Effect Of Axial Gap Research Articles

Investigation of the Effect of Axial Gap on the Mechanical Response of a Cartridge-Loaded CMDB Propellant Grain under Vibration Loads

In this study, the effect of the axial gap on the mechanical response of a cartridge-loaded propellant grain under vibration loads is investigated. The wide strain rate range of uniaxial compression tests ( 1.7 × 10 − 3 ~ 4 × 10 3 s − 1 ) on the composite modified double base (CMDB) propellant was carried out by using a universal testing machine, a hydraulic testing machine, and a split Hopkinson pressure bar system, respectively. A linear viscoelastic constitutive model of the CMDB propellant was developed by using the experimental measurements. The results show the studied CMDB propellant has a strong strain rate dependence, exhibiting an initial linear elasticity followed by a strain hardening region. The dynamic process of collision between the propellant grain and the motor case in the axial direction induced by vibration loads was simulated with the developed constitutive model by using the finite element method. The effects of the gap size between the propellant grain and the case and the vibration frequency on the mechanical response of the grain were studied. This shows that with a constant vibration frequency, the stress of the grain increases first and then decreases with increasing gap size. Moreover, the stress increases with increasing vibration loads.

Experimental investigation on the effect of axial gap on performance and unsteady pressure pulsations of low head axial flow hydraulic turbine

The stable operation of axial flow turbines (AFTs) in the energy conversion process directly affects their safety and performance. Because of its unstable pressure features, a dynamic analysis of its internal flow characteristics is required. To analyze, evaluate, and compare the pressure variation within the turbine under the base gap (Ƣ = 0.05D) and different axial gaps (Ƣ) of 0.09D, 0.14D, and 0.18D, a reliable measurement approach is required. Pressure sensors were installed on the flow domain of the AFT to measure dynamic pressure pulsation under various Ƣ and running flow conditions. Based on the experimental result, a 28% and 2.8% increase in turbine efficiency was recorded when the Ƣ was increased from 0.05D to 0.09D at 0.8Qd (design flow rate) and 1.0Qd, respectively.Further analysis of the frequency spectra reveals different unsteadiness in the flow structures due to changes in Ƣ which resulted in various excitation signals. A decrease in the Ƣ leads to an increase in pressure pulsation intensity. Consequently, AFT with Ƣ of 0.09D was recommended since it provides maximum efficiency with fewer pulses compared with Ƣ = 0.05D, where the vibrations are at peak value. The findings above will aid in the optimum use of energy resources since energy generated from AFT is clean and free of pollution and can lead to a sustainable energy generation process.

Experimental Investigation on the Effect of Axial Gap on Performance and Unsteady Pressure Pulsations of Low Head Axial Flow Hydraulic Turbine

Experimental Investigation on the Effect of Axial Gap on Performance and Unsteady Pressure Pulsations of Low Head Axial Flow Hydraulic Turbine

The Effect of Gapping on Compressor Performance

Abstract In this paper, we study the effect of rotor-stator axial gap on midspan compressor loss using high-fidelity scale-resolving simulations. For this purpose, we mimic the multi-stage environment using a new numerical method that recycles wake unsteadiness from a single blade passage back into the inlet of the computational domain. As a result, a type of repeating-passage simulation is obtained such as observed by an embedded blade-row. We find that freestream turbulence levels rise significantly as the size of the rotor-stator axial gap is reduced. This is because of the effect of axial gap on turbulence production, which becomes amplified at smaller axial gaps and drives increases in dissipation and loss. This effect is found to raise loss by between 5.5% and 9.5% over the range of conditions tested here. This effect significantly outweighs the beneficial effects of wake recovery on loss.

