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Optimization of a seven-stage centrifugal compressor by using a quasi-3D inverse design method
Mahdi Nili-Ahmadabadi,Farzad Poursadegh 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.11
This paper focuses on performance improvement of a centrifugal compressor. An inverse design method for 3D design approaches is formulated to address this concern. The design procedure encompasses two major steps. First, with the use of ball spine algorithm, which is an inverse design algorithm, on the meridional plane of impeller, the hub and shroud of impeller are computed based on a modified pressure distribution along them. Second, an original and progressive algorithm is developed for design of blade camber line profile on the blade-to-blade planes of impeller based on blade loading improvement. Full 3D analysis of the current and designed compressor is accomplished by using a Reynolds-averaged Navier–Stokes equations solver. A comparison between the analysis results of the current and designed compressor shows that the total-to-total isentropic efficiency and pressure ratio of the designed compressor under the same operating conditions are enhanced by more than 4.5% and 5%, respectively.
Centrifugal compressor shape modification using a proposed inverse design method
Mahdi Nili-Ahmadabadi,Farzad Poursadegh 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.3
This paper is concerned with a quasi-3D design method for the radial and axial diffusers of a centrifugal compressor on the meridional plane. The method integrates a novel inverse design algorithm, called ball-spine algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain, of which unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, unknown walls are composed of a set of virtual balls that move freely along specified directions called spines. The difference between target and current pressure distributions causes the flexible boundary to deform at each modification step. In validating the quasi-3D analysis code, a full 3D Navier-Stokes code is used to analyze the existing and designed compressors numerically. Comparison of the quasi-3D analysis results with full 3D analysis results shows viable agreement. The 3D numerical analysis of the current compressor shows a huge total pressure loss on the 90° bend between the radial and axial diffusers. Geometric modification of the meridional plane causes the efficiency to improve by about 10%.
Nili-Ahmadabadi, Mahdi,Nematollahi, Omid,Cho, Dae Seung,Kim, Kyung Chun Elsevier 2018 Applied thermal engineering Vol.137 No.-
<P><B>Abstract</B></P> <P>A real dense gas such as R245fa is mostly used in organic-Rankine-cycle turbine expanders. The dense gas effects should be taken into account, especially in the transonic and supersonic flow regimes. Oblique shock and the interaction of shock and separation on the turbine blades are phenomena that have little deviation between a real gas and an ideal gas. This research numerically simulated the flow passing through a cascade of simple straight blades with keen edges considered for an ideal gas (air) and dense R245fa gas in a supersonic flow regime. The blade geometry was selected so that the deviations between the dense and ideal gas flows would be clearer than that with actual blades. The AUSM density-based method and NIST real gas model were used to model the ideal and dense gas, respectively. A second-order scheme was used for discretization, and the shear stress transport (SST) model was for the turbulence. The results show that an oblique shock is created on the leading edge when the inlet Mach number is 2.18 in dense gas. In ideal gas, a bow shock is created at the front of the leading edge. Moreover, for a wall pressure coefficient distribution, the separation point in dense gas is posterior than that in ideal gas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flow passing through a cascade has numerically simulated. </LI> <LI> Simple straight blades with keen edges are considered. </LI> <LI> Ideal gas (air) and R245fa gas in a supersonic flow regime are compared. </LI> <LI> Oblique shock is created in dense gas while a bow shock is in ideal gas. </LI> </UL> </P>
Hadi Hoghooghi,Mahdi Nili-Ahmadabadi,Mojtaba Dehghan Manshadi 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.5
The goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. The nozzle is the main component of wind tunnels to create a uniform flow with minimal turbulence. Pressure distribution along nozzle walls directly affects the boundary layer thickness, pressure losses and non-uniformity of flow velocity through the test section. Although reduction of flow turbulences and non-uniformity through the test section can be carried out by nozzles with high contraction ratio, it increases the construction cost of the wind tunnel. For decreasing the construction cost of nozzle with constant test section size and mass flow rate, the contraction ratio and length of nozzle should be decreased; that causes the non-uniformity of outlet velocity to increase. In this study, first, three types of nozzle are numerically investigated to compare their performance. Then, Sargison nozzle with contraction ratio of 12.25 and length of 7 m is scaled down to decrease its weight and construction cost. Having scaled and changed to a nozzle with contraction ratio of 9 and length of 5 m, its numerical solution reveals that the non-uniformity of outlet velocity increases by 21%. By using the Ballspine inverse design method, the pressure distribution of the original Sargison nozzle is first scaled and set as the target pressure of the scaled down nozzle and geometry correction is done. Having reached the target nozzle, numerical solution of flow inside the optimized nozzle shows that the non-uniformity just increases by 5% in comparison with the original Sargison nozzle.
A Novel Approach for Energy Harvesting from Feedback Fluidic Oscillator
Masoud Alikhassi,Mahdi Nili-Ahmadabadi,Reza Tikani,Mohammad Hassan Karimi 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.4
Piezoelectric patches are widely used on a micro scale energy harvesting due to their simplicity and high flexibility. In this study a fluidic oscillator was used to effectively convert the kinetic energy of a fluid into the strain energy of the piezoelectric structure. The relationship between the input velocity and the frequency of fluid fluctuations in the fluidic oscillator was obtained and different positions for the piezoelectric beam and the effect of the input velocity on the output voltage was examined. The optimum electrical resistance was finally calculated for the maximum harvested power and the pressure drop caused by the fluidic oscillator and piezoelectric beam was investigated. The results indicated when the free end of the beam was inside the main chamber of oscillator, the beam fluctuates with its natural frequency so that the fluid oscillations frequency is close to the natural frequency at different velocity. However, when the free end of the beam was outside the main chamber, the voltage and power were maximized at the frequency of fluid oscillation equal to the natural frequency of the piezoelectric beam.