Water Tunnel Flow Diagnostics of Wake Structures Downstream of a Model Helicopter Rotor Hub

Reich, David; Elbing, Brian R.; Berezin, Charles R.; Schmitz, Sven

doi:10.4050/jahs.59.032001

Cited by 9 publications

(33 citation statements)

References 15 publications

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“…However, the shape of the mean wake profile (nondimensionalized by the freestream speed) was unchanged between the two Reynolds numbers evaluated (Ref. 51), suggesting that the shed flow structures were similar in size and strength between both Reynolds numbers.…”

Section: Fig 2 Fairing Shapes Tested By Montana At Full-scale Reynomentioning

confidence: 92%

See 1 more Smart Citation

A Review of 60 Years of Rotor Hub Drag and Wake Physics: 1954–2014

Reich

Shenoy

Smith

et al. 2016

j am helicopter soc

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The rotor hub system is recognized as one of the primary contributors to helicopter parasite drag and is one of the inherent limiters to maximum helicopter forward-flight speed. Despite its importance for the performance of rotorcraft, complex bluff-body flows of the rotor hub have received only intermittent attention since the first studies in the 1950s. This work presents a comprehensive review of experimental and computational research over the past 60 years on rotor hub flows and describes the challenges associated with component and interference drag, effect of the hub near wake on pylon and fuselage flows, and the long-age wake of rotor hubs at high Reynolds number with the associated size and strength of flow structures that interact with the empennage. Computational technology is assessed as an emerging design tool for hub/pylon design, and, with its ability to capture downstream flow unsteadiness, empennage/tail surface aeroelasticity and controllability. The work concludes with recommendations of future experimental and computational evaluations to advance the community's understanding of rotor hub flows and mitigation of its adverse effects for future rotorcraft. Nomenclature Zvertical coordinate axis, m (positive upward) μ rotor advance ratio, U ∞ / R Rotor ν fluid kinematic viscosity, m 2 /s ρ fluid density, kg/m 3 rotor rotational speed, revolutions per minute 022007-2

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Section: Fig 2 Fairing Shapes Tested By Montana At Full-scale Reynomentioning

confidence: 92%

“…More details on the experimental setup, exact measurement locations, and uncertainty quantification can be found in Ref. 51. For additional details on the GTWT, see Ref.…”

Section: Fig 2 Fairing Shapes Tested By Montana At Full-scale Reynomentioning

confidence: 99%

A Review of 60 Years of Rotor Hub Drag and Wake Physics: 1954–2014

Reich

Shenoy

Smith

et al. 2016

j am helicopter soc

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“…Each rotor hub component was machined separately and assembled in varying configurations throughout the experiment. The basic model geometry was an identical, scaled-down version of that used in a previous study conducted in the PSU ARL 48-in.-diam test-section water tunnel [23], with the addition of several features. As shown in Fig.…”

Section: A Facility and Test Rigmentioning

confidence: 99%

“…This corresponds to approximately 33% of the full-scale Reynolds number for a large helicopter (e.g., Sikorsky S92 and Eurocopter EC225) at sea level and about 45% of the full-scale Reynolds number at an altitude of 10,000 ft. For a small helicopter (e.g., Robinson R44), this corresponds to approximately 75% of the full-scale Reynolds number at sea level and 70% of the full-scale Reynolds number at an altitude of 2000 ft. Also note that the values of Re hub achievable in the 12-in.-diam water tunnel are lower than that of the 48 in. Garfield Thomas Water Tunnel, used in a previous study [23].…”

Section: B Reynolds Number Scalingmentioning

confidence: 99%

Scaling and Configuration Effects on Helicopter Rotor Hub Interactional Aerodynamics

Reich

Willits

Schmitz

2017

Journal of Aircraft

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A 1:17 scale model of a notional rotor hub of a large helicopter was tested in the Pennsylvania State University Applied Research Laboratory 12 in. test-section water tunnel. Objectives of the experiment were to quantify the effects of Reynolds number, advance ratio, and hub geometry configuration on the drag and shed wake of the rotor hub. A range of flow conditions was tested, with hub-diameter-based Reynolds numbers ranging from 1.0 × 10 6 to 2.6 × 10 6 and advance ratios ranging from 0.2 to 0.6, as well as nonrotating cases. Five hub geometry configurations were tested with various combinations of components including blade stubs, spiders, scissors, the swashplate, pitch links, and beanie fairing. Measurements included the steady and unsteady hub drag and particle image velocimetry at two downstream locations. Results include time-averaged and phase-averaged analyses of the unsteady drag and wake velocity. A strong dependence of the steady and unsteady hub drag and wake on the advance ratio, Reynolds number, and configuration was observed, demonstrating the importance of adequate Reynolds number scaling for model helicopter rotor hub tests.

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“…Typical commercial recirculating water tunnels achieve a momentum thickness based Reynolds number (Re h ) on the order of 10 3 , which is slightly above that required for laminar to turbulent transition. This is not ideal for studying Reynolds number dependent turbulent flow phenomena, such as velocity profile modifications from drag reducing polymer solutions [1,2] or helicopter wake structures [3]. Consequently, much of this work is performed in extremely large government owned water tunnels such as the U.S. Navy Large Cavitation Channel (LCC) [4,5] or the Garfield Thomas Water Tunnel (GTWT) [6,7].…”

Section: Introductionmentioning

confidence: 99%

Design and Validation of a Recirculating, High-Reynolds Number Water Tunnel

Elbing

Daniel

Farsiani

et al. 2018

Journal of Fluids Engineering

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Commercial water tunnels typically generate a momentum thickness based Reynolds number (Reθ) ∼1000, which is slightly above the laminar to turbulent transition. The current work compiles the literature on the design of high-Reynolds number facilities and uses it to design a high-Reynolds number recirculating water tunnel that spans the range between commercial water tunnels and the largest in the world. The final design has a 1.1 m long test-section with a 152 mm square cross section that can reach speed of 10 m/s, which corresponds to Reθ=15,000. Flow conditioning via a tandem configuration of honeycombs and settling-chambers combined with an 8.5:1 area contraction resulted in an average test-section inlet turbulence level <0.3% and negligible mean shear in the test-section core. The developing boundary layer on the test-section walls conform to a canonical zero-pressure-gradient (ZPG) flat-plate turbulent boundary layer (TBL) with the outer variable scaled profile matching a 1/7th power-law fit, inner variable scaled velocity profiles matching the log-law and a shape factor of 1.3.

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Water Tunnel Flow Diagnostics of Wake Structures Downstream of a Model Helicopter Rotor Hub

Cited by 9 publications

References 15 publications

A Review of 60 Years of Rotor Hub Drag and Wake Physics: 1954–2014

A Review of 60 Years of Rotor Hub Drag and Wake Physics: 1954–2014

Scaling and Configuration Effects on Helicopter Rotor Hub Interactional Aerodynamics

Design and Validation of a Recirculating, High-Reynolds Number Water Tunnel

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