A compact Ka-band monolithic microwave integrated circuit(MMIC) voltage controlled oscillator (VCO) with wide tuning range and high output power,which is based on GaAs PHEMT process,is presented.A method is introduced...A compact Ka-band monolithic microwave integrated circuit(MMIC) voltage controlled oscillator (VCO) with wide tuning range and high output power,which is based on GaAs PHEMT process,is presented.A method is introduced to reduce the chip size and to increase the bandwidth of operation.The procedure to design a MMIC VCO is also described here.The measured oscillating frequency of the MMIC VCO is 36±1.2GHz and the output power is 10±1dBm.The fabricated MMIC chip size is 1.3mm×1.0mm.展开更多
A monolithic clock-recovery circuit used in 622 Mb/s optical communication system is designed,which is based on the phase-locked loop theory,and uses bipolar transistor model.It overcomes the shortcoming of clock reco...A monolithic clock-recovery circuit used in 622 Mb/s optical communication system is designed,which is based on the phase-locked loop theory,and uses bipolar transistor model.It overcomes the shortcoming of clock recovery method based on filter,and implements monolithic clock-recovery IC.The designed circuits include phase detector,voltage-controlled oscillator and loop filter.Among them,the voltage-control oscillator is a modified two-stage ring oscillator,which provides quadrature clock signals and presents wide voltage-controlled range and high voltage-controlling sensitivity.展开更多
the system to DC voltage source as the core, AT89C52 MCU as the main controller, the output voltage to set the DC power supply through the keyboard, with a step function voltage to reality, the actual output value. Th...the system to DC voltage source as the core, AT89C52 MCU as the main controller, the output voltage to set the DC power supply through the keyboard, with a step function voltage to reality, the actual output value. This design is divided into four modules： SCM control and display module, digital to analog （D/A） conversion module, a constant voltage source module, output module. MCU control module as the core, the input signal is converted to digital quantity output; constant current source module voltage D/A conversion to analog conversion into constant pressure through a constant voltage circuit. The system has good reliability, high precision.展开更多
For a serious prediction of vibration characteristics of any structure, a detailed knowledge of the modal characteristic is essential. This is especially important for bladed turbine rotors. Mistuning of the blading o...For a serious prediction of vibration characteristics of any structure, a detailed knowledge of the modal characteristic is essential. This is especially important for bladed turbine rotors. Mistuning of the blading of a turbine rotor can appear due to manufacturing tolerances or because of the blading process itself due to unequal mounting of the blades into the disk. This paper investigates the mistuning of the individual blades of a low pressure turbine with respect to the effects mentioned above. Two different rotors with different aerodynamic design of the blades were investigated. The blades were mounted to the disk with a so-called hammer head root which is especially prone to mounting irregularities. For detailed investigations, the rotor was excited with a shaker system to detect the forced response behavior of the individual blades. The measurements were done with a laser vibrometer system. As the excitation of rotor structure was held constant during measurement, it was possible to detect the line of nodes and mode shapes as well. It could be shown that the assembly process has an influence on the mistuning. The data were analyzed and compared with numerical results. For this, different contact models and boundary conditions were used. The above described characterization of modal behavior of the rotor is the basis for the upcoming aeroelastic investigations and especially for the blade vibration measurements of the rotor, turning with design and off-design speeds.展开更多
Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The ...Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The resulting aerodynamic forces were interpolated to the finite element(FE) model through surface effect elements prior to conducting forced response calculations.Effects of axial gap on aerodynamic forces were studied. In addition, influence of axial gap on the response of the shrouded blade was compared with that on the response of the unshrouded blade. Results demonstrated that as the axial gap increases,time-averaged pressure on the blade surface changes very little, while the pressure fluctuations decrease significantly. Pressure and aerodynamic forces on the blade surface display periodic variation, and the vane passing frequency component is dominant.Amplitudes of aerodynamic forces decrease with increasing axial gap. Restricted by the shroud, deformation and response of shrouded blade are much lower than those of the unshrouded blade. The response of unshrouded blade shows obvious beat vibration phenomenon, while the response of the shrouded blade does not have this characteristic because the shroud restrains multiple harmonics. Blade response in time domain was converted to frequency domain using fast Fourier transformation(FFT).Results revealed that the axial gap mainly affects the forced harmonic at the vane passing frequency, while the other two harmonics at natural frequency are hardly affected. Amplitudes of the unshrouded blade response decrease as the axial gap increases, while amplitudes of the shrouded blade response change very little in comparison.展开更多
Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it ...Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it is possible to obtain higher pressure ratios compared to conventional compressors. However, it must be noted that imposing higher aerodynamic loads results in higher loss coemcients and deteriorates the overall performance. To avoid the loss increase, the boundary layer quality must be studied carefully over the blade suction surface. Employment of advanced shaped airfoils （like CDAs）, slotted blades or other boundary layer control methods has helped the de- signers to use higher aerodynamic loads on compressor blades. Tandem cascade is a passive boundary layer control method, which is based on using the flow momentum to control the boundary layer on the suction surface and also to avoid the probable separation caused by higher aerodynamic loads. In fact, the front pressure side flow momentum helps to compensate the positive pressure gradient over the aft blade＇s suction side. Also, in compari- son to the single blade stators, tandem variable stators have more degrees of freedom, and this issue increases the possibility of finding enhanced conditions in the compressor off-design performance. In the current study, a 3D design procedure for an axial flow tandem compressor stage has been applied to design a highly loaded stage. Following, this design is numerically investigated using a CFD code and the stage characteristic map is reported. Also, the effect of various stator stagger angles on the compressor performance and especially on the compressor surge margin has been discussed. To validate the CFD method, another known compressor stage is presented and its performance is numerically investigated and the results are compared with available experimental results.展开更多
An experimental study is conducted to improve an aft-loaded ultra-high-lift low pressure turbine(LPT) blade at low Reynolds number(Re) in steady state. The objective is to investigate the effect of blade roughness on ...An experimental study is conducted to improve an aft-loaded ultra-high-lift low pressure turbine(LPT) blade at low Reynolds number(Re) in steady state. The objective is to investigate the effect of blade roughness on the performance of LPT blade. The roughness is used as a passive flow control method which is to reduce total pressure loss and expand LPT operating margin. The experiment is performed on a low-speed cascade facility. 3 roughness heights and 3 deposit positions are investigated in the experiment which forms a large test matrix. A three-hole probe is used to detect flow aerodynamic performance and a hotwire probe is used to detect the characteristic of suction boundary layer. Regional roughness can suppress separation loss and bring fairly low turbulent dissipation loss. Detailed surveys near the blade surface shows that the loss reduction is due to the disappearance of separation bubble from the early transition onset.展开更多
文摘A compact Ka-band monolithic microwave integrated circuit(MMIC) voltage controlled oscillator (VCO) with wide tuning range and high output power,which is based on GaAs PHEMT process,is presented.A method is introduced to reduce the chip size and to increase the bandwidth of operation.The procedure to design a MMIC VCO is also described here.The measured oscillating frequency of the MMIC VCO is 36±1.2GHz and the output power is 10±1dBm.The fabricated MMIC chip size is 1.3mm×1.0mm.
文摘A monolithic clock-recovery circuit used in 622 Mb/s optical communication system is designed,which is based on the phase-locked loop theory,and uses bipolar transistor model.It overcomes the shortcoming of clock recovery method based on filter,and implements monolithic clock-recovery IC.The designed circuits include phase detector,voltage-controlled oscillator and loop filter.Among them,the voltage-control oscillator is a modified two-stage ring oscillator,which provides quadrature clock signals and presents wide voltage-controlled range and high voltage-controlling sensitivity.
文摘the system to DC voltage source as the core, AT89C52 MCU as the main controller, the output voltage to set the DC power supply through the keyboard, with a step function voltage to reality, the actual output value. This design is divided into four modules： SCM control and display module, digital to analog （D/A） conversion module, a constant voltage source module, output module. MCU control module as the core, the input signal is converted to digital quantity output; constant current source module voltage D/A conversion to analog conversion into constant pressure through a constant voltage circuit. The system has good reliability, high precision.
