Detection of Unsteady Boundary Layer Transition Using Three Experimental Methods

Richter, Kai; Wolf, Christian; Gardner, Anthony Donald; Merz, Christoph B.

doi:10.2514/6.2016-1072

Cited by 21 publications

(42 citation statements)

References 32 publications

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“…16). Gardner and Richter (2015) and Richter et al (2016) also measured pressures corresponding to c p > 0 near the trailing edge on the same airfoil. In both studies it was observed that the spatial extent for values of c p > 0 expands towards chord-wise locations further upstream at decreasing incident angles.…”

Section: Variation Of Rotating Frequencymentioning

confidence: 90%

Single-shot pressure-sensitive paint lifetime measurements on fast rotating blades using an optimized double-shutter technique

et al. 2017

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A pressure-sensitive paint (PSP) system is presented to measure global surface pressures on fast rotating blades. It is dedicated to solve the problem of blurred image data employing the single-shot lifetime method. The efficient blur reduction capability of an optimized double shutter imaging technique is demonstrated omitting error-prone post-processing or laborious de-rotation setups. The system is applied on Mach-scaled DSA-9A helicopter blades in climb at various collective pitch settings and blade tip Mach-and chord Reynolds numbers (M tip = 0.29−0.57; Re tip = 4.63− 9.26 • 10 5). Temperature effects in the PSP are corrected by a theoretical approximation validated against measured temperatures using temperature-sensitive paint (TSP) on a separate blade. Ensemble averaged PSP-results are comparable to pressure-tap data on the same blade to within 250 Pa. Resulting pressure maps on the blade suction side reveal spatially high resolved flow features such as the leading edge suction peak, footprints of blade-tip vortices and evidence of laminar-turbulent boundary-layer (BL) transition. The findings are validated by a separately conducted BL transition measurement by means of TSP and numerical simulations using a 2D coupled Euler/boundary-layer code. Moreover, the principal ability of the single-shot technique to capture unsteady flow phenomena is stressed revealing three-dimensional pressure fluctuations at stall.

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Section: Variation Of Rotating Frequencymentioning

confidence: 90%

Single-shot pressure-sensitive paint lifetime measurements on fast rotating blades using an optimized double-shutter technique

et al. 2017

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“…7 Comparison between measured and simulated blade loading for steady test cases at f rotor = 23.6 Hz and v ∞ = 4.9 m∕s Fig. 8 Intermittency correction function against transition onset and comparison to 2D airfoil data from Richter et al (2015) (Schlichting and Gersten 2017), which therefore explains the distribution of Δ 50% in Fig. 8.…”

Section: Steady Boundary-layer Transitionmentioning

confidence: 95%

“…8. Richter et al (2015) measured the full intermittency region on a 2D pitching DSA-9A airfoil suction side with hot-films at M = 0.3 and Re = 1.8 × 10 6 . Their results are added to Fig.…”

Section: Steady Boundary-layer Transitionmentioning

confidence: 99%

“…The processed DIT data, displayed by the solid and dashed lines for t∕T = 0.317 and t∕T = 0.683 , were used to find the circled signal peaks. According to Richter et al (2016) and Gardner et al (2017), the DIT peak locations are equivalent to the positions corresponding to 50% turbulence intermittency. The DIT peak location is also at the position where the cycle-to-cycle RMS pressure transducer signal peaks (according to the so-called c p method by Gardner and Richter 2015), and therefore considered as the transition position (x∕c) tr in this work.…”

Section: Unsteady Boundary-layer Transitionmentioning

confidence: 99%

“…The basic idea is to subtract two infrared images taken with a short time delay in order to detect the intermediate transition motion. Raffel and Merz (2014) have demonstrated the measurement principle in proof-of-concept experiments, Richter et al (2016) validated the technique against hot-films and dynamic pressure sensors, and Wolf et al (2019) optimized DIT for various experimental conditions.…”

Section: Introductionmentioning

confidence: 99%

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Unsteady boundary-layer transition measurements and computations on a rotating blade under cyclic pitch conditions

et al. 2020

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The presented work tackles the lack of experimental investigations of unsteady laminar-turbulent boundary-layer transition on rotor blades at cyclic pitch actuation, which are important for accurate performance predictions of helicopters in forward flight. Unsteady transition positions were measured on the blade suction side of a four-bladed subscale rotor by means of non-intrusive differential infrared thermography (DIT). Experiments were conducted at different rotation rates corresponding to Mach and Reynolds numbers at 75% rotor radius of up to M 75 = 0.21 and Re 75 = 3.3 × 10 5 and with varying cyclic blade pitch settings. The setup allowed transition to be measured across the outer 54% of the rotor radius. For comparison, transition was also measured using conventional infrared thermography for steady cases with collective pitch settings only. The study is complemented by numerical simulations including boundary-layer transition modeling based on semi-empirical criteria. DIT results reveal the upstream and downstream motion of boundary-layer transition during upstroke and downstroke, a reasonable comparison to experimental results obtained using the already established c p method, and noticeable agreement with numerical simulations. The result is the first systematic study of unsteady boundary-layer transition on a rotor suction side by means of DIT including a comparison to numerical computations. Abbreviations AHD Boundary-layer transition criterion according to Arnal, Habiballah and Delcourt CFD Computational fluid dynamics DIT Differential infrared thermography

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Unsteady Boundary Layer Transition Detection with Local Infrared Thermography

Mertens

Wolf

Gardner

2019

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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Detection of Unsteady Boundary Layer Transition Using Three Experimental Methods

Cited by 21 publications

References 32 publications

Single-shot pressure-sensitive paint lifetime measurements on fast rotating blades using an optimized double-shutter technique

Single-shot pressure-sensitive paint lifetime measurements on fast rotating blades using an optimized double-shutter technique

Unsteady boundary-layer transition measurements and computations on a rotating blade under cyclic pitch conditions

Unsteady Boundary Layer Transition Detection with Local Infrared Thermography

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