Papers by mohammad mojaddam
Experimental study of the effect of the duct on dual co-axial horizontal axis wind turbines and the effect of rotors diameter ratio and distance on increasing power coefficient
Energy
Droplet generation in a co-flowing microchannel influenced by magnetic fields applied in parallel and perpendicular to flow directions
Journal of Magnetism and Magnetic Materials
In this study, ferrofluid droplet generation in a co-flowing microchannel is numerically studied ... more In this study, ferrofluid droplet generation in a co-flowing microchannel is numerically studied in the presence of a uniform magnetic field, exerted parallel or perpendicular to the flow direction. The effects of field direction and parameters like the magnetic Bond number and two-phase flow rate ratio on the droplet breakup formation characteristics are investigated. Depending on the field direction, different responses of the system to alterations in the mentioned parameters are observed. By increasing the magnetic Bond number, droplet dimensionless diameter and dimensionless velocity increases for the parallel magnetic field and decreased by 5.15% and 36.91% for the vertical field, respectively. Implementing the perpendicular field, the droplet formation properties become insensitive to the magnetic Bond number at values more than 4.24 due to the transformation of the flow pattern from dripping to the slug flow regime. By increasing the two-phase flow rate ratio, the dimensionless diameter of the droplets decreases while their dimensionless velocity increases.
Experimental and numerical investigations of radial flow compressor component losses
Journal of Mechanical Science and Technology, 2014
This research numerically and experimentally investigates a small turbocharger radial flow compre... more This research numerically and experimentally investigates a small turbocharger radial flow compressor with a vane-less diffuser and volute. The geometry of the compressor is obtained via component scanning, through which a 3D model is prepared. The flow inside this model is numerically analyzed by using a Navier-Stokes solver with a shear-stress transport turbulence model. The characteristic curves of the compressor and the contributions of its components to total pressure drop are acquired by measuring the static and total pressures at different cross sections of the compressor. Numerical results are verified with the experimental test results. The model results exhibit good agreement with the experimental results. In particular, the results show that the losses related to the impeller are higher than those related to the stationary components at different conditions, with the former causing a decline of at least 15% in compressor isentropic efficiency. The contribution of stationa...
Performance Improvement of Supercritical Co2 Power Cycles by Machine Learning Method
SSRN Electronic Journal
Evaluating the Effects of Temperature on Flow-By Capacitive Deionization
SSRN Electronic Journal
Numerical and Experimental Study of the Ducted Diffuser Effect on Improving the Aerodynamic Performance of a Micro Horizontal Axis Wind Turbine
SSRN Electronic Journal, 2021
Separation of blood cells has a widespread application in medical sciences. Separation of these c... more Separation of blood cells has a widespread application in medical sciences. Separation of these cells helps identifying their properties. Knowing the properties of circulating tumor cell’s (CTC) and the effect of different drugs on them can significantly help to develop and improve patient’s treatment methods. During recent years, microfluidic devices for separation and sorting of these cells have been significantly developed. There are different methods for cell sorting. In this research, the size and the electrical properties of cells have been considered as the main criteria for cell separation and by combining pinched flow fractionation (PFF) as a passive method with dielectrophoresis as an active method, the separation of MDA-435 mammalian circulating tumor cell from white and red blood cells is investigated. These cells have small size differences where in pinched flow fractionation, incapability to separate particles of similar sizes is a major challenge. In this research, di...
