Rotating Blade Stall Maps Measured by Differential Infrared Thermography

Raffel, Markus; Gardner, Anthony Donald; Schwermer, Till; Merz, Christoph B.; Weiss, Armin; Braukmann, Johannes N.; Wolf, Christian

doi:10.2514/1.j055452

Cited by 11 publications

(8 citation statements)

References 11 publications

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“…However, good optical access and sufficient space are required. If the rotor is tested in propeller configuration, the mirror has to be installed preferably in "off-axis" configuration (Raffel et al, 2017) causing additional challenges in order to synchronize the rotation rates of the mirror setup and the rotor. Both methods have recently been compared in more detail by Pandey et al (2016).…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…The figure can therefore be interpreted as a stall map of test case C1. Similar ideas were implemented by Gardner et al (2016) and Raffel et al (2017), who deduced stall maps using the standard deviation of thermal difference images of a 2D pitching airfoil and a rotating blade in a dynamic-stall condition. The experimental results in Fig.…”

Section: Test Case C1mentioning

confidence: 99%

“…However, these techniques are limited in their spatial resolution and tuft images leave residual ambiguities in their interpretation. Gardner et al (2016) used infrared thermography to optically detect dynamic stall on pitching airfoils and the technique was applied by Raffel et al (2017) to deduce rotating blade stall maps that indicate geometrical regions on the blade where stalled flow occurs. Although the stall map presented in the latter study marked a breakthrough, the signal was rather weak and significant spatial averaging was needed to finally detect stalled flow regimes as a function of the blade radius and the pitch phase.…”

Section: Introductionmentioning

confidence: 99%

Dynamic-stall measurements using time-resolved pressure-sensitive paint on double-swept rotor blades

et al. 2021

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The study presents an optimized pressure-sensitive paint (PSP) measurement system that was applied to investigate unsteady surface pressures on recently developed double-swept rotor blades in the rotor test facility at the German Aerospace Center (DLR) in Göttingen. The measurement system featured an improved version of a double-shutter camera that was designed to reduce image blur in PSP measurements on fast rotating blades. It also comprised DLR’s PSP sensor, developed to capture transient flow phenomena (iPSP). Unsteady surface pressures were acquired across the outer 65% of the rotor blade with iPSP and at several radial blade sections by fast-response pressure transducers at blade-tip Mach and Reynolds numbers of $$\mathrm {M}_\mathrm{tip} = 0.282-0.285$$ M tip = 0.282 - 0.285 and $$\mathrm {Re}_\mathrm{tip}= 5.84-5.95 \times 10^5$$ Re tip = 5.84 - 5.95 × 10 5 . The unique experimental setup allowed for scanning surface pressures across the entire pitch cycle at a phase resolution of $${0.225}\,{\mathrm{deg}}$$ 0.225 deg azimuth for different collective and cyclic-pitch settings. Experimental results of both investigated cyclic-pitch settings are compared in detail to a delayed detached eddy simulation using the flow solver FLOWer and to flow visualizations from unsteady Reynolds-averaged Navier–Stokes (URANS) computations with DLR’s TAU code. The findings reveal a detailed and yet unseen insight into the pressure footprint of double-swept rotor blades undergoing dynamic stall and allow for deducing “stall maps”, where confined areas of stalled flow on the blade are identifiable as a function of the pitch phase. Graphical abstract

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“…layer transition on different setups, from pitching airfoils to large scale rotor test rigs [24,25]. A variant of the DIT method has been used to observe static and dynamic stall [26,27]. Wolf et al [18] recently performed an optimization of the DIT method for unsteady transition detection on a pitching airfoil model, based on the recommendations given in [17].…”

Section: Infrared Thermography For Unsteady Boundary Layer Transition...mentioning

confidence: 99%

Advanced infrared thermography data analysis for unsteady boundary layer transition detection

Mertens

Wolf

Gardner

et al. 2019

Meas. Sci. Technol.

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Advanced data processing methods for detecting unsteady boundary layer transition in periodic aerodynamic processes by means of infrared thermography measurements are presented. The thermal radiation emitted from the heated suction surface of a pitching airfoil model in subsonic flow is measured with an infrared camera. The unsteady boundary layer transition location is detected by analyzing the difference in the infrared radiation signal over short periods of time with differential infrared thermography (DIT). The DIT method is optimized and automated in the present study, which facilitates the extension of the part of the motion period where valid DIT transition measurements are produced. Additionally, a new infrared thermography data processing method is introduced in this study. The extraction of the extrema of the measured radiation signal at fixed locations on the model surface yields instants of the motion period that relate to the occurrence of boundary layer transition. The local infrared thermography (LIT) approach can be extended to measuring the twodimensional unsteady boundary layer transition front.

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Rotating Blade Stall Maps Measured by Differential Infrared Thermography

Cited by 11 publications

References 11 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

Dynamic-stall measurements using time-resolved pressure-sensitive paint on double-swept rotor blades

Advanced infrared thermography data analysis for unsteady boundary layer transition detection

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