The first step in the investigation is to characterize the flow when the second blade of the tandem blades is positioned in the "no gap nozzle effect", Figure 13. The interaction between the two blades is only evident in terms of the wake of the front blade that affects the flow behavior along the arrangement. To characterize the influence of the second blade position, different values are given for the axial and tangential displacements of the second blade. Figure 14 shows a graphical representation of the front blade's trailing edge with the possible second blade locations in terms of the axial and tangential displacements. There are a range of three axial displacements that varies between 0 and 0.2 and a range of five tangential displacements that varies between 0.15 and -0.15. These two ranges represent relative position of the rear
First of all, the complex secondary flows and significant boundary layer separation, as well as the interaction of the low-momentum fluid in the boundary layer with the tip leakage flows result in the impeller outlet flow non-uniformity in which the low-velocity wake region is close to the suction surface and jet region near the pressure surface of the blade. This flow pattern is called the “jet-wake” flow >5@, >6@. The mixing of this “jet-wake” flow is the source of significant loss generation. The outlet flow velocity field is non-uniform both in circumferential (pitchwise) and in axial (spanwise) direction. While the circumferential variations in the outlet flow level up very rapidly, at the same time the axial variations in the flow seem to persist well into the diffuser. This axialflow variation has an adverse effect on the pressure recovery of the diffuser (vaned or vaneless) and it is one of the main causes of stage instability in compressors. Therefore, the minimization or possible suppression of the formation of the outlet flow non-uniformity should not only lead to substantial improvement in stage performance but also result in increases in the stable operating range of the turbomachine.
Secondary Flow Experimental Study for Axial Compressor Cascade Strong Stagger With and Without Tip- Clearance: Static Pressure Distribution on Blade Surface. The performance of blade cascade is influenced by the growth and boundary layer’s separation along blade surface and endwall (casing and hub). The secondary flow which happens near hub and casing compressors is three dimentional flow separation phenomenon comes from interaction blade boundary layer with casing and hub boundary layers in the compressor. The secondary flow causes secondary losses, blockage effect, and turning angle (deflection) distribution along blade span. The result of the research shows that the increase of the angle of attack reveals lines of constan pressure to be curved forward (upstream) or pressure gives rise to spanwise caused by a strong curl flow. Separation is also increase and cross between two blades. Hence, three dimentional separation region in corner also increase.
Numerical study is performed to investigate the swirling flow around a rotating disk in a cylin- drical casing. The disk is supported by a thin driving shaft and it is settled at the center of the cas- ing. The flow develops in the radial clearance between the disk tip and the side wall of the casing as well as in the axialclearance between the disk surfaces and the stationary circular end walls of the casing. Keeping the geometry of the casing and the size of the radial clearance constant, we compared the flows developing in the fields with small, medium and large axial clearances at the Reynolds number from 6000 to 30,000. When the rotation rate of the disk is small, steady Taylor vortices appear in the radial clearance. As the flow is accelerated, several tens of small vortices emerge around the disk tip. The axial position of these small vortices is near the end wall or the axial midplane of the casing. When the small vortices appear on one side of the end walls, the flow is not permanent but transitory, and a polygonal flow with larger several vortices appears. With further increase of the rotation rate, spiral structures emerge. The Reynolds number for the onset of the spiral structures is much smaller than that for the onset of the spiral rolls in rotor-stator disk flows with no radial clearance. The spiral structures in the present study are formed by the disturbances that are driven by a centrifugal instability in the radial clearance and they are pene- trated radially inward along the circular end walls of the casing.
Characteristics of rotor blade tipclearanceflow in axialcompressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper contributes to the investigation of 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 bound walls, tip leakage flows, secondary flows, swirl effects, streamlines curvatures and pressure gradients along different directions. Therefore, 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 tipclearance 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, timescale, and lack of effective damping coefficient. This leads to dissipation of vortical structure of flow and wrong estimation of the flow field at the rotor tipclearance region. Nevertheless, k-ω- SST turbulence model provides results consistent with reality.
4.2 Study of Numerical Approach: - Numerical approaches were studied on the basis of two methods. First one was the CFD (computational fluid dynamics) and other one was FEM (Finite element method). CFD, its branch of fluid mechanics that uses numerical analysis and data structures to solve and analyze problems that involve fluid flows. The effect of change in speed of fan on velocity pressure and mass flow rate of the axialflow fans was investigated by using CFD software. It was seen that the significant change in mass flow rate, velocity of rotor and stator vanes as the speed of the fan is varied . The influences of the inlet air flow distribution on the performance of heat exchangers. The ranges and values of the geometry of the heat exchanger are studied by the CFD simulation.
