Project SECRET is entering its third year and the whole team is excited about the next phase. To review the hard work and recap the previous year, we organised a whole-day event on the 27th of September in Howden factory in Glasgow. City team was able to meet with Howden members in person and discuss the progress we made in the last year, as well as ideas and plans for the future period. Our Royal Academy of Engineering Mentor Prof Robert Wood also joined us and gave the team some useful advice. Howden team organised a tour around the factory, where we were able to see the newest achievements and products.

The annual review meeting was held in presence of Royal Academy of Engineering Programme Office Joel Chen, Prof Alfredo Pinelly, Associate Dean for Research at School of Science and Technology at City. Prof Ahmed Kovacevic presented the progress and achievements from Year 2, and Douglas Latta spoke about the positive effects the project has on the overall Howden atmosphere and public relations. Prof Wood gave his feedback on all aspects of the project and gave helpful suggestions about future steps.

Douglas Latta, HOWDEN said:

Phase 2 of Project SECRET has provided the team with a clear roadmap of how we can develop the initial research findings of leakage flows and heat transfer effects in oil free compressors. The collaboration between the Howden and City University teams has grown into a fully formed relationship with the relative skills and experience being freely shared and for me that is the number 1 success of this phase which will stand us in good stead for phase 3. We now want to turn the initial findings into more practical outcomes using the test rig which has been constructed. It becomes more real for us at Howden when we see the theory outcomes being validated in a test setting. Even though we will only be half way through Project SECRET, from there I see us quickly transferring this knowledge quickly into our core compressor design and test methodology.


3D CFD models that are currently in practise were extended to include heat transfer to and from the metal components of the compressors


In phase 2 of the project, 3D CFD models that are currently in practise were extended to include heat transfer to and from the metal components of the compressors. Numerical issues such as heat transfer time scale disparity and computational boundary conditions surfaced and have been identified to be tackled as the research progresses. External heat transfer boundary conditions such as specified HTC or modelling an exterior domain were investigated. These developments have now enabled us to get into the details of flow physics, study interaction of the metal and fluid during compression and validate the models using measured data.

In the same time, Particle image velocimetry measurements were carried out in dynamic condition and static condition of the machine to measure clearance flows. PIV data was post processed and velocity vector fields were generated. This data reveled interesting flow structures such as boundary layer, vortexes, and velocity fluctuations in clearance gap. These results are now being utilized to improve tip surface design to reduce leakage losses.

It was concluded that the project is on track and the commitment of the both Howden and City team was praised. It was also noted that the project connects different stakeholders and made some new connections between research groups at City. The promotion of the project was marked as excellent, and all members felt its impact of it.


Particle image velocimetry measurements were carried out in dynamic condition

Highlights of the Year 2:

  • 2 journal papers were published
  • 8 conference papers presented at two major compressor conferences
  • award for the best student paper at Purdue conference won for the paper related to findings from Project SECRET
  • attended 8 relevant events where we promoted the project
  • PIV testing of leakage flows during running conditions was completed and data has been processed
  • model for conjugate heat transfer in leakage gaps was developed
  • integration of DDA in CITY test rigs was completed
  • concepts for improving the efficiency and reliability of oil-free twin screw compressors have been developed and assessed
  • design and manufacturing of the test rig are progressing well
  • CERES industrial consortium was established around the Centre for Compressor Technology at City
  • one patent application was made

Our team is about to grow in October when a new PhD student joins City, University of London. We are now making concepts which will be implemented in the prototype in the 3rd year of study as the basis for commercialisation win Howden. We are confident that in Year 3 we will manage to keep up with the planned activities to evaluate prototypes with new concepts for improving the reliability and efficiency of rotating compression machines. Testing of these concepts will be completed in Year 3 in order to determine technologies which will be implemented in commercial machines later in the project.

Prof Ahmed Kovacevic, CITY concluded:

We are extremely grateful to the RAEng for giving us the opportunity to work on this challenging task. In phase 2 we completed experimental investigation of leakage flows and developed methods for numerical simulation of Conjugate heat transfer in leakage flows. We have installed the test rig for prototype development and verification and performed the initial test on laboratory prototype. Using a rigorous design process we have defined four areas where the new concepts are being developed. As a part of this process the team came to an idea for discharge valves in oil free screw compressors and submitted patent application for this solution.


In the short term Howden will implement some of these concepts like regulation of clearances and control mechanisms in their oil free screw compressors which will make quick wins of new projects and increase sales. In the long term, new machines will be designed with superior performance and increased reliability which will ultimately result with the shift in the market in the use of oil free machines. We believe that current 17% market share of oil free screw machines will increase at least 10% in the next 5-10 years leading to reduced carbon footprint and more reliable operation.