This paper describes some recent Computational Aeroacoustics (CAA) simulations of problems of pra... more This paper describes some recent Computational Aeroacoustics (CAA) simulations of problems of practical importance. Many previous CAA studies have emphasized the development of algorithms and their application to relatively simple model problems. Examples of computational aeroacoustic calculations are given for ducted fans, rotors, cavities, engine inlet liners, and jets. The need for three-dimensional, non-linear simulations and the feasibility of such solutions on high performance parallel computers is emphasized.
An aeroacoustic prediction scheme has been developed for landing gear noise. The method is design... more An aeroacoustic prediction scheme has been developed for landing gear noise. The method is designed to handle the complex landing gear geometry of current and future aircraft. The gear is represented by a collection of subassemblies and simple components that are modeled using acoustic elements. These acoustic elements are generic, but generate noise representative of the physical components on a landing gear. The method sums the noise radiation from each component of the undercarriage in isolation accounting for interference with adjacent components through an estimate of the local upstream and downstream flows and turbulence intensities. The acoustic calculations are made in the code LGMAP, which computes the sound pressure levels at various observer locations. The method can calculate the noise from the undercarriage in isolation or installed on an aircraft for both main and nose landing gear. Comparisons with wind tunnel and flight data are used to initially calibrate the method...
The Journal of the Acoustical Society of America, 2021
The goal of the present investigation is to study the effect of using fluid inserts for noise con... more The goal of the present investigation is to study the effect of using fluid inserts for noise control at high exhaust temperatures by performing a sequence of large eddy simulations on a typical military-style nozzle, both with and without fluid inserts, at jet inlet total temperature ratios of 2.5, 5, and 7. An exact physics-based splitting of the jet flow-field into its hydrodynamic, acoustic, and thermal components reveals clear evidence of a reduction in the radiation efficiency of Mach waves from the controlled jet. This effect is far more pronounced at afterburner conditions, where the location of the maximum noise reduction is observed to shift upstream with increase in jet temperature, thus matching the maximum location of the jet OASPL directivity. Moreover, the maximum noise reduction achieved at afterburner conditions exceeds that obtained at lower exhaust temperatures. This is encouraging and shows that the effectiveness of the fluid inserts improves with an increase in ...
This paper describes some personal background and a few of the technical achievements of Professo... more This paper describes some personal background and a few of the technical achievements of Professor Dennis K. McLaughlin, who has been my colleague at Penn State since 1986. I have known Dennis for much longer than this, and I credit him with recommending that I consider an academic career. This paper contains contributions from Dennis’s family, in particular his wife Connie, and from his current and former students and colleagues. I hope that these recollections will make a fitting introduction to this journal volume compiled in Dennis’s honor.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2019
Supersonic jets, such as the ones used in high-performance military aircraft, have both downstrea... more Supersonic jets, such as the ones used in high-performance military aircraft, have both downstream and upstream noise components due to the large-scale turbulent structures and the presence of shock cells in the jet plume. The fluid insert technology is a noise reduction method that has been shown to effectively reduce both these noise components. This paper analyses the unsteady flow changes associated with different fluid insert configurations with a goal of helping to understand the detailed noise reduction mechanisms. Using direct cross-correlations of the near-field data with the far-field microphone signals, it is found that even the use of a single injector as a fluid insert helps break up the large-scale structures of the flow. However, a more azimuthally distributed blowing is required to reduce the upstream broadband shock-associated noise (BBSAN). Addition of upstream injectors at each azimuthal location further enhances the BBSAN reduction. Decomposition of the jet flow-...
