sarallah abbasi

One of the factors that can cause a reduction in the efficiency and performance of axial compressors is the tip leakage flow of the compressor blade. In the first, the compressor's performance curve is compared with experimental results obtained under the condition of no air injection, and a statistically significant agreement is observed. The present study investigates the impact of various parameters, including flow rate, diameter, angle, and injection location, on the compressor's performance curve and flow structure, taking into account the injection of air into a passage. The results indicate that the compressor's stall margin and stable range extension are at their maximum values at a specific scale of each of the aforementioned parameters. Any deviation from this scale, either by reducing or increasing the injection parameters, leads to a reduction in the above characteristics. Although the presence of injection leads to an increase in the total pressure ratio in all injection states compared to the state without injection, the adiabatic efficiency at similar mass flow rates exhibits no significant change. The results also indicate that flow injection in the most suitable state increases the stall margin amount by 27% and the stable range extension of the compressor by 192.

In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, the effect of these parameters on the thrust, thrust specific fuel consumption (TSFC) and engine efficiency was investigated and then in the exergy analysis, it was found that the lowest exergy efficiency with a value of 85.45% belongs to the combustion chamber; Therefore, a parametric study was conducted to improve the performance and exergy efficiency of the burner; For example, in the case of bypass ratio of 2.2 and fan pressure ratio of 2, the exergy efficiency of the burner is increased by 12.23% compared to the base case. In addition, the results of sensitivity analysis show that the burner exit temperature and the HPC pressure ratio with 21.81 and 2.2%, respectively, have the most and the least effect on the engine net thrust; Also, the burner exit temperature and the flight altitude with 4.57% and 0.11%, respectively, have the most and the least effect on the TSFC.

Tip Leakage flow of the compressor blade is one of the effective factors in performance of axial compressors, which can also damage the compressor blades. In this paper, the effect of air jet injection to reduce the destructive effects of tip leakage flow on the performance of the axial compressor is investigated. For this purpose, the numerical analysis of the flow in the NASA rotor 37 axial compressor is performed using CFX software. Initially, the compressor performance curve in the without injection mode was compared with the experimental results and a good agreement was observed. Then, considering the injection of air for one passage the performance curves of the compressor in comparison with the non-injection mode were examined. By injecting air, the pressure ratio increases and the adiabatic efficiency of the compressor decreases at the same mass flow rates. It was found that air injection reduces the drops in the axial compressor and weakens the created vortices. This reduces the rotor drop coefficient and also reduces the angle of attack. Accordingly, injection increases the stall margin and increases the operating range of the compressor by 6% and 66%, respectively. Also, the tip leakage flow has less power than in the without injection condition, which results in less drop.

The purpose of this paper is to investigate the effect of aspect ratio on vortex shedding, and transient flow-induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model  are employed to flow analysis. Aerodynamic noise calculations are performed using the FW-H analogy. The rectangular cross-section with various lengths and widths is considered. A comparison of the results extracted in the present study with the experimental results of other references indicates the accuracy of the present research. The aspect ratios from 0.6 to 6 (equivalent to Reynolds numbers from 2.5 × 104 to 5.6 × 104) are studied. The simulations can be divided into two categories. In the first category, the ratio of length to width (R = B/H) is less than one, and in the second one, this ratio is greater than one. In the first case, noise is reduced by a relatively low slope. But in the second condition, the behavior of noise is different in various ratios and the slope of noise variations is high. The flow structure is also discussed in this paper. It is founded that for the first category, by increasing the aspect ratio, both the fluctuations and aerodynamic forces are reduced, and the longitudinal wake zone is increased. But in the second category, fluctuations of flow may be increased or decreased in various aspect ratios.

In the present paper, the numerical simulation of the flow to identify the cavitation and its effects inside the centrifugal pump of 100-250 type of Pumpiran Company, including the impeller and volute of the pump, has been done. The Rayleigh–Plesset equation was employed to study the growth and collapse of the vapor bubble. In order to validate the numerical results, the pump curves were extracted from the present study and compared with similar experimental. The deviation of the present numerical results with the experimental ones in the pump design flow rate is 6.5%. It is found that cavitation occurs at inlet pressures of less than 45 kPa. By reducing the inlet pressure from 40 kPa to 20 kPa, the flow separation rate also increases and its position is transferred from the beginning of the blade to the inner areas of the blade. The position of cavitation occurs at 0.14 to 0.24 of the passage as well as at the beginning of the blades. The volume fraction of steam in these parts has increased from 0.04 to 0.96, respectively. With cavitation in the net positive suction head equal to 1.52, a 3% drop of the head is observed in the diagrams.

In this paper, the effect of blowing in a rod on the flow structure and its noise in a rod-airfoil is investigated. To this aim, the simulation of the flow around the rod-airfoil was performed using URANS equations and employing k-ω-SST turbulence model. . The prediction of the flow-induced noise is performed using F-WH analogy. Since Vortex's periodic producing is the main cause of the noise mechanism, by reducing its effect on the airfoil leading edge, the acoustic propagation reduces as well. In the present study, in order to control flow and reduce noise, the blowing active control in the rod has been used. The intensity of the blowing (I) is chosen between 0.1 and 0.5 where I is the ratio of blowing velocity to the inlet freestream flow). The results showed that increasing the blowing intensity to 0.5 reduces the noise emitted from the rod by 90% and the airfoil and rod-airfoil by 64%. In addition, by applying blowing, the lift force is increased and the drag force of the rod is reduced, which is aerodynamic favorable. In addition, the vortex shedding frequency is decreases while blowing applied.

