HIGH FREQUENCY NOISE GENERATION IN SMALL AXIAL FLOW FANS

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

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High frequency noise modeling of SiGe HBTs using a direct parameter extraction technique

The 10th IEEE International Symposium on Electron Devices for Microwave and Optoelectronic Applications ◽

10.1109/edmo.2002.1174953 ◽

2003 ◽

Cited By ~ 3

Author(s):

U. Basaran ◽

M. Berroth

Keyword(s):

High Frequency ◽

Parameter Extraction ◽

Extraction Technique ◽

Frequency Noise ◽

High Frequency Noise ◽

Noise Modeling

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Bayesian deconvolution of gamma‐ray logs

Geophysics ◽

10.1190/1.1442270 ◽

1987 ◽

Vol 52 (11) ◽

pp. 1535-1546 ◽

Cited By ~ 5

Author(s):

Ping Sheng ◽

Benjamin White ◽

Balan Nair ◽

Sandra Kerford

Keyword(s):

High Frequency ◽

Gamma Ray ◽

Simulated Data ◽

Field Measurements ◽

Bayesian Optimization ◽

Frequency Noise ◽

High Frequency Noise ◽

Data Application ◽

Gamma Ray Detector ◽

Gamma Ray Log

The spatial resolution of gamma‐ray logs is defined by the length 𝓁 of the gamma‐ray detector. To resolve thin beds whose thickness is less than 𝓁, it is generally desirable to deconvolve the data to reduce the averaging effect of the detector. However, inherent in the deconvolution operation is an amplification of high‐frequency noise, which can be a detriment to the intended goal of increased resolution. We propose a Bayesian statistical approach to gamma‐ray log deconvolution which is based on optimization of a probability function which takes into account the statistics of gamma‐ray log measurements as well as the empirical information derived from the data. Application of this method to simulated data and to field measurements shows that it is effective in suppressing high‐frequency noise encountered in the deconvolution of gamma‐ray logs. In particular, a comparison with the least‐squares deconvolution approach indicates that the incorporation of physical and statistical information in the Bayesian optimization process results in optimal filtering of the deconvolved results.

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