Natural Transition Phenomena on an Axial Compressor Blade

Hughes, J. D.; Walker, G. J.

doi:10.1115/1.1351816

Cited by 36 publications

(12 citation statements)

References 29 publications

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“…It does, however, also enhance the growth rate of Tollmien-Schlichting (TS) waves and, as a result, can cause early transition. Indeed Hughes and Walker [11] observed growth of discrete instability waves upstream of transition in a compressor case. Additionally, the free-stream turbulence and wakes can alter the breakdown of TS waves.…”

Section: The Influence Of Adverse Pressure Gradientmentioning

confidence: 98%

Direct Computations of Boundary Layers Distorted by Migrating Wakes in a Linear Compressor Cascade

Zaki

Wissink

Durbin

et al. 2009

Flow Turbulence Combust

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A Direct Numerical Simulation (DNS) of flow in the V103 Low-Pressure (LP) compressor cascade with incoming wakes was performed. The computational geometry was chosen largely in accordance with the setup of the experiments performed by Hilgenfeld and Pfitzner (J Turbomach 126: [493][494][495][496][497][498][499][500] 2004) at the University of the Armed Forces in Munich. The computations were carried out on the NEC-SX8 in Stuttgart using 64 processors and 85 million grid points. The incoming wakes stemmed from a separate DNS of incompressible flow around a circular cylinder with a Reynolds number of Re d = 3300 (based on mean inflow velocity and cylinder diameter). The boundary layer along the suction surface of the blade was found to separate and roll up due to a Kelvin-Helmholtz instability triggered by the periodically passing wakes. Inside the rolls further transition to turbulence was found to occur. The boundary-layer flow along the pressure surface did not separate, instead it underwent by-pass transition.

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Section: The Influence Of Adverse Pressure Gradientmentioning

confidence: 98%

Direct Computations of Boundary Layers Distorted by Migrating Wakes in a Linear Compressor Cascade

Zaki

Wissink

Durbin

et al. 2009

Flow Turbulence Combust

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“…In many turbomachinery flows, this natural transition route is bypassed by other mechanisms; nevertheless, the TS instability can play an important role in the ultimate breakdown to transition, particularly in compressors (e.g. Hughes & Walker 2001).…”

Section: Inherent Instabilitiesmentioning

confidence: 99%

Unsteady boundary-layer transition in low-pressure turbines

2011

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This paper examines the transition process in a boundary layer similar to that present over the suction surfaces of aero-engine low-pressure (LP) turbine blades. This transition process is of significant practical interest since the behaviour of this boundary layer largely determines the overall efficiency of the LP turbine. Modern 'high-lift' blade designs typically feature a closed laminar separation bubble on the aft portion of the suction surface. The size of this bubble and hence the inefficiency it generates is controlled by the transition between laminar and turbulent flow in the boundary layer and separated shear layer. The transition process is complicated by the inherent unsteadiness of the multi-stage machine: the wakes shed by one blade row convect through the downstream blade passages, periodically disturbing the boundary layers. As a consequence, the transition to turbulence is multi-modal by nature, being promoted by periodic and turbulent fluctuations in the free stream and the inherent instabilities of the boundary layer. Despite many studies examining the flow behaviour, the detailed physics of the unsteady transition phenomena are not yet fully understood. The boundary-layer transition process has been studied experimentally on a flat plate. The opposing test-section wall was curved to impose a streamwise pressure distribution typical of modern high-lift LP turbines over the flat plate. The presence of an upstream blade row has been simulated by a set of moving bars, which shed wakes across the test section inlet. Further upstream, a grid has been installed to elevate the free-stream turbulence to a level believed to be representative of multi-stage LP turbines. Extensive particle imaging velocimetry (PIV) measurements have been performed on the flat-plate boundary layer to examine the flow behaviour. In the absence of the incoming bar wakes, the grid-generated free-stream turbulence induces relatively weak Klebanoff streaks in the boundary layer which are evident as streamwise streaks of low-velocity fluid. Transition is promoted by the streaks and by the inherent inflectional (Kelvin-Helmholtz (KH)) instability of the separation bubble. In unsteady flow, the incoming bar wakes generate stronger Klebanoff streaks as they pass over the leading edge, which convect downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The region of amplified streaks convects in a similar manner to a classical turbulent spot: the leading and trailing edges travel at around 88% and 50% of the free-stream velocity, respectively. The strongest disturbances travel at around 70% of the free-stream velocity. The wakes induce a second type of disturbance as they pass over the separation bubble, in the form of short-span KH structures. Both the streaks and the KH structures contribute to the early wake-induced transition. The KH structures are similar to those observed in the simulation of separated flow transition with high free-stream turbulence by McAuliffe & Yaras (ASME Unsteady ...

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“…Both compressor and turbine performance can be affected by transition. The present study was largely motivated by the former: Hughes and Walker (2001) inferred from an analysis of experimental data that an interaction between Tollmien-Schlichting waves and free-stream turbulence occurs prior to transition on compressor blades. They processed data from a low speed compressor cascade and identified a frequency component that satisfied the Tollmien-Schlichting dispersion relation.…”

Section: Introductionmentioning

confidence: 99%