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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  

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Surge is one of the two destructive factors in compressors. surge is the stream instability phenomenon in compressor that imposes severe damages to the compressors. Nowadays, suppressingsurge phenomenon is one of the most important issues in oil and gas industries, especially when flow reduction or gas reflux is considered. According to Moore-Greitzer compressor model, this paper designs an active controller for surge control in constant speed centrifugal compressors. As such, the applied operator considered for surge control is Close Couple Valve (CCV) and it is designed to stabilize a centrifugal compressor system with disturbaces using nonlinear predictive controller. The proposed controller, without any information about the amount of Throttle Valve variations, could control the surge instability and reduce the distance between compressor operation point and the surge line. Finally, the compressor system with controller is simulated and the obtained results will show the efficiency of the designed nonlinear predictive controller

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In this research, the aerodynamic design of a centrifugal compressor is carried out using an inverse design method. At the first step of the aerodynamic design, the shape modification capability of compressor meridional plane is generated by linking up the Ball-Spine inverse design algorithm as a shape modification algorithm and quasi 3D analysis code as a flow solver. Then, the meridional plane is modified by improving the hub and shroud pressure distribution and applying it to the inverse design code. At the second part of this research, by developing a novel design method on the blade to blade plane, and incorporating it into the quasi 3D flow solver, the 3D profiles of impellers will be obtained in order to reach the higher blade loading. Finally, to check the outcome of design process, the current and the modified impellers are analyzed using the full 3D flow solver, CFX. The results are the representatives of about 5 percent enhancement in compressor total pressure ratio.

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Increasing the pressure in gas turbine cycle is done by Compressor which is one of the most important components of the Gas Turbines. Due to positive pressure gradient, the nature of the flow inside the compressor is complicated and for this reason and because of the duty of the blade for transferring energy to the flow, precise design of the compressor’s blades from the aerodynamic view of point is very important In this study, effects of changes the rotor blade stagger angle on a transonic axial compressor performance curves including efficiency and pressure ratio has been studied. To simulate the complicated three-dimensional flow field in axial compressors, a numerical code is used to solve Reynolds Average Navier-Stokes (RANS) equations. comparison between numerical results and experimental data shows a good agreement. When numerical code are verified. Then the rotor blade twist changes on axial compressor performance have been studied. The results show that the rotor blades twist leads to decrease in compressor efficiency and pressure ratio.

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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%.

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In the present paper, flow field in all components of a two-stage centrifugal compressor are simulated using one-dimensional method. Internal flow simulating is performed by solving basic equations of corrected empirical relations of geometry, thermodynamics and dynamics with an algorithm with iterative solution was in MATLAB. The purpose of simulation is to obtain the effect of inlet guide vanes and return channel intake angle changes on performance maps. The inputs include stagnation temperature, stagnation pressure and mass flow. The solution is done by calling the primary geometry and inlet thermodynamic and ambient conditions at the nominal speed and 70, 90 and 105 percent of the nominal speed, by applying a continuous flow with convergence of mass flow rate and Rothalpy conservation. Then in performance stability range the results of one-dimensional model are validated by empirical and three-dimensional modeling results. Then the effect of incidence angles of inlet guide vanes and return channel on compressor performance at performance maps are expressed and analyzed. This model can be used to design inlet guide vane and return channel and estimate optimized angle of guide vanes to gain maximum performance and pressure ratio.

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In this research an inverse design algorithm, called ball-spine algorithm (BSA) is developed on a 90-degree bend duct between the radial and axial diffuser of a centrifugal compressor with viscous swirling inflow to bend duct. The shape modification process integrates inverse design algorithm and a quasi-3D analysis code. For this purpose, Ansys CFX software, is used as flow solver and inverse design algorithm is written as a code inside it. Shape modification is accomplished for viscous and inviscid flow to check the effect of viscosity on convergence rate. Also, the effect of swirl velocity in shape modification process is investigated, by considering increased pressure as the target parameter. The algorithm reliability for swirling flow is verified by choosing different initial geometries. Finally, aerodynamic design of the bend duct with BSA is accomplished to reduce losses in 90-degree bend. Shape modification process is carried out by improving the current wall pressure distribution and applying it to the inverse design algorithm. Results show that convergence rate and stability of BSA are favorable for designing ducts with swirling viscous flow. So that, the pressure recovery coefficient of the 90-degree bend duct is 4%increased.