In industrial applications, CFD is an important tool to aid in the design and validation of turbomachinery components. However as with any CFD simulation, there are many sources of error that can lead to incorrect or unrealistic solutions. Some sources of error specific to turbomachinery relate to modelling approximations such as the use of idealized geometry in tipclearance regions, incorrect transition modelling, the use of mixing planes, and perhaps the largest approximation: the assumption of steady state flow (Denton, 2010). Due to the limitations of current CFD techniques, many of these assumptions are unavoidable; however one source of error that can be reduced is in turbulence modeling. Efforts are constantly being made to examine and improve readily available eddy viscosity turbulence models. Many researchers have investigated the use of different RANS based eddy viscosity models to predict turbomachinery performance. Some models are more suitable than other for these types of simulations. When simulating turbomachinery, models need to be able to cope with high Reynolds number flows as well as complex flow dynamics such as separated flows, tipclearance vortices, rotating to stationary reference frames, and flow effects by curved surfaces. Some researchers have investigated uncorrected turbulence model performance in turbomachinery applications and others have investigated curvature corrected models such as the curvature/rotation corrected Spalart-Allmaras model (SARC) (Spalart & Shur, 1997).
has been utilized, enhanced, and validated in support of these endeavors. In the research which follows, TURBO is shown to accurately capture compression system flow range—from choke to stall inception—and also to accurately calculate fundamental aerothermodynamic performance parameters. Rigorous full-annulus calculations are performed to validate TURBO’s ability to simulate the unstable, unsteady, chaotic stall inception process; as part of these efforts, full-annulus calculations are also performed at a condition approaching choke to further document TURBO’s capabilities to compute aerothermodynamic performance data and support a NASA code assessment effort. 8. EFFECTS OF TIPCLEARANCE ON ROTOR/STATOR INTERACTION TONAL NOISE OF AXIAL FAN By Liangfeng Wang, WeiyangQiao, Weijie Chen, Liang Ji The tip leakage flow is crucial importance for the turbomachinery design and operation for its contribution in loss and noise production. This study is focused on the effects of tipclearance(TC) on tonal noise behavior of a single stage axial fan. The flow-field/acoustic- field hybrid model is used to evaluate the tonal noise level from a time-accurate CFD result. The hybrid model is based on the three- dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations and the ducted blade-rows aerodynamics and aeroacoustics(DBAA) theory. The results indicate that the high amplitude areas of unsteady loading fluctuation are mainly around the leading edge of stator vane, and the effect of TC on the noise source distribution is mostly in the tip region. The varies of total acoustic power level is less than 1dB as the TC is changed from 0mm to 1mm. The effect of TC on the total acoustic power level is not same for different frequency or different propagated direction.
The objective of this paper is the numerical study of the flow through an axial fan and examining the effects of blade design parameters on the performance of the fan. The axial fan is extensively used for cooling of the electronic devices and servers. Simulation of the three-dimensional incompressible turbulent flow was conducted by numerical solution of the (RANS) equations for a model. The SST- k- ω and k-ε turbulence models are applied in the simulations which are done using CFX software. The comparison between available experimental data and simulation results indicates that the SST k-ω model gives more accurate results than the k-ε model. The results also show that in separation regions and vortices, the pressure will decrease. Hub area and blade root contain large vortices . The effects of changes in the blade geometry and the number of blades on the fan performance are studied in detail. For the primary fan model with the different number of blades (4, 5, and 6), the maximum mass flow rate of 800 CFM is obtained. Hence, the number of blades had negligible effects on the maximum flow rate. By 3o% decreasing in the chord of the blades, the maximum mass flow rate of the fan with the different number of blades (5, 6 and 8) will be reduced to 500 CFM. Therefore, in order to increase the maximum mass flow rate, the chord and the width of blades should be increased. On the other hand, by increasing blades from 4 to 6 in the primary model, the maximum outlet pressure has been increased by 32%. Furthermore, it was found that in high flow rates, an increment in the number of blades had no effect on the produced static pressure.
It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is slower at a lower altitude, so less wind energy is available for a given sizeturbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten its service life (Edwards, J.M., et al., 2012; RacitiCastelli, M., et al., 2011; Bhutta, M.M.A., et al., 2012). However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at theturbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum formaximum wind energy and minimum wind turbulence.
101 The proposed concept of the journal bearing with semi- active control provides necessary preload and also an additional number of converging & diverging zones for attenuation of vibration especially at critical speeds. The preloading of flexible sleeve using supports with knob (S1, S2, S3 and S4) increases the pressure and also the number of pressure zones. In the conventional circular bearing during rotation (for certain viscosity of the fluid, speed and load), the journal reaches a certain eccentric position due to hydrodynamic lift. Due to fluid flow in the converging zone or wedge (the result of eccentricity), the pressure will develop at the bottom portion of the journal bearing, and this pressure leads to hydrodynamic lift of shaft thus load carrying capacity.