Investigating the Separation Bubble Behavior on the Suction Side of a High-Lift Low-Pressure Turbine Blade Using Proper Orthogonal Decomposition
Centrifugal Compressor Volute Design & Performance Optimization with Experimental Validation
Analytical and Bioanalytical Chemistry, 2021
Blood plasma separation from undiluted blood is an essential step in many diagnostic procedures. ... more Blood plasma separation from undiluted blood is an essential step in many diagnostic procedures. This study focuses on the numerical optimization of the microfluidic blood plasma separator (BPS) and experimental validation of the results to achieve portable blood plasma separation with high purity and reasonable yield. The proposed design has two parts: a microchannel for blood processing and a tank, below the aforementioned main channel, for plasma collection. The study uses 3D computational fluid dynamic analysis to investigate the optimal ratio of heights between the top microchannel and the tank and their geometry at various flow rates. Thereafter, the results are compared with the experimental findings of the fabricated devices. These results are put in contrast with some recent reported works to verify the proposed device's contribution to the improvement of quality and quantity of the extracted plasma. The optimized design is capable to achieve a 19% yield with a purity of 77.1% and depending on the requirement of the point-of-care (POC) application. These amounts could be tuned for instance to 100% pure plasma, but the yield would decrease to 9%. In this study the candidate application is hemostasis, therefore, the BPS is integrated to a biomimetic surface for hemostasis evaluation near the patients.
International Journal of Heat and Fluid Flow, 2020
This paper investigates the vortex dynamics in the suction-side boundary layer on an aero-engine ... more This paper investigates the vortex dynamics in the suction-side boundary layer on an aero-engine low pressure turbine blade at two different Reynolds numbers at which short and long laminar separation bubbles occur. Different vortical patterns are observed and investigated through large eddy simulation (LES). The results show that at the higher Reynolds number, streamwise streaks exist upstream of separation line. These streaks initiate spanwise undulation in the form of vortex tubes, which roll-up and shed from the shear layer due to the Kelvin-Helmholtz instability. The vortex tubes alternately pair together and eventually distort and break down to small-scale turbulence structures near the mean reattachment location and convect into a fully turbulent boundary layer. At the lower Reynolds number, streamwise streaks are strong and the separated flow is unable to reattach to the blade surface immediately after transition to turbulence. Therefore, bursting of short bubbles into long bubbles can occur, and vortex tubes have larger diameters and cover a part of the blade span. In this case vortex pairing does not occur and vortex shedding process is promoted mainly by flapping phenomenon. Moreover, the results of dynamic mode decomposition (DMD) analysis show a breathing motion as a source of unsteadiness in the separation location, which is accompanied by the flapping phenomenon.
Journal of Applied Fluid Mechanics, 2020
Centrifugal pumps are among the most applicable machines in a wide variety of industrial systems ... more Centrifugal pumps are among the most applicable machines in a wide variety of industrial systems for fluid pumping and transportation. Therefore their optimization has always been of great importance. Pump impellers play an important role in these machines as the energy transfer takes place in this part. In the present study, the impeller of a centrifugal pump is optimized by investigating the effect of adding splitter blades and modifying their geometry. A centrifugal pump is experimentally tested and numerically simulated and the characteristic curves are obtained. In the first stage, two different sets of splitter blades with different lengths are added to the impeller and the effect of splitter blade lengths on the results are explored. The case with the highest total head and overall efficiency is selected for the optimization process. The main blade and the splitter blade leading edge position and also the splitter blade distance between two successive blades are selected for the optimization process in the second stage. Efficiency and total head of the pump are considered as the optimization objectives. Using Design of Experiment (DoE) technique, the design space is created and response surface method is utilized to find the optimum geometry. The results show adding splitters can improve total head by about 10.6% and by modifying the geometry using DoE technique it could increase further by 4.4% with the negligible effect on the pump overall efficiency.
Aerospace Science and Technology, 2019
The flow-field inside a gas turbine engine, especially in the low-pressure turbine, is very compl... more The flow-field inside a gas turbine engine, especially in the low-pressure turbine, is very complicated as it is normally accompanied by unsteady flow structures, strong and rapidly changing pressure gradients, intermittent transition of boundary layer, and flow separation and reattachment, especially during off-design performance. In this article, flow separation and reattachment on the suction side of an ultra-high-lift low-pressure turbine blade is studied and characterized using 3D Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. For turbulence modeling, transitional-SST method (γ-Re θ) is adopted. The simulations are performed at the exit Reynolds numbers of 200,000 and 60,000, and at a constant isentropic exit Mach number of 0.4. The shape and extent of the separation bubble are primarily dependent on large vortical structures due to the Kelvin-Helmholtz instability and spanwise vortex tube shedding. Therefore, a better prediction of these phenomena could result in a more realistic separation bubble identification and consequently more accurate profile loss assessment. In order to better capture the transitional flow characteristics, which are not often readily available from conventional computational fluid dynamics simulations, the method of Proper Orthogonal Decomposition (POD) is used in this study. Non-coherent structures in the main flow, such as separation bubble, are investigated and studied. The POD modes of pressure-field are analyzed to clarify the generation of spanwise vortex tubes after separation point. In the higher Reynolds number, low-energy small-scale structures in the separation zone and downstream of the trailing edge are observed from the POD analysis. In the lower Reynolds number, high-energy large-scale structures shed from the separated shear layer are identified, which are responsible for increasing turbulent kinetic energy as well as increasing profile losses. This study also shows that the combination of URANS and POD can successfully be used to identify the separation bubble.
