Showing 40 results for Stall
Volume 2, Issue 1 (7-2021)
Abstract
Urbanization and population growth in metropolitan areas, on the one hand, and the growth of large-scale industrial activities, on the other hand, have led to changes in the climate of urban areas.This research is based on the classification of types of research in the category of descriptive and explanatory studies. Based on the results in the category of applied studies. It is based on qualitative and quantitative research processes. The research method is a combination of descriptive-analytical methods and software simulation with software Envi-Met software. Data is quantitative and qualitative related to the quality of space. Implementing it includes conceptual and theoretical modeling, software modeling, change in the type and amount of variables and testing the software model to find optimal answers. For this purpose, a basic model based on common urban forms in Tehran is selected and in which indicators such as the location of building blocks, orientation, the distance between blocks, the height of blocks in Envi-Met software are modeled and based on the index of thermal comfort and degree. PMV temperature was evaluated. According to the software outputs, it can be concluded that the location, distance, orientation and height have a positive effect on reducing thermal islands and providing thermal comfort conditions
Volume 4, Issue 1 (6-2020)
Abstract
Research subject: The use of nanoparticles, especially nano-antibiotics, increases their efficacy. More uniform release of antibiotics is one of the benefits of being nano. They can also be made using ointment or banderol to absorb through the skin to the infection, thereby reducing its side effects. Amoxicillin is one of the most widely used antibiotics in the world which can be prevented by increasing the use of other strong antibiotics if promoted as nanoparticles. Determining the mechanism of nanoparticle formation of this drug is an important factor for its commercial production.
Research approach: The purpose of this study was to determine the nucleation mechanism and time of induction of crystallization of amoxicillin nanoparticles in the presence of surface active agents ‘CTAB’ and ‘SDS’. Therefore, the effect of amoxicillin concentration and stabilizing concentration on the crystallization process was investigated. In this project, a combination of inductive-reactive crystallization was used. In this method, amoxicillin sodium was produced with sodium hydroxide, amoxicillin sodium, has a much higher solubility in water. Then, by adding hydrochloric acid, amoxicillin will be recovered and supersaturated. SEM and DLS analyzes were used to determine the properties of amoxicillin nanoparticles. All the experiments were repeated twice.
Main results: The results show that particles with a mean size of 50 nm were formed, and the particle stability was confirmed up to one week after formation. The results of the experiments show that the nucleation mechanism is the primary type with an average explanatory factor (R2) equal to 0.9887 and adding a stabilizing agent has no effect on the nucleation mechanism.
Volume 4, Issue 1 (6-2020)
Abstract
Abstract
Research Subject: In recent years, the use of graphene nanoplatelets (GnPs) in polymer nanocomposites has attracted considerable attention. Dispersion state of GnPs in the polymer matrix has a great importance which can affect microstructure and final properties of nanocomposite. Therefore, in the present work, the effect of compatibilizer on the dispersion state of GnPs and also on internal structure, orientation, and tensile properties of polypropylene (PP)/GnPs nanocomposite fibers are investigated.
Research Approach: PP/GnPs nanocomposite fibers containing 0.1% and 0.5% GnPs with and without maleic anhydride-grafted polypropylene (PP-g-MA) were melt spun. Dispersion state and location of GnPs in the nanocomposite fibers were investigated by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Fiber orientation and crystallinity were studied by polarized Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC), respectively. Moreover, fracture behaviour of PP/GnPs nanocomposite fibers was investigated by cross-sectional scanning electron microscopy (SEM) images of tensile fractured samples. Using Halpin-Tsai model, experimental tensile moduli of fibers were compared with the predicted values.
Main Results: TEM images show that in the compatibilized PP/MA/GnPs nanocomposite fibers, GnPs aggregates decrease and their size also reduces, suggesting that GnPs dispersion improved. An increase in Lp of the compatibilized sample recorded from SAXS analysis indicates that the more GnPs are located in the intrafibrillar region. Based on polarized FTIR and DSC results, orientation and crystallinity of PP/G0.5 nanocomposite fiber are found to significantly increase after inclusion of PP-g-MA. Moreover, reinforcing effect of GnPs in PP/MA/GnPs nanocomposite fibers could be explained by better GnPs dispersion and changes in internal structure of fiber. Furthermore, the tensile fracture behavior of PP/GnPs nanocomposite fiber changes from ductile to brittle in the presence of PP-g-MA.
