Evolution from ‘Tabs’ to ‘Chevron Technology’ - A Review

‘Chevrons’, a sawtooth pattern on the trailing edge of exhaust nozzles, are being implemented on modern jet engines. The technology reduces jet noise for ‘separate-flow’ nozzles used on newer jet aircraft engines. The purpose of this paper is to describe the development of this technology, starting with studies of ‘tabs' in the 1980's and 1990's. The tabs, essentially chevrons with more aggressive penetration, were studied in those early years with a focus on mixing enhancement in jets. Observations from experimentalists in connection with mixing enhancement and plume signature reduction suggested that there might also be a noise benefit. In the mid-nineties, these devices, with mild penetration to minimize thrust loss, were first seriously explored for aircraft engine noise reduction purposes. Prompted by a strong need for jet noise reduction, the study became a joint NASA/industry effort that ultimately matured the chevron technology to production by mid-2000's. The process is an example of how fundamental studies over decades eventually migrate to application but often take a concerted effort.