the first pod is close to the soil and the combine harvester does not cut closer to the soil, weeds are clogged in the threshing system, and percentages of loss and breakage after harvest are over 7.9 and 17.4%, respectively . Moreover, the diversity of soybean plots makes it inappropriate to use large machines. All of these problems are required to be solved. Nowadays, more farmers turn to use small tractors, and many of them own a tractor as the initial power of transporting and trailing various farm labor-saving devices. Therefore, there are more needs to develop trailer devices or certain installments for more use and benefits from farm machinery. Nakqoue  said that a small soybean combine harvester suitable to the plantation is not very expensive, and small and potential farmers are able to purchase one from the producer in order to contract soybean harvest in their locality. This is one way to reduce soybean production cost. The machine is efficient in terms of its performance and hence product loss is lowered. In fact, soybean production has faced a problem in harvesting and threshing because it needs human labor. This problem can now be solved by installing a farm tractor with a soybean combine harvester, which has been designed and manufactured for a 22 HP farm tractor of a 1400 width x 5,000 length x 2,200 height mm size. This device comprises a reaper head, a conveyor, a thresher, a cleaning unit, and a 4 Ft (1.2 m) axialflow rotor. A. Chirattiyangkur et al.  design and development of a tractor mounted soybean combine harvester showed that the machine has a capacity of 0.0944 ha/h, with an efficiency of 42.37%. The percentage of loss is lowest when operating at the reel index and cutter speeds of 1.0 and 0.5 m/s, respectively
2.1 Description of applied models A cracked tube was modeled by means of the finite element method (computer code PAFEC-FE I8I, I9I). Two models of the axial crack were developed. The first one was composed of 3-D fi nite elements (Fig. 1), the second of shells (Fig. 2). Both models represent a crack with zero width and length of 2a = 12 mm. Zero width is very convenient from the modelling viewpoint and, at same time, models the highest stress concentrations at the very sharp crack tip.
In this study, inlet-nozzle angles are varied at (5̊, 10̊, 15̊, 20̊, 25̊, 30̊) and diffuser angles are (5̊, 10̊, 15̊) respectively. Diameter of throat, diffuser length and inlet-nozzle length are fixed. Diffuser model is prepared using AutoCAD as shown in Fig.4. Numerical simulations for different angles of inlet-nozzle diffuser were performed to analyze flow characteristics by deploying an unstructured grid finite volume methodology using commercial CFD software (ANSYS CFX 17.0). The accuracy of results produced through a CFD calculation is reliant upon the mesh that is provided for analysis. Basic meshing techniques consist of a structured or unstructured mesh comprised of one of several element types. In this research, the mesh statistics are 106,608 nodes, 553,620 elements.Fig.4 (a) shows the geometry of inlet- nozzle diffuser and Fig.4 (b) shows the mesh of inlet- nozzle diffuser.
Patel, Zeckhauser, and Hendricks (1992) and Kane, Snatini, and Aber (1991) reported that previous fund performance adjusted for risk appears to be associated with net inflows into mutual funds. However, Sirri and Tufano (1992) found that raw returns, which are not adjusted for risk appear to drive fund growth. They suggested that "naive retail trend chasers" are even more responsive to the "noisier" measure of unadjusted performance. Recent research by Huang, Wei, and Yan (2012) and Barber et al. (2016) established that investors take into account Jensen’s alpha estimates when allocating capital to mutual funds and that most are sensitive to a fund’s alpha. Moreover, literature suggests that the relationship between fund flows and returns tends to be convex (non-linear); positive returns garner more inflows than the outflows lost due to negative returns (Chevalier and Ellison, 1997; Sirri and Tufano, 1998, Ferreira et al., 2012). Ferreira et al. (2012) analyzed the relationship between flows and performance in a group of 28 countries (excluding Israel) and found a convex relationship worldwide between these two factors, with higher convexity in less developed countries.
The microchannel heat exchanger promising with its superior thermal performance. For conventional channel the thickness of separating wall comparatively small to the hydraulic diameter of the channel, therefor the effect of axial heat conduction may be neglected in conventional heat exchanger. But for microchannel heat exchanger thickness of separating wall comparatively large to the hydraulic diameter of the channel. The microchannel heat exchanger gives extremely high heat transfer area per unit volume over a conventional channel . Mehendale et.al  classified the channel ranges from 1 to 100 µm as microchannels, 100 µm to 1 mm as meso-channels, 1 mm to 6 mm as compact passage, and greater than 6 mm as conventional channel.
This observation is also supported by examination of a typical set of simultane- ously acquired quasi wall shear stress traces shown in the lower part of Fig. 7.13. Patches of turbulence are observed to convect in the free-stream direction. A large suction surface flow separation would be expected to cause reverse flow near the trail- ing edge with disturbances convecting in the opposite direction to the free-stream flow. The two sensors closest to the trailing edge show very low levels of quasi wall shear stress between patches of turbulence; the disturbance amplitudes are falling rapidly with a tendency for the disturbance convection velocity to decrease. In addition, the corresponding surface pressure measurements shown in Fig. 7.5 show a small pressure recovery toward the trailing edge: this is significantly greater than the pressure re- covery in the low Reynolds number case (Re c = 75000). These observations suggest