文摘For a serious prediction of vibration characteristics of any structure, a detailed knowledge of the modal characteristic is essential. This is especially important for bladed turbine rotors. Mistuning of the blading of a turbine rotor can appear due to manufacturing tolerances or because of the blading process itself due to unequal mounting of the blades into the disk. This paper investigates the mistuning of the individual blades of a low pressure turbine with respect to the effects mentioned above. Two different rotors with different aerodynamic design of the blades were investigated. The blades were mounted to the disk with a so-called hammer head root which is especially prone to mounting irregularities. For detailed investigations, the rotor was excited with a shaker system to detect the forced response behavior of the individual blades. The measurements were done with a laser vibrometer system. As the excitation of rotor structure was held constant during measurement, it was possible to detect the line of nodes and mode shapes as well. It could be shown that the assembly process has an influence on the mistuning. The data were analyzed and compared with numerical results. For this, different contact models and boundary conditions were used. The above described characterization of modal behavior of the rotor is the basis for the upcoming aeroelastic investigations and especially for the blade vibration measurements of the rotor, turning with design and off-design speeds.
文摘Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The resulting aerodynamic forces were interpolated to the finite element(FE) model through surface effect elements prior to conducting forced response calculations.Effects of axial gap on aerodynamic forces were studied. In addition, influence of axial gap on the response of the shrouded blade was compared with that on the response of the unshrouded blade. Results demonstrated that as the axial gap increases,time-averaged pressure on the blade surface changes very little, while the pressure fluctuations decrease significantly. Pressure and aerodynamic forces on the blade surface display periodic variation, and the vane passing frequency component is dominant.Amplitudes of aerodynamic forces decrease with increasing axial gap. Restricted by the shroud, deformation and response of shrouded blade are much lower than those of the unshrouded blade. The response of unshrouded blade shows obvious beat vibration phenomenon, while the response of the shrouded blade does not have this characteristic because the shroud restrains multiple harmonics. Blade response in time domain was converted to frequency domain using fast Fourier transformation(FFT).Results revealed that the axial gap mainly affects the forced harmonic at the vane passing frequency, while the other two harmonics at natural frequency are hardly affected. Amplitudes of the unshrouded blade response decrease as the axial gap increases, while amplitudes of the shrouded blade response change very little in comparison.
文摘Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it is possible to obtain higher pressure ratios compared to conventional compressors. However, it must be noted that imposing higher aerodynamic loads results in higher loss coemcients and deteriorates the overall performance. To avoid the loss increase, the boundary layer quality must be studied carefully over the blade suction surface. Employment of advanced shaped airfoils （like CDAs）, slotted blades or other boundary layer control methods has helped the de- signers to use higher aerodynamic loads on compressor blades. Tandem cascade is a passive boundary layer control method, which is based on using the flow momentum to control the boundary layer on the suction surface and also to avoid the probable separation caused by higher aerodynamic loads. In fact, the front pressure side flow momentum helps to compensate the positive pressure gradient over the aft blade＇s suction side. Also, in compari- son to the single blade stators, tandem variable stators have more degrees of freedom, and this issue increases the possibility of finding enhanced conditions in the compressor off-design performance. In the current study, a 3D design procedure for an axial flow tandem compressor stage has been applied to design a highly loaded stage. Following, this design is numerically investigated using a CFD code and the stage characteristic map is reported. Also, the effect of various stator stagger angles on the compressor performance and especially on the compressor surge margin has been discussed. To validate the CFD method, another known compressor stage is presented and its performance is numerically investigated and the results are compared with available experimental results.
基金Supported by National Natural Science Foundation of China(51206163 and 51306176)International S&T Cooperation Program of China,Project No.2013DFR61080
文摘An experimental study is conducted to improve an aft-loaded ultra-high-lift low pressure turbine(LPT) blade at low Reynolds number(Re) in steady state. The objective is to investigate the effect of blade roughness on the performance of LPT blade. The roughness is used as a passive flow control method which is to reduce total pressure loss and expand LPT operating margin. The experiment is performed on a low-speed cascade facility. 3 roughness heights and 3 deposit positions are investigated in the experiment which forms a large test matrix. A three-hole probe is used to detect flow aerodynamic performance and a hotwire probe is used to detect the characteristic of suction boundary layer. Regional roughness can suppress separation loss and bring fairly low turbulent dissipation loss. Detailed surveys near the blade surface shows that the loss reduction is due to the disappearance of separation bubble from the early transition onset.
