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This work explores the possibility of reducing the dominant noise source in a rectangular supersonic jet by enhancing its interaction with other coherent modes. As a first step before running Large-Eddy Simulations, we use Lineari...
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This work explores the possibility of reducing the dominant noise source in a rectangular supersonic jet by enhancing its interaction with other coherent modes. As a first step before running Large-Eddy Simulations, we use Linearized Euler Equations (LEE) to provide the transverse profiles of the various flow perturbation parameters across the jet and normalize these profiles such that it is a function of the Strouhal number and local momentum thickness. This, along with other appropriate transverse shape assumptions enable us to reduce the full governing equations into a set of ordinary differential equations (ODE) describing the interaction among the various coherent modes in the jet as well as with the mean flow and background fine-scale random turbulence. This work is an extension of previous works for a compressible shear layer, but the theory is extended into 3D with the use of LEE instead of the Linear Stability Theory to obtain the transverse shape of the coherent structure. ODE solutions are presented for the case of fundamental-subharmonic interactions between Strouhal numbers 0.20 and 0.10. It is concluded that adding the subharmonic can reduce the fundamental at an optimal initial phase angle and when both initial amplitudes are large.
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The availability and proliferation of small unmanned aircraft systems has provided engineers with the opportunity to gain hands on experience with aircraft in a manner that was previously limited to institutions and companies with...
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The availability and proliferation of small unmanned aircraft systems has provided engineers with the opportunity to gain hands on experience with aircraft in a manner that was previously limited to institutions and companies with large budgets. Even though the scope of these development programs are at their minimum, it is still challenging to simultaneously learn the skills required to develop an autonomous air vehicle while also applying the lessons to a physical system. In addition, current systems typically require a multidisciplinary team of engineering types to be successful in a short academic term. In this paper, a method for streamlining the software and hardware development of an unmanned aerial vehicle is developed and allows engineers with no specific background in electrical or computer engineering to leverage the power of Matlab~?/Simulink~? to develop, simulate, and ultimately flight test a system within an academic term using a very low cost autopilot system. Specific focus has been spent during the development of this tool on obfuscating the computer and electrical sciences from the problem so that engineers may concentrate on the more abstract concepts relevant to their field of study. In addition to a detailed description regarding the development of these tools, this paper presents simulation and flight testing results of the integrated system. An LQR based control law was successfully implemented and demonstrated in flight ultimately allowing the aircraft to navigate a course of waypoints autonomously. As a result of the successful development, the tool has been made available in the public domain for widespread distribution and hopeful collaboration with other aspiring developers.
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摘要 :
The availability and proliferation of small unmanned aircraft systems has provided engineers with the opportunity to gain hands on experience with aircraft in a manner that was previously limited to institutions and companies with...
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The availability and proliferation of small unmanned aircraft systems has provided engineers with the opportunity to gain hands on experience with aircraft in a manner that was previously limited to institutions and companies with large budgets. Even though the scope of these development programs are at their minimum, it is still challenging to simultaneously learn the skills required to develop an autonomous air vehicle while also applying the lessons to a physical system. In addition, current systems typically require a multidisciplinary team of engineering types to be successful in a short academic term. In this paper, a method for streamlining the software and hardware development of an unmanned aerial vehicle is developed and allows engineers with no specific background in electrical or computer engineering to leverage the power of Matlab~®/Simulink~® to develop, simulate, and ultimately flight test a system within an academic term using a very low cost autopilot system. Specific focus has been spent during the development of this tool on obfuscating the computer and electrical sciences from the problem so that engineers may concentrate on the more abstract concepts relevant to their field of study. In addition to a detailed description regarding the development of these tools, this paper presents simulation and flight testing results of the integrated system. An LQR based control law was successfully implemented and demonstrated in flight ultimately allowing the aircraft to navigate a course of waypoints autonomously. As a result of the successful development, the tool has been made available in the public domain for widespread distribution and hopeful collaboration with other aspiring developers.
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Understanding wall-jets is of utmost importance in modern engineering, where applications in thermal protection, combustion, flow control and noise generation are numerous. It can be seen as being composed of two canonical flows: ...
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Understanding wall-jets is of utmost importance in modern engineering, where applications in thermal protection, combustion, flow control and noise generation are numerous. It can be seen as being composed of two canonical flows: a boundary layer and a free mixing flow. In this paper, the focus is turned to the modulation of turbulence in weakly compressible isothermal wall-jets, when subject to changes in the jet-inlet conditions. Direct Numerical Simulations (DNS) of wall-jets are carried out using PyFR, a Python based computational fluid dynamics framework.22 Analysis of mean profiles and turbulence quantities response to carefully designed excitation profiles will be presented, as well as changes in coherent structures of the turbulent flow. Of particular interest is the relation between the Kelvin-Helmholtz instability and the modulation of turbulence in both the outer and the inner-layer. Finally, scaling similarities in the inner and outer layer will be discussed.
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摘要 :
Understanding wall-jets is of utmost importance in modern engineering, where applications in thermal protection, combustion, flow control and noise generation are numerous. It can be seen as being composed of two canonical flows: ...
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Understanding wall-jets is of utmost importance in modern engineering, where applications in thermal protection, combustion, flow control and noise generation are numerous. It can be seen as being composed of two canonical flows: a boundary layer and a free mixing flow. In this paper, the focus is turned to the modulation of turbulence in weakly compressible isothermal wall-jets, when subject to changes in the jet-inlet conditions. Direct Numerical Simulations (DNS) of wall-jets are carried out using PyFR, a Python based computational fluid dynamics framework.22 Analysis of mean profiles and turbulence quantities response to carefully designed excitation profiles will be presented, as well as changes in coherent structures of the turbulent flow. Of particular interest is the relation between the Kelvin-Helmholtz instability and the modulation of turbulence in both the outer and the inner-layer. Finally, scaling similarities in the inner and outer layer will be discussed.
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