Alex Lau - Academia.edu (original) (raw)
Papers by Alex Lau
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
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19th AIAA/CEAS Aeroacoustics Conference, 2013
Procedia Engineering, 2010
This paper proposes inflow and outflow boundary conditions for direct computation of airfoil nois... more This paper proposes inflow and outflow boundary conditions for direct computation of airfoil noise under the influence of impinging gusts with a particular interest in the high frequency response. The proposed boundary conditions are based on an existing zonal sponge technique that has been used mostly to attenuate outgoing disturbances and absorb reflections from computational boundaries. A modified form of the sponge technique is presented in this paper in order to specify an incoming disturbance. The proposed boundary conditions still maintain the genuine non-reflective features that lead to accurate calculations of far-field sound intensity and directivity. It is also shown that the proposed boundary conditions enable the use of a significantly smaller domain size, and hence fewer grid cells, than used in conventional airfoil calculations, which enables the calculation of high-frequency gust-airfoil noise at a much lower computational cost. The proposed boundary conditions are validated against CAA (computational aeroacoustics) benchmark solutions after a variety of parametric tests, through which an optimal combination of the domain size, sponge thickness and a sponge coefficient is obtained for the highest efficiency. The proposed boundary conditions yield more accurate and consistent solutions particularly at the far field than the conventional ones. Further applications to high-frequency gust responses are performed to observe and demonstrate significant changes in the sound intensity and directivity varying with different frequencies and gust incidence angles.
Procedia IUTAM, 2010
... Aeroacoustics (CAA) for Aircraft Noise Prediction CAA boundary conditions for airfoil noise d... more ... Aeroacoustics (CAA) for Aircraft Noise Prediction CAA boundary conditions for airfoil noise due to high-frequency gusts Jae Wook Kim*, Alex SH Lau, Neil D ... m mm ffbfffff for 2&2 max = ii , (9) = + ++ 3 1 2112 )2( m miimimiiiii fffafffff for 33 max ii , (10) where fi = fifi is the ...
Procedia Engineering, 2010
This paper proposes inflow and outflow boundary conditions for direct computation of airfoil nois... more This paper proposes inflow and outflow boundary conditions for direct computation of airfoil noise under the influence of impinging gusts with a particular interest in the high frequency response. The proposed boundary conditions are based on an existing zonal sponge technique that has been used mostly to attenuate outgoing disturbances and absorb reflections from computational boundaries. A modified form of the sponge technique is presented in this paper in order to specify an incoming disturbance. The proposed boundary conditions still maintain the genuine non-reflective features that lead to accurate calculations of far-field sound intensity and directivity. It is also shown that the proposed boundary conditions enable the use of a significantly smaller domain size, and hence fewer grid cells, than used in conventional airfoil calculations, which enables the calculation of high-frequency gust-airfoil noise at a much lower computational cost. The proposed boundary conditions are validated against CAA (computational aeroacoustics) benchmark solutions after a variety of parametric tests, through which an optimal combination of the domain size, sponge thickness and a sponge coefficient is obtained for the highest efficiency. The proposed boundary conditions yield more accurate and consistent solutions particularly at the far field than the conventional ones. Further applications to high-frequency gust responses are performed to observe and demonstrate significant changes in the sound intensity and directivity varying with different frequencies and gust incidence angles.
Aiaa Journal, 2010
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Journal of Sound and Vibration, 2013
High-order accurate numerical simulations are performed to investigate the effects of wavy leadin... more High-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil-gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (λ g ) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA=λ g and the noise reduction is significant for LEA=λ g ≥0:3. The present results also suggest that any two different cases with the same LEA=λ g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1:0 ≤LEW=λ g ≤1:5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise.
AIAA Journal, 2010
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48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
RefDoc Refdoc est un service / is powered by. ...
19th AIAA/CEAS Aeroacoustics Conference, 2013
Procedia Engineering, 2010
This paper proposes inflow and outflow boundary conditions for direct computation of airfoil nois... more This paper proposes inflow and outflow boundary conditions for direct computation of airfoil noise under the influence of impinging gusts with a particular interest in the high frequency response. The proposed boundary conditions are based on an existing zonal sponge technique that has been used mostly to attenuate outgoing disturbances and absorb reflections from computational boundaries. A modified form of the sponge technique is presented in this paper in order to specify an incoming disturbance. The proposed boundary conditions still maintain the genuine non-reflective features that lead to accurate calculations of far-field sound intensity and directivity. It is also shown that the proposed boundary conditions enable the use of a significantly smaller domain size, and hence fewer grid cells, than used in conventional airfoil calculations, which enables the calculation of high-frequency gust-airfoil noise at a much lower computational cost. The proposed boundary conditions are validated against CAA (computational aeroacoustics) benchmark solutions after a variety of parametric tests, through which an optimal combination of the domain size, sponge thickness and a sponge coefficient is obtained for the highest efficiency. The proposed boundary conditions yield more accurate and consistent solutions particularly at the far field than the conventional ones. Further applications to high-frequency gust responses are performed to observe and demonstrate significant changes in the sound intensity and directivity varying with different frequencies and gust incidence angles.
Procedia IUTAM, 2010
... Aeroacoustics (CAA) for Aircraft Noise Prediction CAA boundary conditions for airfoil noise d... more ... Aeroacoustics (CAA) for Aircraft Noise Prediction CAA boundary conditions for airfoil noise due to high-frequency gusts Jae Wook Kim*, Alex SH Lau, Neil D ... m mm ffbfffff for 2&2 max = ii , (9) = + ++ 3 1 2112 )2( m miimimiiiii fffafffff for 33 max ii , (10) where fi = fifi is the ...
Procedia Engineering, 2010
This paper proposes inflow and outflow boundary conditions for direct computation of airfoil nois... more This paper proposes inflow and outflow boundary conditions for direct computation of airfoil noise under the influence of impinging gusts with a particular interest in the high frequency response. The proposed boundary conditions are based on an existing zonal sponge technique that has been used mostly to attenuate outgoing disturbances and absorb reflections from computational boundaries. A modified form of the sponge technique is presented in this paper in order to specify an incoming disturbance. The proposed boundary conditions still maintain the genuine non-reflective features that lead to accurate calculations of far-field sound intensity and directivity. It is also shown that the proposed boundary conditions enable the use of a significantly smaller domain size, and hence fewer grid cells, than used in conventional airfoil calculations, which enables the calculation of high-frequency gust-airfoil noise at a much lower computational cost. The proposed boundary conditions are validated against CAA (computational aeroacoustics) benchmark solutions after a variety of parametric tests, through which an optimal combination of the domain size, sponge thickness and a sponge coefficient is obtained for the highest efficiency. The proposed boundary conditions yield more accurate and consistent solutions particularly at the far field than the conventional ones. Further applications to high-frequency gust responses are performed to observe and demonstrate significant changes in the sound intensity and directivity varying with different frequencies and gust incidence angles.
Aiaa Journal, 2010
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Journal of Sound and Vibration, 2013
High-order accurate numerical simulations are performed to investigate the effects of wavy leadin... more High-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil-gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (λ g ) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA=λ g and the noise reduction is significant for LEA=λ g ≥0:3. The present results also suggest that any two different cases with the same LEA=λ g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1:0 ≤LEW=λ g ≤1:5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise.
AIAA Journal, 2010
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