Volume 6, Issue 1 (6-2022)
Abstract
Oil extracted from the underground oil reservoirs contains heavy hydrocarbons.Heavy hydrocarbons include waxes,asphalts and resins that can appear as solids in compounds,which waxes are of particular importance.Changes in factors such as temperature,pressure,compounds of light components in petroleum compounds,etc.Cause the formation of solid paraffin wax deposits in these compounds.The wax precipitate formed mainly contains paraffins,naphthenes and to a lesser extent aromatics.The formation of these sediments in the first stage can block the underground pores, reduce their permeability and reduce the efficiency of oil extraction.In the next stages,the formation of deposits will lead to many problems. For example,it can clog pipes and increase flow resistance, resulting in a drop in flow pressure and,in addition to increasing the power required to pump fluid, cause premature depreciation of the facility.The issue of wax sediment formation and the factors affecting it have been discussed by researchers for many years and different methods have been studied to control it.In this project,by examining 1 nanoparticle of SiO2,as chemical inhibitor, acceptable results were obtained in reducing the wax appearance temperature(WAT).First,using differential scanning calorimetry analysis,a temperature of 250C was obtained for the crude oil cloud point.Then,by adding nanoparticles in different concentrations,this temperature was significantly reduced for different amounts of nanoparticles.Analysis of polarized optical microscopy also shows the change in structure of wax crystals to a disk like after the addition of nanoparticles. To investigate the flow behavior of crude oil,the apparent viscosity parameter was used at shear rates of 0.01,0.1 and 1 rpm and higher and lower temperatures of WAT temperature.Then,using wax deposition of oil samples by two analyzes of X-ray diffraction(XRD) and scanning electron microscopy(FESEM) with EDAX additive to study the dispersion of nanoparticles in wax deposits and changes resulting from the addition of nanoparticles in depositions was paid.In this regard,according to X-ray diffraction analysis,it was found that the nanoparticles had no chemical interaction with wax molecules,but was a confirmation of the results obtained in the analysis of differential scanning calorimetric analysis.The layered structure of the wax precipitate by adding nanoparticles to a fine-grained structure was also one of the results of scanning electron microscopy analysis.
Volume 11, Issue 2 (6-2020)
Abstract
α-crystallin is a member of small heat shock protein family (sHSP) which shows both structural and chaperone functions. This protein plays important role in eye lens transparency and indicates protective function in the other tissues. The lenticular levels of copper ions significantly enhance in diabetic patients, aged and cataractous lenses. In eye lenses, the free copper ions induce ascorbic acid auto-oxidation, leading to formation of dehydroascorbic acid and other oxidative products as well as reactive oxygen species. The oxidized forms of ascorbic acid along with the reducing sugars enter into pathological reactions with the eye lens proteins, forming toxic advanced glycation end-products (AGEs). As one of the main components of eye lens antioxidant defense mechanism, glutathione could scavenge the copper ions, inhibiting the formation of reactive oxygen species in eye lenses.
In the current study, the structural and functional properties of human αB-crystallin were assessed using different spectroscopic methods. In the presence of copper ions, αB-crystallin exhibited important alterations in both structure and chaperone activity which upturned in the presence of glutathione. Moreover, incubation of human αB-crystallin with copper resulted in significant increase in the protein oligomeric size distribution which largely prevented upon simultaneous incubation with glutathione.
Overall, glutathione may scavenge free copper ions in the lenticular tissue, inhibiting their damaging effects on crystallin proteins and other redox-sensitive molecular targets such as ascorbic acid. Our results may introduce a new protective role for glutathione which is highly important in diabetic and aged lenses showing increased levels of copper ions.
