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

Abstract

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

Dynamic Stall Investigation on a Rotating Semielastic Double-swept Rotor Blade at the Rotor Test Facility Göttingen

“…Moreover, unsteady surface pressure measurements by means of pressure-sensitive paint (iPSP) revealed first insights into the global pressure footprint of the innovative blade geometry while undergoing dynamic stall showing excellent agreement to numerical computations (Ref. 27). The focus of all previous dynamic stall investigations at the RTG was mainly with respect to rotor aerodynamics.…”

“…For more information about the iPSP setup, see Ref. 27. The axial inflow was measured using a Prandtl-probe in the nozzle.…”

“…A detailed explanation of the measurement technique, the applied iPSP sensor, the experimental setup and the data reduction is presented in Ref. 27. Therefore, only a brief summary is given here.…”

“…Selected iPSP results were presented previously in Ref. 27 with a focus on a comparison to numerical simulations. In this study, different iPSP results are shown and presented the context of aeroelastic measurements.…”

A dual-camera single-shot lifetime method with fully controllable exposure gates for pressure-sensitive paint measurements on fast-rotating surfaces

“…The rapid evolution of measurement techniques has enabled PSP to be applied to more challenging tasks [7] such as pressure measurement on fast-rotating surfaces. The advantage of wireless data acquisition (DAQ) has made PSP a powerful tool in applications such as helicopter rotors [8][9][10][11][12][13], compressor blades [14][15][16] and propulsion impellers [17][18][19]. However, two major challenges limit the applicability of PSP measurements on fastrotating surfaces.…”