Correlation of flow path length to total pressure loss in diffuser flows

Abstract

This article studies the effect of changing the flow path length on development of total pressure loss in diffuser flows. The studies incorporate quasi-one-dimensional (conical diffuser), two-dimensional (linear blade cascade), and three-dimensional (annular blade cascade) flows. This article concludes that the consequence of decreasing the flow path length is to decrease total pressure loss, provided that the adverse streamwise pressure gradient remains subcritical. The loss calculation technique and measurement data published by Lieblein were post-processed in this article. On this basis, this article elaborates a method for estimating the total pressure loss as well as its modification due to change of flow path length in blade cascade flows. This method can contribute to preliminary axial flow rotor blade design. It was pointed out that, in comparison to free vortex design, controlled vortex design that is applied to straight axial flow rotor blades tends to represent an additional source of total pressure loss farther from the endwalls. This is due to elongation of the length of flow paths on the blade suction side, due to intensified radial outward flow. This adverse effect can be counterbalanced by incorporation of forward sweep in controlled vortex design, via shortening the flow paths on the suction side, without the beneficial features of the controlled vortex design being lost. This article presents a literature-based comparative case study to illustrate such loss-reducing effect of incorporating forward sweep in controlled vortex design, away from the endwalls.

An industrial onsite methodology for combined acoustic-aerodynamic diagnostics of axial fans, involving the phased array microphone technique

“…34 The intention of the authors is to seek a correlation between experiment-based indicators of local noise and loss, along the blade span. The SS BL, appearing as the dominant BNS in the bands of f mid ≤ 3150 Hz, plays a major role also in generation of aerodynamic loss, as noted in Vad 35 on the basis of literature references. Some recent techniques in BNS computation 24 relate the noise to the BL thickness.…”

“…Lieblein 36 established a strong correlation between the D diffusion factor 21,30,37 and the wake momentum thickness θ normalized by the blade chord c . In Vad, 35 the following empirical formula has been proposed for this correlation …”

Incorporation of forward blade sweep in preliminary controlled vortex design of axial flow rotors

“…As outlined in, e.g. Vad [ 1 , 2 ], CVD offers several benefits, such as, among others, realization of high specific performance, moderation of hub losses and outlet loss, and basis for obtainment of simple and easy-to-manufacture rotor geometry.…”

“…A blade is of forward sweep (FSW) if the sections of a straight datum blade are shifted parallel to their chord in such a way that a blade section under consideration is upstream of the neighbouring blade section at lower radius. It has been pointed out by the author that FSW is especially beneficial for the rotors of CVD, in terms of moderating the loss near the tip [ 1 ] as well as away from the endwalls [ 2 ].…”

Vibration and Noise of an Axial Flow Fan

“…This suggest that in the "free-inlet" case (no upstream obstruction of the flow), the rotor noise radiated toward the upstream direction is dominated by rotor "self-noise". In addition to noise generation, the suction side boundary layer plays a major role also in generation of aerodynamic loss [14].…”