Volume 12, Issue 1 (4-2012)
Abstract
Surge and rotating stall phenomena are two dynamic instabilities that occur in both axial and centrifugal compressors. Surge is the stream instability phenomenon in compressor that imposes severe damages to the compressors. Nowadays, suppressing surge phenomenon is one of the most important issues in oil and gas industries, especially when flow reduction or gas reflux is considered. This research seeks to extract the required technical information about control lines, surge lines, and to present a new combined method to determine the performance curve of 6 rows of gas compressors in Asmari Kupal gas pressure boost station (National Iranian South Oil Company) made in Germany by MAN BORSIG Company, and to design a smart controller in order to increase the reliability of the control system and improve the machine performance. Finally, the system performance validity is shown by simulating a surge characteristic curve and implementing two points of the compressor operation condition
Atefeh Salmasi, Abdollah Shadaram, , ,
Volume 12, Issue 6 (3-2013)
Abstract
Plasma actuator is one of the newest devices in flow control techniques which can delay separation by inducing external momentum to the boundary layer of the flow. The purpose of this paper is to simulate a NLF0414 airfoil both experimentally and numerically in presence of the body force vector induced by a specific plasma actuator. For this reason, the simulation is done both numerically and experimentally for a NLF0414 airfoil with the compressible 25 m/s velocity airflow in two different cases: with no plasma actuator located on the airfoil and with body force produced by a plasma actuator located on the top of the airfoil in order to investigate the effect of plasma on the flow passing over it. The results showed that presence of a plasma actuator on the top surface of the airfoil, close to the separation point, transferred the separation point from x=16 mm to x=41 mm at the angle of attack of 18 degrees. This separation delay caused a 35% increase in the ratio of lift to drag coefficient or the efficiency of the airfoil in the same angle of attack.
Volume 13, Issue 6 (11-2011)
Abstract
Carbon and sulfur isotopic data are helpful in understanding environmental conditions under which soils are formed. Soils from 18 sampling sites along a climotoposequence from higher Laleh Zar Mountains (4,351 m above sea level with xeric-mesic soil moisture-temperature regimes) to Shahdad depression (250 m above sea level with arid-hyperthermic soil moisture-temperature regimes) in Kerman Province, central Iran, were studied. δ 13C values of the soil organic carbon varied between -20.6 ‰ and -26.9 ‰ PDB. δ 13C values of pedogenic carbonates varied between -2.2 ‰ and +2.2 ‰ PDB and a decreasing trend was observed downward in the climotoposequence. A positive correlation (r= 0.6) was found between δ 13C and δ 18O values in the lower arid landscape, but a different relationship (r= 0.37) in the upper Mediterranean climatic positions was observed. It seems that the presence of more C3 plants under stress and more decomposition of organic matter in lower positions of the landscape has taken place. δ 13C values of soil organic carbon and pedogenic carbonates and their trend along the gradient showed that higher proportion of C3 plants at lower elevations and presence of more C4 plants in the past history of upper landscape positions may have been experienced. Mean δ34S value of 11.3‰ showed that lower Cretaceous sea sulfate may have been the source of sulfur in the area. Mean δ D and δ 18O values of -51.2‰ and +6.0‰ in gypsum crystallization water showed that direct deposition from a solution saturated with gypsum is the only probable mechanism of gypsum formation in the area.
Mostafa Nakhaei, Sayyed Hashemi,
Volume 13, Issue 14 (3-2014)
Abstract
In this research, the hot deformation behavior of API X70 steel was investigated by hot compression tests. A temperature range between 950 and 1150 °C was used for experiments with different strain rates of 0.01, 0.1 and 1 s-1. The work hardening rate versus stress curves were used to reveal if dynamic recrystallization (DRX) occurred. The application of constitutive equations to determine the hot working constants for the tested steel was discussed. Using regression analysis, the stress multiplier (α), the apparent stress exponent (n), and the activation energy (Qd) for DRX were calculated as 0.016 and 4.420, and 382 kJ/mol, respectively. Furthermore, the effect of Zener–Hollomon parameter (Z) on the characteristic points of flow curves was investigated using the obtained relations. The dynamic recrystallization (DRX) kinetics of API X70 steel was also studied and its governing equation was derived.
Reza Taghavi Zenouz, Ehsan Solki, Hadi Afshari,
Volume 14, Issue 3 (6-2014)
Abstract
In this article, one of the new casing treatment methods for improving of compressor performance have been investigated. Stepped tip gap is one of the appropriate methods of casing treatment that its functionality in axial compressors have been proved lately. In the present study, for the first time, effects of stepped tip gap on stall margin improvement of a centrifugal compressor have been evaluated numerically. Simulation has been done using Fluent software and k-ε turbulence modeling. To find the optimum geometry of stepped tip gap, seven casing geometries with one untreated smooth wall were considered. Results of velocity contours and streamlines patterns on various azimuthal and meridional planes showed that by using casing with stepped tip gap, tip leakage flow has been weaken and flow blockage in compressor main passage has been reduced. Hence, stepped tip gap extends the stable operating range of compressor and delays the occurrence of stall phenomenon. Results of present research, shows that by using stepped tip gap with optimum size, stall margin of the proposed compressor was improved by 7.38%.