Energies, 2019
The performance of an automotive turbocharger centrifugal compressor has been studied by developi... more The performance of an automotive turbocharger centrifugal compressor has been studied by developing a comprehensive one-dimensional (1D) code as verified through experimental results and a three-dimensional (3D) model. For 1D analysis, the fluid stream in compressor is modeled using governing gas dynamics equations and the loss mechanisms have been investigated and added to the numerical model. The objective is to develop and offer a 1D model, which considers all loss mechanisms, slip, blockage and also predicts the surge margin and choke conditions. The model captures all features from inlet duct through to volute discharge. Performance characteristics are obtained using preliminary geometry and the blade characteristics. A 3D numerical model was also created and a viscous solver used for investigating the compressor characteristics. The numerical model results show good agreement with experimental data through compressor pressure ratio and efficiency. The effect of the main compre...
Journal of Mechanical Science and Technology, 2017
An impeller design for radial flow compressors is addressed in several text books. According to p... more An impeller design for radial flow compressors is addressed in several text books. According to practiced methods, the overall dimensions and properties of an impeller can be determined using basic aerodynamic and thermodynamic relations. However, the values of several parameters and geometric details have not been strictly assigned. Hence, the experience and empirical relations of designers are important. The impeller meridional profile is an important detail that has a significant influence on the performance of the impeller. Generally, circular arc curves are implemented for this purpose. In this study, the effect of using elliptic curves is studied and compared with circular curves. An experimentally validated numerical code is used for this investigation. Two different compressors are studied to formulate the conclusion. Results show that elliptic curves can be a better initial choice for hub and shroud profiles compared with the commonly used circular arc. Smoother direction change with less secondary flow and related loss are identified as the improvement cause.
Applied Sciences, 2019
Centrifugal compressor performance is affected by many parameters, optimization of which can lead... more Centrifugal compressor performance is affected by many parameters, optimization of which can lead to superior designs. Recognizing the most important parameters affecting performance helps to reduce the optimization process cost. Of the compressor components, the impeller plays the most important role in compressor performance, hence the design parameters affecting this component were considered. A turbocharger centrifugal compressor with vaneless diffuser was studied and the parameters investigated included meridional geometry, rotor blade angle distribution and start location of the main blades and splitters. The diffuser shape was captured as part of the meridional geometry. Applying a novel approach to the problem, full factorial analysis was used to investigate the most effective parameters. The Response Surface Method was then implemented to construct the surrogate models and to recognize the best points over a design space created as based on the Box-Behnken methodology. The ...
Experimental Thermal and Fluid Science, 2016
Being able to optimal design and fabrication of compressors requires understanding of the flow st... more Being able to optimal design and fabrication of compressors requires understanding of the flow structure through the compressor components. Volutes are commonly the last main component in radial flow compressors. The stream passes through inlet, impeller and diffuser and finally is collected and discharged to the downstream pipeline by a volute. Volute shape has a direct and non-negligible effect on the compressor performance and its stable operating range. This component causes distorted pressure field in the upstream flow passages which could lead to the aero-mechanical forces acting on the impeller. As the flow inside the volute is fully three dimensional and turbulent, better understanding of flow mechanism has priority before modifying the volute design procedure. In this research the experimental and numerical flow investigation through a radial flow compressor volute are performed to recognize the flow structure. The whole compressor components including the inlet, impeller, vane-less diffuser and volute are modeled and the flow structure inside the volute is captured. The three dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with shear stress transport turbulence model. Flow field investigation through volute cross section is performed utilizing a five-hole probe. As the original volute is overhang type volute, the new external type volute is designed and fabricated based on the optimum design procedure. The results which are used for numerical model verification show that stage pressure ratio and total to total isentropic efficiency are increased by 2.5% and 1.9%, respectively at 70,000 rpm rotational speed using the new fabricated volute. The flow field inside the volute is also captured and compared to the experimental results obtained from the original volute setup and also for verifying the numerical model.
