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Newsletter  2014.12  Index

Theme : "Mechanical Engineering Congress, 2014 Japan (MECJ-14) Part 2"

  1. Preface
    (T. Sanada, H. Yokoyama, I. Kinefuchi)
  2. High Knudsen number flows (To micro-gas flows from rarefied gas flows)
    Tomohide NIIMI (Nagoya University)
  3. Workshop on the new horizon in advanced thermo-fluid measurements including cooperation with numerical simulations
    Toshiyuki HAYASE (Tohoku University)
  4. Flow measurements of electrically charged nanoparticles (Ion and tunnel currents)
    Kentaro DOI, Satoyuki KAWANO (Osaka University)
  5. Development of surface pressure fluctuation measurement technique for identification of aerodynamic sound source of a rotational fan
    Akiyoshi IIDA (Toyohashi University of Technology)
  6. Possibility of thrombus detection in extracorporeal blood flow channel using process tomography
    Achyut SAPKOTA, Takuto FUSE (Chiba University), Osamu MARUYAMA (AIST), Masahiro TAKEI (Chiba University)
  7. The recent case examples of thermo-fluid measurement using high-speed camera
    Joji KUWABARA (Photron Ltd.)

 

Development of Surface Pressure Fluctuation Measurement Technique for Identification of Aerodynamic Sound Source of a Rotational Fan


Akiyoshi Iida

Toyohashi University of Technology

 

Abstract

In order to clarify the generation mechanism of aerodynamic noise from axial flow fans, unsteady pressure fluctuation on the surface of blades were measured by time resolved Pressure Sensitive Paint based on micro-material slurry (MS-PSP). The frequency resolution of the developed PSP is up to 300Hz and the sensitivity is almost the same as the conventional PSP.

We also developed image-rotator apparatus composed of an image-rotation prism and MS-PSP system. By using this rotating prism synchronized with the rotation of the fan, we can capture an image that is stationary relative to the moving objects. The results showed that the strong pressure fluctuations were observed around the tip of blade at the suction side. Since the dominant noise sources of axial fans are located around tip of the blades, the present result is reasonable and it reveals the measurements of PSP were identified aerodynamic noise source on the surface of the axial fan. It indicates that the pressure fluctuation measurement with MS-PSP and the image-rotation prism will help to identify the sound source of aerodynamic noise.

Figure 1 shows the principle of the rotating image prism. When an image is taken through this prism, the picture become upside down. Moreover, an inclined angle of the image is twice of that of tilting angle of the prism. By utilizing this property, the image via a rotating prism, when the rotational speed of a prism is set to the half rotational speed of rotational object, the image of the rotational object can be captured as stationary image. By using this rotating prism synchronized with the rotation of the fan, we can capture an image that is stationary relative to the moving objects. In PSP measurements, since the accuracy of the PSP may affect the relative positional relationship between the CCD camera and the target object, correction of the relative position of the camera is required by the measurement of moving objects.  In this reason, the measurement of rotating objects such as fan, in usually, the phase averaged methods are utilized.  For this limitation, it is difficult to measure the instantaneous pressure.  In contrast, it is possible to suppress the effect of the correction of the position by using the present method.

Figure 2 shows the axial flow fan and measurement system for moving object with PSP. The present system consists with basic system of PSP measurement (CCD-Camera, UV-LED array and PSP coating material) and an image-rotator apparatus composed of an image-rotation prism.

Figure 3 (a) showed surface pressure distiribution of the rotating fan. The pressure fluctuation was large around the leading-edge of the blade. In general, it is known that the pressure fluctuations near the leading edge at the suction side of the fan generate large aerodynamic noise. It seems to be that result of the present measurement is reasonable to appropriate the general knowledge of aerodynamic noise. Because the results of this study is limited to qualitative results, quantitative evaluation of pressure fluctuations and aerodynamic sound source is difficult. However, the strong pressure fluctuations can be seen in the distal portion of the fan which is corresponds to the dominant noise sources, we may predict the noise source distribution through the PSP measurements. In this work, we show the possibility of measurement of the pressure fluctuation on the fan blade by utilizing a rotational-prism and PSP.

In order to clarify the generation mechanism of aerodynamic noise from axial flow fans, unsteady pressure fluctuation on the surface of blades were measured by time resolved pressure sensitive paint based on the micro slurry (MS-PSP). The MS-PSP is breakthrough technique to overcome the time resolution problems of PSP measurements. We also developed image-rotator apparatus composed of an image-rotation prism and MS-PSP system. By using this rotating prism synchronized with the rotation of the fan, we can capture an image that is stationary relative to the moving objects.  This technique resolved the correction problems of relative relationship between the CCD camera and moving objects.  To utilize this system for the unsteady pressure measurement of the rotational blades of an axial fan, we have carried out the measurement of the pressure fluctuations on the blades.  The results showed that the strong pressure fluctuations were observed around the tip of blade at the suction side. This region was almost the same as the dominant sound source of the axial fan.  It revealed that the pressure measurements of PSP were identified aerodynamic noise source on the surface of the axial fan.  It indicates that the pressure fluctuation measurement with MS-PSP and the image-rotation prism will help to identify the sound source of aerodynamic noise.

 

Key words

PSP, Pressure fluctuation, Aerodynamic nose

 

Figures


Fig. 1 Principle of image rotating prism


Fig. 2 Schematics and picture of PSP System for moving object


(a) Experiment (PSP)            (b)Simulation (LES)
Fig. 3 Pressure distribution on the surface of fan blade measured by PSP 

Last update: 12.15.2014