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Direct-expansion solar-assisted heat pumps (DX-SAHP) have been used widely to heat the consuming water of buildings and industrial facilities, domestic and industrial space heating and also, air conditioning. These systems transfer energy from lower temperature source to a higher temperature source. In DX-SAHP systems, In order to optimize the heat transfer of solar radiation to the refrigerant, the flat plate solar collector is used as the evaporator. In this paper, the thermal performance of a DX-SAHP has been studied using numerical simulation for heating the water of a house in Kermanshah. The system mainly employs a bare flat-plate solar collector with a surface area of 4 m2, a hot water tank with the volume of 150 L, a rotary-type hermetic compressor, a thermostatic expansion valve and R-134a is also used as working fluid in the system. The results show that the hours of system operation, during different months in the climate of Kermanshah, vary between 37 to 130 hours and the monthly average COP and the solar collector efficiency vary between 3.96 to 6.71 and 68 to 99 percent respectively. The effect of various parameters, including solar radiation, ambient temperature, collector area, compressor speed, number of collector cover and wind speed have been analyzed on the thermal performance of the system.

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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.

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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.

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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.

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Investigation of spike stall formation and its propagation in a low-speed axial-flow compressor is the main aim of this study. Experimental measurements are performed in a low speed axial compressor test rig. Measurement parameters include instantaneous velocity and static pressure at the stall inception process. For this purpose several hot wire probes and a high response pressure transducer is used in data acquisition procedure. Instantaneous fluctuations of velocity at upstream of the blade row show that spike stall inception is accompanied by flow separation from the leading edge of the rotor blade and formation of a vortex subsequently. This vortical structure extends over the blade span. Stall cell propagates with a circumferential speed lower than rotor wheel speed which is equal to 66% of rotational speed in this compressor. Furthermore, wavelet frequency analysis is employed for detail investigation of spike disturbances and capability of this method in distinguishing the spike stall is presented. Wavelet analysis, by representing the temporal variation of frequency spectrum, shows dominant phenomena in the transient process from stable operation to the stall inception condition.

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In this article the effect of using ejector on the thermodynamic performance of the hybrid heat pump is evaluated. With simulation of the new hybrid-ejector heat pump in the EES software, first the effect of the ejector mixing section diameter on the results is analyzed and it is concluded that a diameter of about 15mm makes the primary energy ratio (PER, the ratio of useful thermal energy output to the total initial heat energy input) and second law efficiency of the heat pump to be maximum and the exit temperature of the compressor to be minimum. Next, PER, second law efficiency and the compressor exit temperature of new heat pump are compared with those of the conventional hybrid heat pump at the same amount and temperature of the input heat. The results showed that the PER and second law efficiency of the new layout is maximum 10 percent and about 18 percent higher than those of the hybrid cycle respectively. It is also observed that with considering the restriction in compressor exit temperature, in new system, it is possible to increase the temperature of input heat 35C more compared to the increase that can be occurred in the hybrid system. Finally, the analysis of the relative exergy losses in the components of the systems revealed that in the new layout, the relative exergy losses of throttling valve, desorber, compressor and absorber were reduced and improved the performance of this cycle.

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Compressor and their blades are one of the most important parts of gas turbines. Based on recent reports, failure of compressor’s blades was one of the major cause in malfunctioned t56 gas turbines. In this study, propagation rate of a crack within the compressor blade of a T56 jet engine has been investigated. To this end, centrifugal and aerodynamic forces acted upon the blade has been calculated and their corresponding stress field has been simulated in ANSYS software. Spots at the maximum risk of foreign object damage and corrosion had been located, and their bending and tension stresses had been calculated via employed simulation. Subsequently, an initial half elliptical crack has been created on all of previously located spots, and their stress intensity factor using Raju-Newman method has been determined. Finally, by using Paris law fatigue life and crack growth rate of each cracks has been extracted, individually. Results indicate a drastic decrease in fatigue life of blades when crack located close to the blade’s root. Furthermore, cracks located on the suction surface has remarkably shorter fatigue life than those which are located on pressure surface, in comparison.