Masoud Rakhsh Khorshid, Sayyed Hojjat Hashemi, Hossein Monajati,
Volume 14, Issue 13 (3-2015)
Abstract
Thermo-mechanical control processing is used to produce API pipeline steels. To design a proper thermo-mechanical cycle, it is needed to determine the critical temperatures including non-recrystallization temperature (Tnr) and austenite to ferrite transformation start and finish temperatures (Ar3 and Ar1). In this research, average schedule and continuous cooling torsion after a real schedule were used to determine critical temperatures of API X65 steel for the first time in Iran. This steel is imported from abroad and is extensively used in Iran for large diameter, high-pressure gas transportation pipelines and for oil transmission networks. It was found that the average schedule was a proper method to determine Tnr; while, continuous cooling torsion was proper to determine Ar3 and Ar1. The obtained results were compared with Boratto and Ouchi experimental relations with the purpose of evaluating the reliability of these relations for determination of Tnr and Ar3 critical temperatures. The obtained 4 percent relative error from both relations showed the need of conducting the experimental studies. With regard to the lack of experimental data, the obtained results can be used to design the optimum thermo-mechanical control process through the selection of proper temperature ranges for rough and finish rolling stages in domestic manufacturing of the test steel.
Hamed Fatemi, Alireza Riasi, Seyyed Ahmad Nourbakhsh,
Volume 14, Issue 13 (3-2015)
Abstract
Nowadays, using renewable energies, specifically ocean wave energy, is of importance in the world. One of the methods by which this energy can be harnessed is through using axial turbines with low head. In this study, performance of an axial turbine ocean wave of Wells type installed on the floating oscillating platform has been numerically studied. The length of the oscillating bed is equal to the wave length of the ocean upon its center the Wells turbine has been installed. This design causes the inlet flow rate to be doubled, which will in turn increase the power. In this way, the governing equations include continuity and momentum equations have been solved considering SST turbulence model. Furthermore, the acquired results have been verified through mesh independency analysis and have been validated by comparison with the available experimental data. The results show that with decreasing the clearance and setting it to 2% of the chord length value, the maximum efficiency, which is approximately 35%, will be gained. Moreover, by varying the angles from 0 to 12° with respect to its tip, achieve higher efficiency in different velocity ratios. On the other hand, employing a blade with variable profile will lead to postponing stall phenomena. Moreover, employing multistage turbines with guide vanes at the mid stage can improve efficiency by 9 percent.
Volume 14, Issue 63 (6-2016)
Abstract
Using nutritionally valuable products is important as people taste is going toward varies foods. The use of pumpkin can provide nutritionally qualified and valuable product, diversity of products and higher customer choice because it contains helpful and therapeutic compounds. In the current research, different levels of modified starch (0.2, 0.15, 0.1 percentage) and micro-crystalline cellulose (1.5, 1, 0.5 percentage) were used in the production of fruit butter for improving the consistency and the texture properties including hardness, toughness, gummy, cohesiveness, chewiness,…. and color attributes including three factors of L, a and b were evaluated. The results showed that the cohesiveness, gummy and hardness decreased with increasing the micro-crystalline cellulose. Furthermore, with increasing the modified starch increased the hardness, toughness, cohesiveness, chewiness, L and b parameters, but it had no effect on gummy, significantly. The pumpkin can be used as a natural and also enrichment combination in the process of the productions such as fruit butter due to its functional properties.