This paper describes some of the issues that must be addressed in the use of Computational Aeroac... more This paper describes some of the issues that must be addressed in the use of Computational Aeroacoustics (CAA) for the solution of problems of practical importance. Solutions to some of these difficulties are also given. Previous studies have only emphasized the development of algorithms and their application to relatively simple model problems. The particular issues addressed in this paper include: the computational resources required for CAA calculations; grid selection; boundary treatments; equation and algorithm selection; artificial dissipation; Kirchhoff methods; and, post-processing. Examples of computational aeroacoustic calculations are given for ducted fans and jets. The need for three-dimensional, non-linear simulations and the feasibility of such solutions on high performance parallel computers is emphasized
The Journal of the Acoustical Society of America, 2008
Landing gear noise is one of the most important sources of airframe noise. But it is the most dif... more Landing gear noise is one of the most important sources of airframe noise. But it is the most difficult to predict. The difficulty is that the landing gear is made up of components of substantially different scales. The small-scale features such as tubes and hoses are known to contribute to the landing gear noise, especially in the mid to high frequency range. Existing semi-empirical models are only reliable for the range of landing gear geometries for which test data are available. The present paper describes a component-based landing gear noise prediction model. The method uses an application of simple, fast, and scalable models called acoustic elements that are used to represent the complex landing gear geometry with a high level of geometric detail. Extensions to an earlier model developed by the authors is described, including the replacement of the original time domain approach with a frequency domain method. The local mean flow is also taken into account through the use of lo...
The Journal of the Acoustical Society of America, 1990
Broadband shock associated noise, in supersonic jets operating off-design, is generated by the in... more Broadband shock associated noise, in supersonic jets operating off-design, is generated by the interaction of large-scale structures in the jet mixing layer and the quasiperiodic shock cell structure of the jet. In this work, the shock cell structure of supersonic jets with noncircular exit geometry is modeled using a linear analysis. The analysis requires the solution of the equations of hydrodynamic stability for zero frequency. The model takes into account the finite thickness of the jet shear layer using realistic velocity and density profiles. The effects of the shear layer turbulence are included by incorporating eddy-viscosity terms. The numerical method involves the transformation of the cross section of a given jet to a rectangular computational domain using a series of conformal mappings. A pseudospectral hybrid scheme is used in the computational domain to set up the finite-differencing scheme. The variation of the pressure fluctuation with downstream distance is given fo...
This paper describes some recent Computational Aeroacoustics (CAA) simulations of problems of pra... more This paper describes some recent Computational Aeroacoustics (CAA) simulations of problems of practical importance. Many previous CAA studies have emphasized the development of algorithms and their application to relatively simple model problems. Examples of computational aeroacoustic calculations are given for ducted fans, rotors, cavities, engine inlet liners, and jets. The need for three-dimensional, non-linear simulations and the feasibility of such solutions on high performance parallel computers is emphasized.
An aeroacoustic prediction scheme has been developed for landing gear noise. The method is design... more An aeroacoustic prediction scheme has been developed for landing gear noise. The method is designed to handle the complex landing gear geometry of current and future aircraft. The gear is represented by a collection of subassemblies and simple components that are modeled using acoustic elements. These acoustic elements are generic, but generate noise representative of the physical components on a landing gear. The method sums the noise radiation from each component of the undercarriage in isolation accounting for interference with adjacent components through an estimate of the local upstream and downstream flows and turbulence intensities. The acoustic calculations are made in the code LGMAP, which computes the sound pressure levels at various observer locations. The method can calculate the noise from the undercarriage in isolation or installed on an aircraft for both main and nose landing gear. Comparisons with wind tunnel and flight data are used to initially calibrate the method...
The Journal of the Acoustical Society of America, 2021
The goal of the present investigation is to study the effect of using fluid inserts for noise con... more The goal of the present investigation is to study the effect of using fluid inserts for noise control at high exhaust temperatures by performing a sequence of large eddy simulations on a typical military-style nozzle, both with and without fluid inserts, at jet inlet total temperature ratios of 2.5, 5, and 7. An exact physics-based splitting of the jet flow-field into its hydrodynamic, acoustic, and thermal components reveals clear evidence of a reduction in the radiation efficiency of Mach waves from the controlled jet. This effect is far more pronounced at afterburner conditions, where the location of the maximum noise reduction is observed to shift upstream with increase in jet temperature, thus matching the maximum location of the jet OASPL directivity. Moreover, the maximum noise reduction achieved at afterburner conditions exceeds that obtained at lower exhaust temperatures. This is encouraging and shows that the effectiveness of the fluid inserts improves with an increase in ...
