# Simultaneous Pressure and Displacement Measurement on Helicopter Rotor Blades Using a Binocular Stereophotogrammetry PSP System

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Experimental Setup

#### 2.1. Rotor Test Stand and Model

_{2}particles and a small amount of polymer, was first applied. Platinum tetra (pentafluorophenyl) porphyrin (PtTFPP) was used as the pressure sensors and its solution in methanol was then air sprayed onto the binder layer. For the TSP blade, a tier of white paint was first utilized to increase the TSP signal level. Then, a mixture of clear coat and tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride (Ru(dpp)

_{3}) solution was air sprayed onto the white coat. The PSP and TSP occupied the area from 0.75 to 1 along the radial length, as presented in Figure 2. The rotational velocity was maintained at 840 rpm during the assay, which was a commonly used safe velocity, slightly lower than the maximum rated velocity. The blade tip velocity was 175.84 m/s, and the Mach quantity at the tip was 0.517.

#### 2.2. Measurement Setup

_{3}, two 600 nm long-pass filter were placed before the lens on these two cameras.

#### 2.3. Data Acquisition

_{2}/I

_{1}) represented the emission lifetimes and were inversely proportional to the local pressure and temperature, respectively. This relation is shown in Equation (1):

_{dark1}and I

_{dark2}. For each PSP image captured, including both reference and wind-on conditions, I

_{dark1}and I

_{dark2}were firstly subtracted from the corresponding original image. The following processing procedures in Figure 5 were then conducted. For the recording of the reference photos, the rotation velocity was 50 rpm and the collective pitch was 0°. Consequently, the effects of aerodynamical loading could be neglected. The flap and lag angles were hypothesized as 0°. It is noteworthy that the data collection rate of such a system (approximately 7 Hz) was lower than the rotor frequency (14 Hz), as it was restricted by the repetitive rates of these cameras.

## 3. Data Processing

#### 3.1. PSP Paint Calibration

#### 3.2. PSP Temperature Correction

_{RoR}) was first fitted with a quadratic curve. The TSP I

_{RoR}field and the effect of quadratic fitting are presented in Figure 8. In Figure 8a, the horizontal and vertical directions represent the radial and chord directions, respectively. Figure 8b presents the span-wise temperature distribution extracted and the effect of quadratic fitting at x/C = 0.5. At each radial location, 10 chordwise pixels in the middle of the blade were averaged to reduce the random measurement errors caused by paint non-uniformity and camera noise.

_{RoR_corr}fields according to the following equation:

_{RoR_PSP}and I

_{RoR_corr}are PSP I

_{RoR}before and after temperature correction, and m(T) is the ratio of temperature sensitiveness between PSP and TSP.

_{RoR_corr}fields and the pressure calibration results. During data processing, 15 marker points were applied near the edge of the blade for image registration. As there were no data available at these points, pressure was interpolated in a small area around each point to fill empty pixels.

#### 3.3. Binocular Stereophotogrammetry

**R T**), called the extrinsic parameters, is the rotation and translation which relates the world coordinate system to the camera coordinate system, and

**A**, called the intrinsic matrix, is given by

_{0}, y

_{0}) the coordinates of the principal point, f

_{x}and f

_{y}the equivalent focal length in image x and y axes, and γ the parameter describing the skewness of the two image axes.

_{1}and k

_{2}are the coefficients of the radial distortion.

## 4. Results and Discussion

#### 4.1. Results of Surface Pressure Measurement

#### 4.2. Results of Blade Displacement Measurement

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 6.**Comparison of PSP image in Gate 2. (

**a**)

**I**

_{2}under reference conditions. (

**b**)

**I**

_{2}at n = 840 rpm.

**Figure 7.**Calibration results for PSP and TSP. (

**a**) Pressure calibration. (

**b**) Temperature calibration.

**Figure 8.**TSP field from TSP (840 rpm, θ = 4°). (

**a**) TSP I

_{RoR}field of TSP blade. (

**b**) Span-wise temperature distribution extracted and effect of quadratic fitting at x/C = 0.5.

Collective Pitch (°) | Accuracy of Blade Targets (mm) |
---|---|

0 | 0.152 |

4 | 0.174 |

8 | 0.197 |

Average | 0.174 |

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## Share and Cite

**MDPI and ACS Style**

Wei, C.; Zuo, C.; Liao, X.; Li, G.; Jiao, L.; Peng, D.; Liang, L.
Simultaneous Pressure and Displacement Measurement on Helicopter Rotor Blades Using a Binocular Stereophotogrammetry PSP System. *Aerospace* **2022**, *9*, 292.
https://doi.org/10.3390/aerospace9060292

**AMA Style**

Wei C, Zuo C, Liao X, Li G, Jiao L, Peng D, Liang L.
Simultaneous Pressure and Displacement Measurement on Helicopter Rotor Blades Using a Binocular Stereophotogrammetry PSP System. *Aerospace*. 2022; 9(6):292.
https://doi.org/10.3390/aerospace9060292

**Chicago/Turabian Style**

Wei, Chunhua, Chenglin Zuo, Xianhui Liao, Guoshuai Li, Lingrui Jiao, Di Peng, and Lei Liang.
2022. "Simultaneous Pressure and Displacement Measurement on Helicopter Rotor Blades Using a Binocular Stereophotogrammetry PSP System" *Aerospace* 9, no. 6: 292.
https://doi.org/10.3390/aerospace9060292