinery describes machines that transfer energy between a rotor and a continuously flowing fluid. (Wikipedia) You can think of it as one big family because turbines, compressors, fans, and pumps share the same energy transfer logic.

A turbine transfers energy from the fluid to the rotor, but a compressor transfers energy from the rotor to the fluid, and pumps do the same for liquids. (Wikipedia)

How Turbomachinery Is Classified

The first classification is based on energy direction. Turbines are power-producing machines, and compressors, pumps, and fans are power-absorbing machines. (Wikipedia)

The second classification is based on flow path. Axial machines keep flow mostly parallel to the shaft, radial machines turn flow across the radius, and mixed flow machines sit between those two. (Wikipedia)

You will also hear impulse and reaction used, and this matters because it tells you where the pressure drop happens across the stage. (ScienceDirect)

Types And Where Each Fits

Most early selection is not about perfect design. It is about choosing the right machine family for your duty point.

Axial machines fit very high flow rates, and they tend to deliver lower head per stage, so staging is common in axial compressors. Radial machines fit a higher head per stage and compact packaging, which is why centrifugal pumps and many turbocharger compressors are so common. Mixed flow machines balance head and flow when the axial gets too long, and the radial gets too heavy. (Wikipedia)

A Simple Fit Table

How Energy Transfer Really Happens

Energy transfer happens because the rotor changes swirl, so it changes angular momentum. This is why velocity triangles matter in practice, because they make the work transfer visible before you run any CFD. (Massachusetts Institute of Technology)

If the swirl change is small, then the work should also be small, and if your model shows a high-pressure rise with almost no swirl change, you should treat it as a sign check failure. (Massachusetts Institute of Technology)

Core Equations And Symbols

You do not need a wall of math to do good turbomachinery work. You do need a small set of equations that you can use for checks, scaling, and review conversations.

The Euler Turbomachinery Equation

The Euler turbine equation relates specific work to the change in tangential momentum through the blade row. (Massachusetts Institute of Technology)

This equation applies across turbomachines, and it is the core physics link between blades and power transfer. (Massachusetts Institute of Technology)

Symbols Mini Box

Sources:- Massachusetts Institute of Technology

Efficiency That Matches How People Report

For compressors and turbines, isentropic efficiency is the most common reporting choice because it compares real work to ideal work at the same pressure ratio. (GRC NASA)

Polytropic efficiency is also used for compressors because it supports stage comparisons and multistage interpretation, especially when the pressure ratio is high. (ScienceDirect)

Similarity, Specific Speed, And Selection

Similarity is what keeps scaling honest. It is how you move from a duty point to a machine family without guessing, and it is also how you sanity check whether your chosen speed and size are realistic. (ScienceDirect)

Specific speed is a compact way to combine speed, flow, and head, so you can compare machines that are different sizes. In practice, specific speed charts help you choose axial, radial, or mixed flow concepts early, and then you refine the decision using constraints like tip speed, cavitation margin for pumps, and Mach effects for compressors. (ScienceDirect)

The Two Minute Sanity Check That Saves Reviews

Before detailed blading, write down five quick checks. Do it early, because it prevents unrealistic expectations from creeping in later.

• Estimate tip speed and tip Mach, so compressibility risk is visible.

• Estimate a flow coefficient so the incidence risk stays visible.

• Estimate a loading or head coefficient, so the work demand is realistic.

• Check the Reynolds trend, because low Reynolds cuts efficiency. (ScienceDirect)

• Write an expected efficiency band from similar machines. (ScienceDirect)

Compressor Maps And Corrected Terms

A compressor map is a performance chart that shows pressure ratio versus a corrected flow measure, with corrected speed lines and efficiency islands. (Wikipedia)

The left side is the surge or stall boundary, and the right side is the choke boundary, so you use the map to protect operating margin as well as to understand off-design behavior. (Wikipedia)

Corrected Terms Mini Box

Corrected flow and corrected speed exist because you want inlet day conditions removed from the comparison, so the aerodynamic similarity is preserved. (Wikipedia)

Here (\theta) is the temperature ratio to a reference condition, and (\delta) is the pressure ratio to a reference condition. (Wikipedia)

Turbomachinery CFD Review Checks

CFD is powerful for trends and diagnosis, but it is also easy to make a clean-looking mistake. So the safest approach is to treat CFD as a review workflow, not just a solver run.

