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INSPiRE Report Summary

Project ID: 717228
Funded under: H2020-EU.

Periodic Reporting for period 1 - INSPiRE (Industrialisation of Jet Noise Prediction Methods)

Reporting period: 2016-07-01 to 2017-12-31

Summary of the context and overall objectives of the project

Jet noise is a significant component of overall aircraft noise and consequentially has a detrimental societal impact as air transport continues to grow. Although pure jet noise has successfully been reduced by the trend towards increasing engine diameters, the same trend is leading to a strong increase in the interaction noise caused by the jet's proximity to the wing and flap. The development of countermeasures is currently held back by a lack of understanding of the interaction mechanism, which could be delivered by high-fidelity turbulence-resolving simulations. The industrial exploitation of such simulation technologies is however prevented by their high computational expense and the lack of sufficiently robust simulation processes for such complex configurations.

The INSPiRE project contributes to the industrialisation of jet noise prediction technology, by driving forward the development of scale-resolving methods for the prediction of installed jet aeroacoustics. The focus is on a family of turbulence-resolving approaches known as Detached-Eddy Simulation (DES), in which the jet plume region is resolved whereas the attached boundary layers captured more efficiently with lower-order models. The propagation of acoustic signals to far-field observers is accomplished in a hybrid approach for maximum efficiency.

The specific objectives of the INSPiRE project are:

- To enable the simulation of higher frequencies at minimal additional computational overhead through the extension of an innovative meshing strategy
- To improve the flexibility and reliability of far-field noise integration by pioneering the automatic detection of optimal FWH data surface placement
- To define and validate procedures to automatically demarcate the initial transient and statistically-steady states of the solution and to define statistical error bars on flow and far-field noise quantities using innovative in-house algorithms
- To achieve at least a 20% reduction of computational effort for jet noise simulations via accelerated initialisation techniques
- To validate the enhanced DES/FWH process chain against a database of existing measurements including complex jet-flap configurations and low noise 3D nozzle design
- To establish, document and verify best practice guidelines corresponding to the newly-developed methodologies
- To ensure direct exploitation of the developed technologies by conducting validation simulations and implementing applicable improved methods in an industrial CFD solver

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Technical work in the first reporting period has been concentrated on the development of the improved methodologies, as well as their validation for a simplified single-stream jet case. The work has been organised into four main tasks:

1. "Hybrid structured/unstructured meshing strategy":
An enhanced hybrid meshing strategy was applied to achieve a factor four increase in the azimuthal resolution near the nozzle with only 30% increase in CPU cost per iteration compared to a structured datum grid. Clear improvement in the mean flow and far-field acoustic prediction was achieved, with spectra at the peak observer angle predicted to within 1dB up to a Strouhal number of 3. Importantly, no spurious noise was identified despite the increased levels of unstructured meshing.

2. "Efficient and flexible far-field noise integration":
A novel sensor function was evaluated in a precursor simulation to automatically determine the optimal FWH data surfaces location. The approach is expected to make a significant contribution to industrialisation, since it maximises computational efficiency whilst minimising user burden.

3. "Statistical evaluation of simulation progress":
A procedure has been developed and validated for the automatic statistical evaluation of DES/FWH simulations of jet noise. Novel statistical algorithms were found to give reliable detection of the "initial transient" phase of the simulation. The method enables the optimisation of computational resources through minimisation of wastage typically arising from over-estimation of the initial transient. Furthermore, the potential for automatic processing of far-field statistics reduces user burden. The definition of statistical error bars on far-field directivity plots is an important additional benefit, e.g. to discriminate true noise differences from statistical error when judging competing designs.

4. "Initial transient acceleration techniques":
Two separate methodologies were investigated to reduce computational wastage in the initial transient computation. A more efficient simulation process involving lower-fidelity computation of the initial transient combined with optimised computational settings for the productive statistical portion resulted in a factor 7.6 reduction of computational expense compared to previous best practice settings. This greatly exceeds the project objective of a 20% efficiency gain.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

For each of the four sub-topics, the state of the art before the INSPiRE project ("before") can be compared to the progress achieved beyond the state of the art due to the INSPiRE project ("after") as follows:

1. Hybrid structured/unstructured meshing:
- BEFORE: In-house methods pioneered, including techniques for smooth structured/unstructured interfacing
- AFTER: Extension of meshing strategy to include local azimuthal refinement in early shear layer(s)

2. Efficient & flexible far-field noise integration:
- BEFORE: Parallel FWH implementation and validated FWH surface data reduction approach for fast turnaround time; Validated method to (manually) define data surface locations irrespective of mesh
- AFTER: Sensor to automatically detect optimal FWH placement for arbitrarily complex cases

3. Statistical evaluation of simulation progress:
- BEFORE: In-house methods for automatic initial transient detection and statistical error quantification of input monitor signals; Efficient implementation of algorithms in software tool meancalc
- AFTER: Validation of meancalc specifically for jet flows and derivation of associated best practice (monitor signals and quantities to evaluate)

4. Initial transient acceleration techniques:
- BEFORE: Reports in the Literature that lower-fidelity transient simulation increases efficiency – not yet attempted with current industrial process chain
- AFTER: Validation of optimal low-fidelity initialisation approach in industrial process, achieving factor 7.6 reduction in overall computational expense

Currently these approaches have been validated for a simple single-stream jet case. In the second half of the project, the approaches will be evaluated for complex installed coaxial jet/wing interaction cases with a variety of flight conditions and flap settings.

By making a tangible contribution to the industrialisation of high-fidelity jet noise prediction methods, the INSPiRE project therefore delivers a significant contribution to the challenging goals set by the renewed ACARE Strategic Research and Innovation Agenda, namely a 65% reduction in perceived noise by 2050 compared to 2000 levels.

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