Design of a ti-6al-4v heat exchanger using dimensional analysis for use in aeronautical turboshaft engines

Abstract

While post-compression intercooling is a commonly utilised method to increase or optimise the performance of traditional turbocharged internal combustion engine layouts, there exists a potential in installing similar modifications in aeronautical turboshaft engines. The rise of additive manufacturing (AM) techniques now offers the potential for lighter and more compact heat exchangers to be designed and manufactured. To this end, a theoretical intercooler system was designed to cool the charge air supplied by the compressor stages of a turboshaft engine to increase the performance of the engine. With cooler air supplied by the compressor stage theoretically having the capacity to reduce the amount of work required by the compressor stages as well as benefiting the containment effects inside the combustor unit. A benchmark engine was selected and characterised by a simple Brayton gas cycle, which indicated that there was an overall temperature increase of 234.710 °C across the compression process due to the heat of compression. Using the Kays and London method for a full-sized multi-pass heat exchanger, a heat exchanger was successfully designed, which would fulfil all the requirements to evaluate the feasibility of the concept. A test piece was then extracted from the design and successfully manufactured at half scale using Ti-6Al-4V titanium alloy. The theoretical intercooler unit consisting of two full-size multi-flow heat exchangers was able to cool air supplied at a mass flow rate of 1.638 kg/s by an estimated 28.542 °C. Dynamic similarity constraints obtained via dimensional analysis techniques were then successfully applied to determine the experimental testing conditions required to verify the full-scale design. An experimental test bench was designed and fabricated to simulate the required testing conditions to attain dynamic similarity. A series of six tests, consisting of eight readings each, were performed over a time span of two weeks, where exact measurements were taken of the heat transfer across the test piece heat exchanger. The results recorded from the experimental testing phase of the project indicated that the process whereby a portion was extracted from a heat exchanger and verified using dynamic similarity was not only viable but yielded much better results than expected. The experimental results showed a substantial correspondence to the theoretically expected calculations. The outcome of this research aims to clarify the suitability of a heat exchanger manufactured using AM techniques for use in aeronautical turboshaft engines.