Start by stating your KPI clearly, like pressure ratio, torque, stage efficiency, or loss split. Then choose the interface model that matches the physics you need, and justify it in plain words.

Rotor Stator Interfaces: Frozen Rotor, Mixing Plane, Sliding Mesh

Frozen rotor passes a steady relative position, so it is often useful as a starting flow field, but it depends on the chosen rotor and stator alignment. (cfd-online.com)

Mixing plane circumferentially averages profiles at the interface, and CFD Online notes that most often a mixing plane simulation gives better results for steady work. (cfd-online.com)

Sliding mesh is the transient approach, and you use it when unsteady interaction changes the KPI, like blade passing loads, tonal noise, or torque ripple. (cfd-online.com)

Mixing Plane Averaging: Area, Mass, And Mixed Out

Ansys Fluent documents three profile averaging methods in the mixing plane model, which are area averaging, mass averaging, and mixed out averaging. (ansyshelp.ansys.com)

Fluent also notes a practical stability workflow. Start with area averaging, and then switch to mass averaging or mixed out after reverse flow dies out, because the latter can face convergence issues when severe reverse flow is present. (ansyshelp.ansys.com)

A Review Safe CFD Checklist

• Confirm rotation direction and work sign from triangles. (Massachusetts Institute of Technology)

• Track torque and pressure ratio until they are flat.

• Show one mesh sensitivity sweep for one KPI.

• State interface choice and why it matches the KPI. (cfd-online.com)

• Report corrected speed and corrected flow for map checks. (Wikipedia)

Real World Applications, With Two Useful Stats

Turbomachinery shows up in power, process, and mobility, and wind turbines are a clear example of scale effects.

DOE reports that in the United States in 2023, the average rated capacity of newly installed wind turbines was 3.4 MW, and the average rotor diameter was 133.8 meters. (The Department of Energy's Energy.gov)

DOE also states that a typical modern land-based wind turbine has blades of over 52 meters, and that GE’s Haliade X offshore wind turbine has blades about 107 meters long. (The Department of Energy's Energy.gov)

References

Turbomachinery definition and scope. (Wikipedia)

Euler turbine equation and angular momentum basis. (Massachusetts Institute of Technology)

Corrected flow and corrected speed forms for maps. (GRC NASA)

Mixing plane averaging methods and stability workflow in Fluent. (ansyshelp.ansys.com)

Mixing plane versus frozen rotor guidance for turbomachinery CFD. (cfd-online.com)

DOE wind turbine growth stats for 2023 installations. (The Department of Energy's Energy.gov)

DOE blade length and Haliade X blade length statement. (The Department of Energy's Energy.gov)

FAQ

What Is Turbomachinery

Turbomachinery is any rotating machine where a rotor exchanges energy with a flowing fluid. It includes turbines, compressors, pumps, and fans, and the shared physics is energy transfer through swirl change and angular momentum. (Wikipedia)

What Do Corrected Flow And Corrected Speed Mean

They are inlet condition corrected variables used on compressor maps. Corrected flow is commonly expressed as (\dot{W}\sqrt{\theta}/\delta) and corrected speed is commonly expressed as (N/\sqrt{\theta}), so different inlet days can be compared fairly. (GRC NASA)

What Is The Most Defendable Rotor Stator Method

Start with a mixing plane for a steady baseline, especially when your KPI is stage performance. Use frozen rotor mainly for a good initial field, and then move to sliding mesh when unsteady interaction changes the KPI. (cfd-online.com)

How Long Are Wind Turbine Blades

DOE states that typical modern land-based blades are over 52 meters, and it also states that GE’s Haliade X offshore blades are about 107 meters long. (The Department of Energy's Energy.gov)

Conclusion

By now, the picture should feel clear and usable. Turbomachinery is not just a definition, but a set of machine families with shared physics. You saw the types, the work transfer logic, and the few equations that anchor your intuition. Along with that, you now have the review safe CFD checks that stop results from drifting. We also covered tip clearance losses and Conjugate heat transfer, because those are where real projects fail quietly. If you want to build this skill faster, our CFD course walks you through the same workflow with templates and real turbomachinery cases.