This case study with Lufthansa shows Flownex effectively models secondary flow in a CFM56-5C turbomachine with results within 10% of detailed 3-D CFD, but in seconds instead of hours. Flownex saves engineering time and costs by enabling quick, accurate 1-D CFD simulations for turbomachinery design and sensitivity studies.
CHALLENGE
Modelling the flow in turbomachinery is often seen as a task that can only be performed by detailed 3-D CFD analysis, requiring expensive hardware, advanced modelling techniques, and experienced CFD engineers. Furthermore, time scales for detailed turbomachinery 3-D CFD analysis can become prolonged due to the complex geometry and a fine mesh required to get a sufficiently accurate solution representative of the actual physics.
BENEFITS
Various flow paths of turbomachinery can be accurately modelled using a 1-D CFD approach as opposed to 3-D CFD. Furthermore, due to the influx of new turbomachinery technology, new designs need to be assessed in the CFD environment and doing this in a 1-D environment saves engineering time and money
SOLUTION
Lufthansa investigated the possibility of using Flownex SE in the secondary flow analysis of a CFM56-5C turbomachine. Results were obtained from a detailed 3-D CFD analysis, and Flownex showed good agreement with the 3-D CFD results to within 10%. Solving time of the Flownex models was in a matter of seconds, whereas the CFD models were in the order of hours.
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INTRODUCTION
Using a 1-D modelling approach to secondary flow analysis for turbomachinery saves engineering time and money. A study was recently done by Lufthansa and Flownex SE in order to compare detailed 3-D CFD results with Flownex on the secondary cooling flow through the Low-Pressure Turbine (LPT) first stage stator vane of the CFM56-5C turbomachine
METHODOLOGY
A Flownex SE model, shown in Figure 2, was set up to model the secondary cooling airflow path from the 1st LPT pipe position up to the respective cavities where flow leaves the vane assembly.
The model’s boundary values represented the inlet static temperature and pressure, as well as the cavity static pressures supplied from the 3-D CFD analysis results.
The Flownex SE model shows only 1 flow path, but the applicable “Number in parallel” values were specified in order to model the flow through all 96 vanes. Composite heat transfer elements were used to model the heat transfer from the vane surface to the fluid, with the material assumed to be a coated metal having a specified conductivity.
The mass flow resulting from the outer pressure difference and geometric flow resistance was used for comparative purposes, as well as the static pressures and temperature results calculated at the other network positions obtained from Lufthansa.
RESULTS
By using boundary conditions obtained from 3-D CFD results, Flownex SE calculated a mass flow rate of 1.84 kg/s. This correlates well with the expected mass flow rate of 2 kg/s from the Lufthansa estimation. The same went for the pressure drop results.
CONCLUSION
Simulation time for the Flownex SE model to solve was a matter of seconds, which provided quick results for comparison to the 3-D CFD results. Results obtained from Flownex SE proved to provide a high degree of accuracy when compared to expected results and 3-D CFD results.
Flownex SE is now being used by Lufthansa as part of their turbomachinery design software suite. This enables them to quickly do various simulation runs for varying sensitivity studies and evaluate the performance impact on the engine with consideration of wear and tear, saving them valuable engineering time and money.