Organized Streamwise Vorticity on Convex Surfaces With Particular Reference to Turbine Blades

Gostelow, J. P.; Mahallati, Ali; Carscallen, W. E.; Rona, Aldo

doi:10.2514/6.2010-904

Cited by 5 publications

(7 citation statements)

References 21 publications

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“…The lowspeed streaks near to the blade surface are also observed on the suction surface at positive incidence, implying the presence of contra-rotating vortex pairs on a convex surface. Similar structures have been found on turbine blades, and a recent summary of the evidence for their existence has been presented by Gostelow et al [41].…”

Section: Positive Incidencementioning

confidence: 72%

Large Eddy Simulation of a Controlled Diffusion Compressor Cascade

McMullan

Page

2010

Flow Turbulence Combust

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In this research a Controlled Diffusion (CD) compressor cascade stator blade is simulated at a Reynolds number of ∼ 700, 000, based on inflow velocity and chord length, using Large Eddy Simulation (LES). A wide range of flow inlet angles are computed, including conditions near the design angle, and at high negative and positive incidence. At all inlet angles the surface pressure distributions are well-predicted by the LES. Near the design angle the computed suction side boundary layer thickness agrees well with experimental data, whilst the pressure side boundary layer is poorly predicted due to the inability of LES to capture natural boundary layer transition on the present grid. A good estimation of the loss is computed near the design angle, whilst at both high positive and negative incidences the loss is less well predicted owing to discrepancies between the computed and experimental boundary layer thickness. At incidences above the design angle a laminar separation bubble forms near the leading edge of the suction surface, which undergoes a transition to turbulence. Similar behaviour is noted on the pressure surface at negative incidence. At high negative incidence contra-rotating vortex pairs are found to form around the leading edge inThe authors would like to thank Rolls-Royce plc and the UK Technology Strategy Board for the funding this work under the CFMS Core Programme (TP/L3001H). The simulations in this study were performed on HECToR, the UK National Supercomputing Facility, under the UKAAC-2 Framework, EPSRC grant number EP/F005954/1. response to an unsteady stagnation line across the span of the blade. Such structures are not apparent in time-averaged statistical data due to their highly-transient nature.

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Section: Positive Incidencementioning

confidence: 72%

Large Eddy Simulation of a Controlled Diffusion Compressor Cascade

McMullan

Page

2010

Flow Turbulence Combust

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“…Surface flow visualization by Mahallati, as reported by Gostelow et al 1 , indicated strong and persistent streamwise vortical structures on the convex suction surface, as shown by the representative visualization in Fig. 1.…”

Section: Introductionmentioning

confidence: 79%

“…Halstead 6 has shown that the structures can persist through the turbulent boundary layer to the trailing edge. These fine-scale streaky structures may persist through shock interactions, laminar separation bubbles, the transition region and well into the turbulent layer 1 . Figure 2 gives an enlarged view of the vortical streaks towards the trailing edge of the turbine blade suction surface.…”

Section: Introductionmentioning

confidence: 99%

Stationary and Traveling Vortical Structures on Swept Cylinders and Turbine Blades

Gostelow

Rona

Garrett

et al. 2013

43rd Fluid Dynamics Conference

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Suction surface flow visualization on turbine blades at subsonic and transonic speeds showed robust streamwise streaks on a lengthy time-average basis. The normal flow past a circular cylinder is a more canonical case and testing was undertaken at high speeds on a 38 mm diameter cylinder and at low speeds on a 152 mm diameter cylinder. The lateral spacing between streaks on cylinders had been predicted by Kestin and Wood and the present tests gave excellent agreement with their theory. Although their work was related to unswept circular cylinders it also provides an excellent benchmark for sweep effects on cylinders and turbomachinery blading. The observations of streaks on turbine blades and unswept cylinders provided a firm basis for referencing the influence of sweep. Experiments on a circular cylinder were performed over a range of sweep angles from zero to 61 o giving results for lateral spacing and angular orientation of the streaks. At high-sweep angles the results are consistent with those of Poll. The introduction of sweep brings consideration of a wide range of instabilities; streamwise and crossflow structures are present on the suction surface of turbine blades. Although the available information on fine structures comes from surface flow visualization, work is now progressing on hot wire measurements away from the surface. The aim is to demonstrate the relationship between the structures and the surface traces. Analysis of the data is complemented by ongoing theoretical work. It is also hoped to provide information on the changing behavior of the vertical structures as the sweep angle is increased. The streamwise disturbance in the unswept case was found to be stationary in nature and to be resilient, often persisting from leading edge to trailing edge. Crossflow instability becomes more significant as sweep is increased. It grows aggressively and rapidly, being predominantly of a traveling nature, and has a major role to play in the transition process. The observed streaks could be of particular concern for the thermal design of turbine blades. It is hoped to give designers confidence about the flow regimes they might anticipate for a given sweep angle and particularly of when and how the aggressive crossflow instability mode is likely to be encountered. Nomenclature