This paper describes some personal background and a few of the technical achievements of Professo... more This paper describes some personal background and a few of the technical achievements of Professor Dennis K. McLaughlin, who has been my colleague at Penn State since 1986. I have known Dennis for much longer than this, and I credit him with recommending that I consider an academic career. This paper contains contributions from Dennis’s family, in particular his wife Connie, and from his current and former students and colleagues. I hope that these recollections will make a fitting introduction to this journal volume compiled in Dennis’s honor.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2019
Supersonic jets, such as the ones used in high-performance military aircraft, have both downstrea... more Supersonic jets, such as the ones used in high-performance military aircraft, have both downstream and upstream noise components due to the large-scale turbulent structures and the presence of shock cells in the jet plume. The fluid insert technology is a noise reduction method that has been shown to effectively reduce both these noise components. This paper analyses the unsteady flow changes associated with different fluid insert configurations with a goal of helping to understand the detailed noise reduction mechanisms. Using direct cross-correlations of the near-field data with the far-field microphone signals, it is found that even the use of a single injector as a fluid insert helps break up the large-scale structures of the flow. However, a more azimuthally distributed blowing is required to reduce the upstream broadband shock-associated noise (BBSAN). Addition of upstream injectors at each azimuthal location further enhances the BBSAN reduction. Decomposition of the jet flow-...
This paper describes some of the issues that must be addressed in the use of Computational Aeroac... more This paper describes some of the issues that must be addressed in the use of Computational Aeroacoustics (CAA) for the solution of problems of practical importance. Solutions to some of these difficulties are also given. Previous studies have only emphasized the development of algorithms and their application to relatively simple model problems. The particular issues addressed in this paper include: the computational resources required for CAA calculations; grid selection; boundary treatments; equation and algorithm selection; artificial dissipation; Kirchhoff methods; and, post-processing. Examples of computational aeroacoustic calculations are given for ducted fans and jets. The need for three-dimensional, non-linear simulations and the feasibility of such solutions on high performance parallel computers is emphasized
The Journal of the Acoustical Society of America, 2008
Landing gear noise is one of the most important sources of airframe noise. But it is the most dif... more Landing gear noise is one of the most important sources of airframe noise. But it is the most difficult to predict. The difficulty is that the landing gear is made up of components of substantially different scales. The small-scale features such as tubes and hoses are known to contribute to the landing gear noise, especially in the mid to high frequency range. Existing semi-empirical models are only reliable for the range of landing gear geometries for which test data are available. The present paper describes a component-based landing gear noise prediction model. The method uses an application of simple, fast, and scalable models called acoustic elements that are used to represent the complex landing gear geometry with a high level of geometric detail. Extensions to an earlier model developed by the authors is described, including the replacement of the original time domain approach with a frequency domain method. The local mean flow is also taken into account through the use of lo...
The Journal of the Acoustical Society of America, 1990
Broadband shock associated noise, in supersonic jets operating off-design, is generated by the in... more Broadband shock associated noise, in supersonic jets operating off-design, is generated by the interaction of large-scale structures in the jet mixing layer and the quasiperiodic shock cell structure of the jet. In this work, the shock cell structure of supersonic jets with noncircular exit geometry is modeled using a linear analysis. The analysis requires the solution of the equations of hydrodynamic stability for zero frequency. The model takes into account the finite thickness of the jet shear layer using realistic velocity and density profiles. The effects of the shear layer turbulence are included by incorporating eddy-viscosity terms. The numerical method involves the transformation of the cross section of a given jet to a rectangular computational domain using a series of conformal mappings. A pseudospectral hybrid scheme is used in the computational domain to set up the finite-differencing scheme. The variation of the pressure fluctuation with downstream distance is given fo...
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