Seyed Erfan Salimipour, Shima Yazdani,
Volume 15, Issue 6 (8-2015)
Abstract
In the present paper, a two dimensional numerical analysis of the dynamic stall phenomenon associated with unsteady flow around the NACA 0012 airfoil at low Reynolds number (Re ≈ 130000) is studied. For this purpose, a thin blade with height of 0.005 chord length was placed vertically on the airfoil to control the bursting of the laminar leading edge separation bubble. The numerical simulation of flow is based on discretization of convective flaxes of the turbulent unsteady Navier-stokes equations by second-order Roe’s scheme and an explicit finite volume method in a moving coordinate system. Because of the importance of the time dependent parameters in the solution, the second-order time accurate is applied by dual time stepping approach. Three oscillating patterns with different frequencies and angular amplitudes were used to study the dynamic stall phenomenon. In order to validate the operation of computer code, some results for static and dynamic stall are compared with experimental data. The results of this study showed that the burst control blade had the acceptable effects on the dynamic stall control; so that these effects were increased while the oscillation frequency was raised. The best result occurs in 5 deg angular amplitude and reduced frequency of 0.15; so that the lift stall reduced 50% and there was not any obvious stall in drag coefficient.
Volume 15, Issue 85 (3-2019)
Abstract
Green tea leaves is a non-fermented product which contains many phenolic compounds. Green tea polyphenols are natural compound with antioxidants and anti-carcinogenic potential. Polyphenols are sensitive to high temperature and alkaline pH. To improve the stability of polyphenols, green tea extract was microencapsulated by co-crystallization technique. Entrapment yield, loading capacity, antioxidant activity, characteristics of co-crystallized product such as moisture, water activity, bulk and tapped density, solubility and hygroscopicity, morphology as well as flowability properties of powder (carr index, hausner ratio and angle of repose) were characterized. It was revealed that the effect of concentration on total phenolic compounds of co-crystallized products was significant (p<0.05). Encapsulation efficiency was increased by increasing the extract concentration. The 10% concentration of microencapsulated extract showed the highest DPPH scavenging activity, ABTS and hydroxyl radicals inhibition activity, and reducing power (56.90, 69.37, 71.63% & 0.81, respectively). The difference in particle size of co-crystallized product was significantly (p˂0.05) influenced the flow properties. In general, the values of water activity, moisture content and hygroscopicity showed that co-crystallized product was stable and have good characteristics during storage. Therefore, microencapsulation by co-crystallization technique can be used as an efficient method for increasing the stability of green tea extract against the environmental conditions.
Reza Taghavi, Mohammad Hossein Ababaf Behbahani, Ali Khoshnejad,
Volume 16, Issue 7 (9-2016)
Abstract
Rotating stall alleviation in an axial compressor with deployment of air injection at its rotor blade row tip region has been experimentally investigated. Twelve air injectors had been mounted evenly spaced around the compressor casing upstream the rotor blade row. Initially, improvement of the compressor overall performance has been examined through air injection, especially at stall point condition. Instantaneous flow velocities at various radial and circumferential positions were measured simultaneously utilizing hot wire anemometry. These unsteady results, obtained from these latter measurements together with signal frequency analyses, provided to describe the stall inception process and consequent flow induced fluctuations and also alleviation process of stall during the air injection. Results show that a small amount of air injection at the rotor blade tip region can affect the total pressure rise and specifically can increase the compressor stall margin efficiently. Air injection of less than 1% of the compressor main flow rate through the injectors has caused the stall margin to be improved by 9%. Air injection at the blade row tip has caused its beneficial effects to extend throughout the blade whole span, especially while working at the near stall conditions.
Abbas Ebrahimi, Mahmood Sekandari,
Volume 16, Issue 8 (10-2016)
Abstract
Wind turbines are subject to various unsteady aerodynamic effects. This includes the wind gust and the change of wind direction. In this work, the aeroelastic behavior of a reference horizontal axis wind turbine has been investigated under different wind gusts and yaw conditions. Unsteady blade element momentum (UBEM) theory and Euler-Bernoulli beam assumption were used to rotor power estimations. To take into account the time delay in aerodynamic loads due to a sudden change in inflow conditions, a dynamic wake model was implemented. The ONERA dynamic stall model was coupled into the BEM theory to improve the aerodynamic loads prediction in the unsteady inflow and yaw conditions. To verify this method, the results in the case of steady-state are compared with the NREL 5 MW wind turbine and in the unsteady case are compared with the Tjaereborg test turbine. The results indicate that sudden change in wind speed causes sharp fluctuations in terms of elastic torsion of the blade and other parameters such as rotor power. Increasing in wind gradient can leads to increasing time delay to a new equilibrium. The increase in yaw angle can be contributed to the rotor power and the periodic loads reduction. The method presented here may facilitate improvements in the controller design for wind turbines.