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“…Surface flow visualization photographs have been analyzed from the work of a number of published experiments on blading. When examined in the same way as the surface flow visualization from the NRC cascade, two results from compressor blading 2,3 and four from turbine blading 4,11,12,13 were accessible. Figure 4 shows that these also gave reasonable agreement with the Kestin and Wood theory and experiments.…”

Section: Streamwise Vorticity Flow Visualization and Stability Thmentioning

confidence: 99%

“…Designers generally assume that streamwise vorticity of this kind is confined to these concave pressure surfaces. The authors have observed streamwise vorticity on suction surfaces, both experimentally 4 and computationally 5,6 . In this paper examples of this streamwise vorticity on convex surfaces will be considered.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Streamwise Vorticity on Transition in the Presence of Sweep

Gostelow

Garrett

Jean

2011

41st AIAA Fluid Dynamics Conference and Exhibit

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Experimental observations and theoretical predictions of streamwise vorticity on circular cylinders in crossflow and on turbine blades are considered. The observations on cylinders confirm earlier predictions and this forms a firm basis for referencing other measurements and predictions of vortical behavior. It also results directly in a correlation for predicting the spanwise wavelength of streamwise vortices on the convex surfaces of turbomachine blades. Highly resolved Large Eddy Simulation has shown that fine scale organized streamwise vorticity may exist on the convex surfaces of turbine and compressor blading and is predictable. For a turbine blade with a blunt leading edge the streamwise vorticity may persist on a time-average basis to influence the entire suction surface at suitably low Reynolds numbers typical of aircraft cruise conditions. The results emphasize the enormous computing resource required to resolve the flow on a routine basis for design purposes. It is demonstrated computationally that streamwise vorticity interacts with spanwise vorticity in leading edge bubbles to promote early transition and bubble closure. Time resolution is required to capture the flow complexity that is fundamental for an understanding of the physical behavior of the laminar boundary layer and its separation and transition. A narrow spanwise strip does not allow the streamwise vorticity to settle into the organized pattern. For streamwise vorticity to become organized, an adequate spanwise domain and run duration for time averaging are also essential. Any accurate treatment of laminar boundary layers at low Reynolds numbers needs to be performed three dimensionally and with a sufficiently fine spanwise spacing and duration of run to resolve streamwise vortical structures. Sweep of the body, wing or blade poses special problems. Not least is a serious lack of information on even the most basic cases. An attempt is made to relate the streamwise vorticity studied by Kestin and Wood to the more aggressive crossflow instability studied by Poll. More research is needed if designers are to be confident about the flow regimes they might expect to prevail for a given sweep angle. Nomenclature D Cylinder diameter n Amplification factor in inception prediction Re Reynolds number Tu Free-stream turbulence level u Velocity component in x direction x, y, z Coordinate directions    Angle between normal to the inflow and axis of the body    Spanwise spacing between vortex pairs  ___________________________________________________________________________________

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Organized Streamwise Vorticity on Convex Surfaces With Particular Reference to Turbine Blades

Cited by 5 publications

References 21 publications

Large Eddy Simulation of a Controlled Diffusion Compressor Cascade

Large Eddy Simulation of a Controlled Diffusion Compressor Cascade

Stationary and Traveling Vortical Structures on Swept Cylinders and Turbine Blades

The Influence of Streamwise Vorticity on Transition in the Presence of Sweep

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