Flow structure on a rotating wing: effect of radius of gyration

2014 ◽  
Vol 755 ◽  
pp. 83-110 ◽  
Author(s):  
M. Wolfinger ◽  
D. Rockwell
Keyword(s):  
Flow Structure ◽  
Leading Edge ◽  
Flow Patterns ◽  
Travel Distance ◽  
Stereoscopic Particle Image Velocimetry ◽  
Radius Of Gyration ◽  
Rossby Number ◽  
Vortex System ◽  
Vorticity Flux ◽  
Rotating Wing

AbstractThe flow structure on a rotating wing (flat plate) is characterized over a range of Rossby number $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Ro} = r_g/C$, in which $r_g$ and $C$ are the radius of gyration and chord of the wing, as well as travel distance $\mathit{Ro} = r_g \Phi /C$, where $\Phi $ is the angle of rotation. Stereoscopic particle image velocimetry (SPIV) is employed to determine the flow patterns on defined planes, and by means of reconstruction, throughout entire volumes. Images of the $Q$-criterion and spanwise vorticity, velocity and vorticity flux are employed to represent the flow structure. At low Rossby number, the leading-edge, tip and root vortices are highly coherent with large dimensionless values of $Q$ in the interior regions of all vortices and large downwash between these components of the vortex system. For increasing Rossby number, however, the vortex system rapidly degrades, accompanied by loss of large $Q$ within its interior and downstream displacement of the region of large downwash. These trends are accompanied by increased deflection of the leading-edge vorticity layer away from the surface of the wing, and decreased spanwise velocity and vorticity flux in the trailing region of the wing, which are associated with the degree of deflection of the tip vortex across the wake region. Combinations of large Rossby number $\mathit{Ro} =r_g/C$ and travel distance $r_g \Phi /C$ lead to separated flow patterns similar to those observed on rectilinear translating wings at high angle of attack $\alpha $. In the extreme case where the wing travels a distance corresponding to a number of revolutions, the highly coherent flow structure is generally preserved if the Rossby number is small; it degrades substantially, however, at larger Rossby number.

Flow structure on a simultaneously pitching and rotating wing

2014 ◽  
Vol 756 ◽  
pp. 354-383 ◽  
Author(s):  
M. Bross ◽  
D. Rockwell
Keyword(s):  
Flow Structure ◽  
Large Scale ◽  
Three Dimensional ◽  
Leading Edge ◽  
Tip Vortex ◽  
Pure Rotation ◽  
Large Scale Vortex ◽  
Edge Vortex ◽  
Vorticity Flux ◽  
Rotating Wing

AbstractA technique of particle image velocimetry is employed to characterize the three-dimensional flow structure on a wing subjected to simultaneous pitch-up and rotational motions. Distinctive vortical structures arise, relative to the well-known patterns on a wing undergoing either pure pitch-up or pure rotation. The features associated with these simultaneous motions include: stabilization of the large-scale vortex generated at the leading edge, which, for pure pitch-up motion, rapidly departs from the leading-edge region; preservation of the coherent vortex system involving both the tip vortex and the leading-edge vortex (LEV), which is severely degraded for pure rotational motion; and rapid relaxation of the flow structure upon termination of the pitch-up component, whereby the relaxed flow converges to a similar state irrespective of the pitch rate. Three-dimensional surfaces of iso-$\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{Q}$and helicity are employed in conjunction with sectional representations of spanwise vorticity, velocity and vorticity flux to interpret the flow physics.

Three-dimensional vortex structure on a rotating wing

2012 ◽  
Vol 707 ◽  
pp. 541-550 ◽  
Author(s):  
Cem A. Ozen ◽  
D. Rockwell
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Dimensional Structure ◽  
Radius Of Gyration ◽  
Leading Edge Vortex ◽  
Image Velocimetry ◽  
Edge Vortex ◽  
Vorticity Flux ◽  
Rotating Wing ◽  
Spanwise Flow

AbstractThe three-dimensional structure of the leading-edge vortex on a rotating wing is addressed using a technique of particle image velocimetry. Organized patterns of chordwise-oriented vorticity, which exist within the vortex, arise from the spanwise flow along the surface of the wing, which can attain a velocity the same order as the velocity of the wing at its radius of gyration. These patterns are related to the strength (circulation) and coherence of the tip and root vortices. The associated distributions of spanwise-oriented vorticity along the leading-edge vortex are characterized in relation to the vorticity flux and downwash along the wing.