Effects of axial gap and nozzle distribution on aerodynamic forces of a supersonic partial-admission turbine

The turbine in an LH2/LOX rocket engine is designed as a two-stage supersonic partial-admission turbine. Three-dimensional steady and unsteady simulations were conducted to analyze turbine performance and aerodynamic forces on rotor blades. Different configurations were employed to investigate the effects of the axial gap and nozzle distribution on the predicted performance and aerodynamic forces. Rotor blades experience unsteady aerodynamic forces because of the partial admission. Aerodynamic forces show periodicity in the admission region, and are close to zero after leaving the admission region. The unsteady forces in frequency domain indicate that components exist in a wide frequency region, and the admission passing frequency is dominant. Those multiples of the rotational frequency which are multiples of the nozzle number in a full-admission turbine are notable components. Results show that the turbine efficiency decreases as the axial gap between nozzles and the 1st stage rotor (rotor 1) increases. Fluctuation of the circumferential aerodynamic force on rotor 1 blades decreases with the axial gap increasing. The turbine efficiency decreases as the circumferential spacing between nozzles increases. Fluctuations of the circumferential and axial aerodynamic forces increase as the circumferential spacing increases. As for the non-equidistant nozzle distribution, it produces similar turbine performance and amplitude-frequency characteristics of forces to those of the normal configuration, when the mean spacing is equal to that of the normal case.

Effects of axial gap on aerodynamic force and response of shrouded and unshrouded blade

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.

Effect of Axial Gap between Diffuser Inlet and Impeller on Efficiency and Flow Pattern of Centrifugal Fans

Inlet is one of the basic elements of squirrel cage fan that can have great effect on performance and losses, especially between inlet exit and first section of impeller width. In this paper the effect of axial gap between inlet diffuser and impeller on performance and flow pattern is considered. Three diffuser inlet sizes with respect to impeller size (smaller, nearly same and bigger than inner impeller diameter) and three axial gaps within the available dimensions of the casing and impeller were chosen. Numerical simulations were performed to find the effect of this axial gap on flow pattern, performance and efficiency. From the simulation of each case study, flow pattern and its mechanism and the causes that affecting the efficiency and performance due to axial gap are analyzed and presented.

Effect of axial gap between inlet nozzle and impeller on efficiency and flow pattern in centrifugal fans, numerical and experimental analysis

Inlet is one of the basic elements of squirrel cage fan that can have great effect on performance and losses, especially between inlet nozzle exit and first section of impeller width. But, enough research has not been done on its parameters. In this paper the effect of axial gap between inlet nozzle and impeller on performance and flow pattern is considered. Four inlet nozzle sizes with respect to impeller size (two smaller, nearly same and bigger than inner impeller diameter) and three axial gaps within the physical dimensions of the casing and impeller were chosen. Numerical simulations with different turbulence models, special geometry and mesh pattern were performed to find the effect of this axial gap on flow pattern, performance and efficiency. For the validation of numerical results, some experiments were done and all the performance parameters were compared with that of numerical simulations. These results show good matching between experimental and numerical results. From the simulation of each case study, flow pattern and its mechanism and the causes affecting the efficiency and performance due to axial gap are analyzed and presented.

Effects of Axial Gap on the Vane-Rotor Interaction in a Low Aspect Ratio Turbine Stage

An extensive experimental analysis on the subject of unsteady flows in a low aspect-ratio turbine stage was performed at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. Three different vane-rotor axial gaps were considered ranging from 16 to 50% of the stator axial chord. Steady flow measurements at different axial planes in the stator-rotor gap were carried out to provide a complete description of the three-dimensional flowfield entering the rotor for different axial gaps. The blade row interaction and its dependence on the axial gap were evaluated by means of phase-resolved aerodynamic measurements downstream of the rotor. Unsteady numerical simulations were also performed to support the interpretation of the experiments. Results show a strong dependence of the time-averaged and phase-resolved flowfield on the stator-rotor spacing. The blade row interaction is mainly driven by the vortex-blade interaction in the hub region, and by the rotor incidence unsteadiness produced by the stator flow structures. Different interaction phenomena take place for the different axial gaps, depending on the magnitude of the stator vortices and on the superposition between the stator wake and potential field. On the contrary, the tip region is dominated by the rotor aerodynamics, which are found to be almost steady in the relative frame. Spanwise efficiency profiles evidence the different effects related to the single blade row as well as to the wake and vortex interactions on the performance. The maximum overall efficiency and the minimum unsteadiness are achieved for a vane-rotor axial gap equal to one third of the stator axial chord, or five sixths of the stator throat.

Effects of Axial Gap on Unsteady Secondary Flow in One-Stage Axial Turbine

Effects of Axial Gap on Unsteady Secondary Flow in One-Stage Axial Turbine