Abstract
This paper describes an experimental investigation of the interaction noise in a jet impacting isolated aerofoils. The authors conducted the study in a low-speed wind tunnel ending in an anechoic chamber, and focussed on the tip region of two types of isolated low speed axial fan cambered aerofoils. The authors set the Mach number, Reynolds number and blade incidence angles in a static frame of reference to reproduce a flow field condition kinematically similar to that in the rotating frame. They correlated far-field noise measurements with near-field pressure measurements which they took at different chord-wise positions in the blade’s tip region. The aim was to find, by means of a cross correlation technique, a causal relationship between the aerodynamic sources in the tip region and noise emissions in order to establish the role of aerofoil self-noise associated with turbulent structures which turbulent inflow and blade tip geometry interaction produced.
Highlights
The research presented in this paper is part of an on-going noise reduction research stream aimed at developing the necessary technology to meet increasingly restrictive noise regulations and anticipated noise standards for low-speed axial turbomachinery
This paper describes an experimental investigation of the interaction noise in a jet impacting isolated aerofoils
5 Concluding Remarks The authors have experimentally investigated the change in the noise sources which two different aerofoils produce in a turbulent round jet and summarised the effect of the noise emission
Summary
The research presented in this paper is part of an on-going noise reduction research stream aimed at developing the necessary technology to meet increasingly restrictive noise regulations and anticipated noise standards for low-speed axial turbomachinery. Literature recognises the importance of the noise that originates from the interaction of unsteady disturbances at leading and trailing edges of an aerofoil, in fan or compressor blades, as a fundamental contributor to a rotor’s overall acoustic emission. The ingestion of turbulent flow sheared by aerofoil trailing or leading edges is a source of aerodynamically produced noise. The acoustic analogy which Lighthill [1] developed stated that the turbulent fluctuations in the free space are inefficient noise radiators at low flow Mach numbers, due to the turbulent sources’ quadrupolar-type character from which the radiated acoustic intensity through this region scales with the Mach number’s eighth power.
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