Effects of Periodic Inflow Unsteadiness on the Time-Averaged Velocity Field and Pressure Recovery of a Diffusing Bend With Strong Curvature

Abstract

This study examines the effects of periodic inflow unsteadiness on the flow development through fishtail-shaped diffusers utilized on small gas-turbine engines. In this application, periodic unsteadiness is caused by a jet-wake type of flow discharging from each passage of the centrifugal compressor impeller. The study consists of detailed measurements in a large-scale fishtail diffuser rig with a geometry that is typical of those used in small gas-turbine engines. Measurements of the transient velocity field have been performed at five cross-sectional planes throughout the diffuser using a miniature hot-wire probe with four wires. These measurements involve frequencies of inflow unsteadiness corresponding to design as well as off-design operating conditions. Results indicate significant effects of inflow unsteadiness at the low end of the tested frequencies on the time-averaged streamwise and cross-flow velocity fields in the diffuser. This is shown to translate into a notable impact on the pressure recovery. In addition to providing insight into the physics of this flow, the experimental results presented here constitute a detailed and accurate data set that can be used to validate computational-fluid-dynamics algorithms for this type of flow.

Investigation of two pipe diffuser configurations for a compact centrifugal compressor

“…In the current study, the design of the cross section of the fishtail diffuser was based on the investigations of Yaras 16,17 and Yaras and Orsi. 18 As shown in Figure 3, at the throat of the pipe diffuser, the cross section is circular and the centerline of the diffuser remains straight along a conical flow path. Then, the cross section becomes oblong, characterized by semi-circular ends attached by straight lines like an oval.…”

“…[11][12][13][14] Despite the extensive studies on pipe diffusers, few comprehensive results have been published addressing the complex flow characteristics in fishtail diffusers. [15][16][17][18] Although there are several ways to guide the flow from the pipe diffuser throat to the combustor inlet, it is difficult to address which configuration is more suitable, given that little discussion has been done to evaluate these methods. Additionally, there may also be a deswirler inside or outside the fishtail to create more uniform exit flow, but the flow and loss mechanisms within the deswirler have not yet been examined.…”

Dyfuzor rurkowy sprężarki promieniowej i osiowo-promieniowej

“…Układ wylotowy sprężarki z dyfuzorem rurkowym stanowi dyfuzor zakrzywiony -promieniowo--osiowy (ang. diffusing trumpet [11], fishtail-shaped diffuser, controlled-contour diffuser [12]). Rysunek 4. przedstawia trzy kanały dyfuzora rurkowego, których osie są styczne do okręgu zakreślonego promieniem R 2 w punktach A 1 , A 2 , A 3 .…”