Numerical Investigation of Passive Flow Control Using Wavy Blades in a Highly-Loaded Compressor Cascade

2018 ◽  
Author(s):  
Bo Wang ◽  
Yanhui Wu ◽  
Kai Liu
Keyword(s):  
Numerical Investigation ◽  
Flow Structure ◽  
Cross Flow ◽  
Leading Edge ◽  
Control Flow ◽  
Streamwise Vortices ◽  
Compressor Cascade ◽  
Control Effect ◽  
Suction Surface ◽  
Highly Loaded

Driven by the need to control flow separations in highly loaded compressors, a numerical investigation is carried out to study the control effect of wavy blades in a linear compressor cascade. Two types of wavy blades are studied with wavy blade-A having a sinusoidal leading edge, while wavy blade-B having pitchwise sinusoidal variation in the stacking line. The influence of wavy blades on the cascade performance is evaluated at incidences from −1° to +9°. For the wavy blade-A with suitable waviness parameters, the cascade diffusion capacity is enhanced accompanied by the loss reduction under high incidence conditions where 2D separation is the dominant flow structure on the suction surface of the unmodified blade. For well-designed wavy blade-B, the improvement of cascade performance is achieved under low incidence conditions where 3D corner separation is the dominant flow structure on the suction surface of the baseline blade. The influence of waviness parameters on the control effect is also discussed by comparing the performance of cascades with different wavy blade configurations. Detailed analysis of the predicted flow field shows that both the wavy blade-A and wavy blade-B have capacity to control flow separation in the cascade but their control mechanism are different. For wavy blade-A, the wavy leading edge results in the formation of counter-rotating streamwise vortices downstream of trough. These streamwise vortices can not only enhance momentum exchange between the outer flow and blade boundary layer, but also act as the suction surface fence to hamper the upwash of low momentum fluid driven by cross flow. For wavy blade-B, the wavy surface on the blade leads to a reduction of the cross flow upwash by influencing the spanwise distribution of the suction surface static pressure and guiding the upwash flow.

Influence of Leading Edge Fillet and Nonaxisymmetric Contoured Endwall on Turbine NGV Exit Flow Structure and Interactions With the Rim Seal Flow

2013 ◽  
Author(s):  
Özhan H. Turgut ◽  
Cengiz Camcı
Keyword(s):  
Flow Structure ◽  
Total Pressure ◽  
Guide Vane ◽  
Axial Flow ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Constant Thickness ◽  
Computational Evaluation ◽  
Nozzle Guide

Three different ways are employed in the present paper to reduce the secondary flow related total pressure loss. These are nonaxisymmetric endwall contouring, leading edge (LE) fillet, and the combination of these two approaches. Experimental investigation and computational simulations are applied for the performance assessments. The experiments are carried out in the Axial Flow Turbine Research Facility (AFTRF) having a diameter of 91.66cm. The NGV exit flow structure was examined under the influence of a 29 bladed high pressure turbine rotor assembly operating at 1300 rpm. For the experimental measurement comparison, a reference Flat Insert endwall is installed in the nozzle guide vane (NGV) passage. It has a constant thickness with a cylindrical surface and is manufactured by a stereolithography (SLA) method. Four different LE fillets are designed, and they are attached to both cylindrical Flat Insert and the contoured endwall. Total pressure measurements are taken at rotor inlet plane with Kiel probe. The probe traversing is completed with one vane pitch and from 8% to 38% span. For one of the designs, area averaged loss is reduced by 15.06%. The simulation estimated this reduction as 7.11%. Computational evaluation is performed with the rotating domain and the rim seal flow between the NGV and the rotor blades. The most effective design reduced the mass averaged loss by 1.28% over the whole passage at the NGV exit.