Mahdi Jalalifar, Behzad Ghadiri, Saleh Fallah,
Volume 16, Issue 10 (1-2017)
Abstract
One of the important purposes of aero-engine high speed compressor design is to decrease its weight. In order to achieve this purpose, it is required to increase the capability of pressure producing in each individual stage of the compressor. The most common way is to use of high pressure aspect ratio blades. These long and thin blades are exposed to serious vibrations in the high speed flow because of the aeroelastic instability. Mechanical designers link adjacent blades by using Mid-span shroud (damper) to decrease the blade destructive vibrations. This dampers cause flow blockage and turbomachine performance loss. In the previous studies, less attention has been done on the effect of damper on blade shocks, trailing edge vortices and near stall condition. In this paper, aerodynamic performance of a compressor with and without mid-span damper has been investigated and compared. On the other hand, the damper effect on the formation and behavior of shock induced separation has been investigated in each two cases. As a result, presence of damper causes an isentropic efficiency reduction. This damper causes 33% pressure loss on the blades in the region of the extent of 2.7% of the blade span around damper. Turbulence due to the presence of damper leads to the distortion of the vortices pattern on training edge.
Shahrokh Shams, Mohammad Reza Kazemi, Babak Mirzavand Borojeni, Zahra Khojasteh Bakhtek Koupaie,
Volume 16, Issue 12 (2-2017)
Abstract
In this paper, by defining a new paradigm for nonlinear aerodynamic equations of flow separation and static stall, a new form of nonlinear aeroelastic equations for two degrees of freedom airfoils (torsional and bending) are presented. Structural equations are based on the nonlinear mass-spring model; include the nonlinear quadratic and cubic terms. Aerodynamic equations are obtained by combining the unsteady Wagner model and the nonlinear lift coefficient-angle of attack for simulating stall using a cubic approximation. Hamilton’s principle and Lagrange equations were used to derive the aeroelastic equations. The obtained integro-differential nonlinear aeroelastic equations are solved using a new time-history integration method. The aeroelastic behavior of the airfoil is compared in both unsteady and quasi-steady flow. Using the time-history method compared to the phase space method leads to fewer equations. The results show that the aeroelastic behavior of airfoil with a linear structure, using a nonlinear aerodynamic theory for the stall, causes oscillations with a limit cycle in unsteady and quasi-steady flow compared to other linear aerodynamic theories. Also, the use of the cubic curve instead of the piecewise linear curves which is commonly used in other references, although, causes an apparent complication of the equations, reduces the computational time due to faster convergence in solution and makes the reduction in errors. The results show that the use of nonlinear aerodynamic static stall not only reduces the instability velocity, but also reduces the amplitude of limit cycle oscillations in both unsteady and quasi-steady regimes.
Nozar Akbari,
Volume 17, Issue 1 (3-2017)
Abstract
Inlet distortion that may be occurred for various reasons at the entrance of a gas turbine, it is caused to disturbed in compressor performance conditions and also all engine components, so it is very important to investigate its controlling methods. The aim of this paper is numerical simulation of inlet distortion in an axial compressor rotor and active control of the instabilities by the air injection at the blade tip region. Flow simulation of inlet distortion is accomplished at compressor entry with five different geometries of circumferential blockage (amounts of circumferential blockage are: 5%, 10%, 15%, 20% and 25% of the compressor inlet duct). For active control of instabilities, 12 injectors have been mounted upstream of the rotor blade row that distributed in circumferential directions symmetrically. The injection mass flow rate does not exceed 2% of the compressor main flow rate at the design point. ANSYS CFX was used for simulation and the turbulence model of k-ω SST has been used through the calculations. The results show that increasing inlet distortion cause to decrease performance and rotor efficiency. Furthermore, for this rotor modeling condition, in 5% and 10% blockage, air injection can improve the rotor performance, but for more than 10% blockage, a strong wake region is formed after the distortion screen and air injection can cause negative effects on rotor performance. Because the strong instabilities can adversely affect the injectors flow and this method instead of modifying the flow field, make it more non uniform than before.