In This paper, a parametric study of compressor performances was performed by streamline curvature method (SLC). Effects of three input parameters in design process, e.g., number of blades, distribution of blade thickness, and blade sweep angels, on the main objective parameters in aerodynamic design, e.g., velocity distribution, efficiency and pressure ratio, has been investigated in the parametric study. Initially, a certain two stage axial compressor has been designed by SLC. Validation of the results is confirmed by comparing the obtained results with the experimental ones. Regarding various values for aforementioned input parameters, the first stage of the axial compressor is redesigned and the output parameter is established. Therefore, the sensitivity of the design results to each of the aforementioned parameters is recognized. Results show that increasing the blades sweep angle causes to improve the flow behavior such as efficiency and pressure ratio in axial fan and reducing it have a completely contrary result. Also, reducing the rotors blades number leads to an increase in the pressure ratio and efficiency while its increase cause to a contrary result. , it is concluded that reduction in the blades number has the stronger effect on the performance parameters than its increment. The results also show that effect of the thickness in the hub is greater than the thickness of the tip and its increase leads to reduce both efficiency and pressure ratio.

The choice of geometrical shape of the blades has a considerable effect on aerodynamic performance and flow characteristics in axial compressors. In this paper, the effects of the blades shape on the aerodynamic design characteristics are investigated based on Streamline Curvature Method (SCM). Initially, the Streamline Curvature Method (SCM) is used for designing a two-stage axial compressor. Comparing the current results with experimental ones indicates good agreement. The first stage of the axial compressor is selected with three different blade profiles. The first case (case I) has the polynomial camber with naca thickness distribution series 6. The second case (case II) has the standard naca profile series 6 and the third case (case III) has the modified standard naca profile series 4. Results reveal that using the standard airfoils in the stators leads to improved flow conditions such as loss coefficient and pressure ratio. On the contrary, this profile selection may cause an increase in the stagger angle that is not favorable. Aerodynamic Design with a polynomial camber line in the rotor demonstrates a better aerodynamic behavior in loss coefficient, pressure ratio and diffusion factor. Whilst the use of such a camber line in the stator leads to the formation of less favorable aerodynamics conditions in comparison to the standard airfoil.

In this paper, a numerical study of the overall performance and flow structure in an axial turbine and the effect of a film cooling on it are discussed. For this purpose, two-stage axial turbine is simulated and numerically analyzed using the ANSYS-CFX commercial software. Various analyzes have shown that the rate of blowing ratio (B.R) equaled 0.82 and the velocity ratio (V.R) equal to 0.4 with a 30 degree jet angle is suitable for cooling holes. Of course, because of the high importance of leading edge and coolant inject to the stagnation region, as well as increasing the temperature at the pressure side relative to the suction side, there is a higher flow rate for cooling in these areas. The study of the turbine performance curve shows a slight reduction in the pressure ratio and efficiency due to the application of cooling, which can be compensated by the possibility of increasing the inlet temperature. The streamlines around the blade provide a layer of flow with low temperatures, which is an obstacle between the hot flow and the blade surface. The application of cooling reduces the temperature of the pressure and suction surfaces of the blade at about 300 ° C and the temperature of the front surface of the blade is about 200 °. Investigating the radial and axial variations of the thermodynamic parameters indicates that, by applying the cooling, the mach number and total temperature of the flow at inlet and outlet are reduced and the pressure drop increases.

Characteristics of rotor blade tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper is contributed to investigate tip leakage flow in a low speed isolated axial compressor rotor blades row. Simulations are carried out on near-stall condition, which is valuable of being studied in detail. In turbomachines, flows are non-isotropic and highly three-dimensional. The reason arises from the complicated structure of bounded walls, tip leakage flows, secondary flows, swirl effects, streamlines curvatures and pressure gradients along different directions. As a result, accurate studies on tip leakage flow would be accompanied by many challenges such as adopting suitable turbulence models. So, investigations are carried out numerically utilizing two well-known turbulence models of k-ε and k-ω-SST, separately. It is shown that the k-ε model yields poor results in comparison to the k-ω-SST model. To realize reasons for this discrepancy, turbulence parameters such as turbulent kinetic energy, dissipation and eddy viscosity terms at the tip clearance region were surveyed in detail. It is found out that estimation for eddy viscosity term is too high in the k-ε model due to excessive growth of turbulent kinetic energy, time scale, and lack of effective damping coefficient. This leads to dissipation of vortical structure of flow and wrong estimation of flow field at the rotor tip clearance region. Nevertheless, k-ω-SST turbulence model provides results consistent with reality.

Turbine tip leakage flow is one of the effective factors in reducing the efficiency and performance of axial turbines, which can also destroy turbine blades. Accordingly, it is important to identify and control the tip leakage flow. In this paper, we investigate the effect of tip clearance sizes and changes in tip shape as a passive control method on tip structure and total turbine flow performance. For this purpose, the flow loss in a two-stage axial turbine is performed using the CFX software. In order to ensure the accuracy of the results, the turbine performance curves were compared with the experimental results which good consistency have been observed. Considering the four cases for tip clearance size, the turbine performance curves and resulting pressure loss have been investigated. It was found that increasing the tip clearance size leads to reduced efficiency and increased losses in the axial turbine. In the following, we examine the application of the passive control method through the change of the tip geometry. In this regard, the shape of the blade tip is somehow considered that the tip clearance size is variable from leading edge to trailing edge. The results show that in these cases, tip leakage flow and the resulting vertices are weakened, which leads to a decrease in the rotor loss coefficient. Observing the flow contours results in lower temperatures in the blade region due to the formation of a weaker tipping leak flow, which helps cool the turbine blades.