Endwall Heat Transfer Measurements in a Staggered Pin Fin Array With an Adiabatic Pin

2007 ◽  
Author(s):  
Forrest E. Ames ◽  
Chad A. Nordquist ◽  
Lindsay A. Klennert
Keyword(s):  
Heat Transfer ◽  
Turbulent Transport ◽  
Infrared Camera ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Vortex System ◽  
Flow Acceleration ◽  
Pin Fin ◽  
Pin Fin Array

Full surface endwall heat transfer distributions have been acquired in a staggered pin fin array with the use of an infrared camera. Values are presented at Reynolds numbers of 3000, 10,000 and 30,000 based on pin diameter and average velocity through adjacent pins. Average endwall Nusselt numbers agree closely with archival values at each Reynolds number. Locally averaged heat transfer levels show a substantial increase from the inlet through the first few rows and finally a nearly streamwise periodic condition in the second half of the eight row geometry. Increasing levels of heat transfer in the inlet region can be attributed to the leading edge vortex system, flow acceleration around pins, and the generation of turbulence. Distributions of turbulence intensity and turbulent scale are shown to help document the turbulent transport conditions through the array. Detailed endwall Nusselt number distributions are presented and compared at the three Reynolds numbers for the first four and last four rows. These detailed heat transfer distributions highlight the influence of the horseshoe vortex system in the entrance region and the wake generated turbulence throughout the pin fin array. Local velocity and turbulence distributions are presented together with local Stanton number and skin friction coefficient data to examine the aggressive nature of the turbulent mixing.

Influence of Flow Structure on Shaped Hole Film Cooling Performance

2010 ◽  
Author(s):  
Benoit Laveau ◽  
Reza S. Abhari
Keyword(s):  
Flow Structure ◽  
Thermal Performance ◽  
Turbine Blades ◽  
Density Ratio ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Infrared Measurements ◽  
Cylindrical Holes ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Shaped holes are used on modern turbine blades for their higher performance and greater lateral coolant spreading compared to classic streamwise angled holes. This study incorporates measurements and observations from a shaped hole geometry undertaken at ETH Zurich in which a row of laterally expanded diffusely shaped holes is compared to the classic row of streamwise round holes. Infrared measurements provide high-resolution data of the adiabatic effectiveness and three dimensional velocity measurements are carried out through stereoscopic Particle Image Velocimetry. Both experiments are run for similar operating conditions allowing a comparison to be made between the flow structure and the thermal performance. The adiabatic effectiveness is seen to be higher for shaped holes compared to cylindrical holes: in particular the laterally averaged values are higher due to a larger lateral spreading of the coolant. The work presented here shows the first results on the limited influence of the density ratio on the thermal performance. The performance is also influenced by the vortical structure. The typical counter-rotating vortex pair which is completed by another pair of anti-kidney vortices is observed with their strength being clearly reduced compared to the example with cylindrical holes. The doubled structure and the reduced strength change the behavior of the jet, explaining the higher performance of a jet with shaped holes. The vertical motion leading to lift-off is reduced, so the jet remains close to the surface even at high blowing rates. The goal of this article is to present data for the thermal performance and flow field of shaped holes and then explain the relationship between the two.

scholarly journals On the lift-optimal aspect ratio of a revolving wing at low Reynolds number

2018 ◽  
Vol 15 (143) ◽  
pp. 20170933 ◽  
Author(s):  
T. Jardin ◽  
T. Colonius
Keyword(s):  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Rossby Number ◽  
Subsequent Work ◽  
High Lift ◽  
Low Aspect Ratio ◽  
Axis Of Rotation ◽  
Edge Vortex ◽  
Convergent Solution

Lentink & Dickinson (2009 J. Exp. Biol. 212 , 2705–2719. ( doi:10.1242/jeb.022269 )) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

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