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In axial flow compressor there is a gap between stationary and rotating members since the stator vane is fixed at the casing and the shaft is rotating at the root. Also, the pressure increases when the air flows through the stator vanes. Therefore, due to pressure increase and existence gap under vanes, the leakage is inevitable in the stator tip. This leakage can change the flow pattern near the stator tip, which causes more separation. Therefore the loss has been increased so it adversely effects on performance. In this paper, the effect of stator tip sealing with honeycomb on compressor performance is investigated. For this purpose, the 9th stage of a ten-stage compressor is examined in two cases of solid wall and sealing with honeycomb. The numerical results have good agreements with experimental results. The results show that by reduction of leakage at stator tip, the size and depth of tip corner separation decreased significantly leading to loss reduction. Also the effect of the leakage on flow angles shows that to have more accurate analysis of compressor performance, it is necessary to be considered the stator tip leakage. On the other hand, according to same effect of honeycomb on reducing stator tip leakage than solid wall, here the honeycomb roles as an abradable material to prevent direct contact between rotor and stator. Also in analysis of stage the honeycomb can be replaced with solid wall model.

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The numerical simulation of near-stall condition in a passage of an isolated subsonic rotor is studied in detail. The requirements of numerical simulation in order to resolve turbulent spectra around the blade are studied. According to the fact that most of unsteady aerodynamic phenomena incept from blades leading edge, and the role of this part in types and intensity of instabilities, the goal of this paper is to investigate the effects of changes in radius of leading edge of airfoil on flow phenomena in different scales of wave numbers. The governing equations of flow-field are solved using different numerical approaches. Resolution characteristics of different modeling and simulation techniques are investigated. The primary geometry of blade uses a standard NACA-65 series airfoil, which has been tolerated by 50% variation in circular leading edge radius. Mesh requirements of flow simulation for intended purposes are studied in detail and some recommendations are proposed to be implemented in numerical aeroelastic simulations. Accuracy and fidelity of LES results are studied with extraction of power spectra around the blade and the portion of resolved energy is also estimated. Results suggest that the order of accuracy and grid density highly affect the small-scale flow phenomena. The variations in leading edge radius also have great effect on energy distribution among resolved scales.

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To transport the natural gas from the producer sources to the consumers, gas pipelines are used. The extension of the pipelines reduces gas pressure and compression stations are considered to compensate for the loss of pressure in the transport path. At these stations, several compressor units usually work in parallel to share the gas inlet flow. The purpose of the present study is to investigate the load distribution method between parallel compressors in an optimal manner according to the capacity of each compressor. In this paper, a load sharing algorithm is proposed with the help of a model-based predictive controller (MPC) to achieve a stable and efficient operation at the compression station. In this algorithm, real-time optimization is used by an adaptive modifier method when faced with a variable demand from the consumer. The optimization is done according to the capacity of each compressor and using the approximated efficiency curve. In this way, the coordinates of the optimal working points for each compressor are obtained. The proposed algorithm is implemented in MATLAB software on the dynamics of centrifugal compressors in parallel arrangement. The results show that the load distribution using the proposed method has a much better performance than the old methods such as equal load balancing. This method results in the optimal operation of each compressor and thus storing and saving the natural gas.

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1.4923 stainless steel is one of the options for producing Iranian gas turbine (IGT25) compressor blades and upgrading IGT25 +., as well as the importance of wear resistance in turbine parts and the small number of studies in the field of wear as a destructive mechanism of turbine parts, in this research the effect of residual stress caused by shot peening on the wear resistance of steel 1.4923 was investigated. To create the compressive residual stress, shot peening operations were used at 5, 10, 15 and 20 minutes. Microstructural studies by optical microscopy (OM) and scanning electron microscopy (SEM) showed that with increasing shot peening time, the thickness of the plastic deformation area increases so that the plastic deformation area can be divided into three plastic deformation areas. Severe, ordinary plastic deformation and the area affected by plastic deformation. Calculations on the results of X-ray diffraction (XRD) showed that with increasing shot peening time, the amount of compressive residual stress increases to 694 MPa. With increasing compressive residual stress on the surface, the wear resistance of the samples increased up to 90% due to the increase in the density of dislocations and grain refining.  Also, the investigation of worn surfaces by SEM showed that the wear mechanism in the samples is oxide adhesive wear and increasing the residual stress of the samples causes the transfer of the wear regime to mild wear abrasion with the appearance of crater areas.