Abstract

We show that desired swirl distributions may be obtained in non-circular and non-cylindrical inlet ducts by tailored vane distributions designed with an a priori method, and further explain dominant physics for the spatial evolution of swirl in expanding or contracting ducts. Virginia Tech has developed the StreamVane™ device for producing swirl distortion, as well as the ScreenVane™ device for producing combined swirl and pressure distortions. Up to now, all StreamVane and ScreenVane devices have designed to fit in a right, circular cylindrical duct. This is usually the simplest geometry to use for testing the response (in terms of performance and stall margin changes, as well as aeromechanics) of turbofan engines to inlet distortion.

However, many potential applications exist for generating or removing swirl distortions in ducts that are not cylindrical. For example, turboshaft engines generally do not have a cylindrical inlet to install a StreamVane in front of. Yet, inlet distortion is still very relevant to the performance of the engine. With a non-cylindrical StreamVane, inlet distortions generated by various flight conditions can be tested in conjunction with the real aircraft inlet. Further applications exist both within and outside of the field of turbomachinery for flow conditioning purposes. Four separate conceptual designs were created and analyzed: a converging duct (nozzle), a diverging duct (diffuser), a square duct, and an annular duct. Twin vortex swirl profiles were specified for all of the cases except the annular duct, which was designed to create a single vortex.

However, in a real application, these swirl profiles would instead be specified by the end-user depending on what is required for the test. As in circular cylindrical StreamVanes, the end-user has the option of selecting any physically consistent swirl profile. All of the concept designs were checked with CFD analysis in ANSYS CFX. The square and annular StreamVanes showed comparable performance to a baseline StreamVane in a cylindrical duct (RMS errors of 1.5° or less). The StreamVanes placed in a nozzle and diffuser demonstrated that swirl patterns may also be created in converging and diverging ducts, and that the varying cross sectional area has a non-negligible influence on the development of the swirl profile. A simple explanation has been made for this altered flow development has been, and is shown to make good quantitative predictions of the changes in swirl with downstream location.

The demonstration of the capability to create StreamVanes for applications that do not use cylindrical ducts should open a variety of possibilities, while building on existing experiences.

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