Investigation on Effect of Centrifugal Compressor Volute Cross-Section Shape on Performance and Flow Field
Volume 8: Turbomachinery, Parts A, B, and C, 2012
ABSTRACT In this article, the effects of volute cross section shape and centroid profile of a cen... more ABSTRACT In this article, the effects of volute cross section shape and centroid profile of a centrifugal compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by measuring rotor speed and flow parameters at the inlet and outlet of the centrifugal compressor. The three dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with SST turbulence model. The compressor characteristic curves were plotted. For model verification, the results were compared with experimental data, showing good agreement.Modification of a volute was performed by introducing a shape factor for volute cross section geometry. By varying this parameter, new volutes were generated and modeled. The effect of volute cross section shape on compressor pressure ratio and efficiency at design rotational speed were investigated. Also pressure non-uniformity around compressor impeller for new cases was calculated and reported.The results showed how the cross section shape of the volute can influence the compressor characteristics and the non-uniformity of circumferential static pressure as well.
Experimental and numerical investigations of radial flow compressor component losses
Journal of Mechanical Science and Technology, 2014
This research numerically and experimentally investigates a small turbocharger radial flow compre... more This research numerically and experimentally investigates a small turbocharger radial flow compressor with a vane-less diffuser and volute. The geometry of the compressor is obtained via component scanning, through which a 3D model is prepared. The flow inside this model is numerically analyzed by using a Navier-Stokes solver with a shear-stress transport turbulence model. The characteristic curves of the compressor and the contributions of its components to total pressure drop are acquired by measuring the static and total pressures at different cross sections of the compressor. Numerical results are verified with the experimental test results. The model results exhibit good agreement with the experimental results. In particular, the results show that the losses related to the impeller are higher than those related to the stationary components at different conditions, with the former causing a decline of at least 15% in compressor isentropic efficiency. The contribution of stationary components to efficiency decrease is approximately 4.8% at maximum efficiency mass flow rate and is limited to 7.1%. At low mass flow rates, the contribution of the diffuser to efficiency decline is higher than that of the volute. This finding is reversed at high mass flow rates. The performances of the diffuser and the volute are also studied by exploring total pressure and static pressure recovery coefficients, as well as the net radial force on the impeller shaft under a wide operating range.
Optimal Design of the Volute for a Turbocharger Radial Flow Compressor
Volume 2D: Turbomachinery, 2014
In this research, design methods of radial flow compressor volutes are reviewed; the main criteri... more In this research, design methods of radial flow compressor volutes are reviewed; the main criteria in volute primary designs are recognized and the most effective ones are selected. The effective parameters, i.e., spiral cross-section area, circumferential area distribution, exit cone, and tongue area of the compressor volute are parametrically studied to identify the optimum values. A numerical model has been prepared and verified through experimental data which are obtained from the designed turbocharger test rig. Different volutes are modeled and numerically evaluated using the same impeller and vane-less diffuser. For each model, the volute total pressure ratio, static pressure recovery and total pressure loss coefficients and the radial force on the impeller are calculated for different mass flow rates at design point and off-design conditions. The volute which shows better performance and causes lower the net radial force on the impeller at desired mass flow rates is selected as an optimal one. The results show the volute design approach differences at the design point and off-design conditions. Improving the pressure ratio and reducing total pressure loss at design point may result in the worse conditions at off-design conditions as well as increasing radial force on the impeller.
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Papers by mohammad mojaddam