The common target for vehicles has always been lowest fuel consumption. This paper deals with a new cooling fan for vehicle engine. This fan is used as a cooling fan at low speed or when the vehicle needs cooling. This fan is also used as a wind turbine and generates electric power at high vehicle speed. The fan has possibility to reduce the vehicle air resistance along with the regeneration of the electric power. We have developed a fan rotor that can operate as cooling fan with the same performance as the current fan and can operate also as a wind turbine at higher performance than the current fan. In this paper we report the influence of blade solidity on the wind turbine efficiency. The effectiveness of this proposal has been confirmed through the wind tunnel tests and CFD calculations.

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For design of large wind turbines, effects of structural oscillation of turbine system have to be taken account into load analysis, since oscillation amplitude of blades and tower can be increased considerably for those turbines. The present study deals with a calculation model which can evaluate the aero-elastic effects on the rotor characteristics of horizontal axis wind turbine (HAWT). Using weakly coupled fluid-structure analysis model, effects of structural oscillation of turbine blades as well as the existence of the tower have been examined for the characteristics of the structural loads. The effects of inflow turbulence are also examined on the fatigue load on the turbine structure. The validity of the proposed model is examined by comparing the calculated results with measurement.

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We discuss a factor characterizing diverging/converging rotational speed of small wind turbines by using a model differential equation. In this study, we focus on form of torque coefficient profile and discuss influence of this form on temporal variation of rotational speed.

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In recent years, many wind farms, which mean a group of wind turbines constructed in the same site, are installed globally. In wind farms, energy deficit occurs when the downstream wind turbine operates in wakes generated by upstream wind turbines. Especially in large wind farms, the wakes overlap each other and it forms complex flow field due to the wake interference. In this study, wind speed distributions in wake generated by two test wind turbines were measured by wind tunnel experiment. A calculation model for overlapped wake is proposed and compared with the experimental results in order to clarify the wake interference effect.

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There are two types of VAWT, drag type and lift type. Drag type starts up in the low wind velocity condition, but peripheral velocity does not exceed the wind velocity. As for the lift type, peripheral velocity can exceed the wind velocity, but it does not start up in the low wind velocity condition. A new blade cross section, Magatama, has been proposed. This Magatama section may have both advantages of drag and lift type. The rotary torque was calculated by 2D unsteady numerical simulation. In this simulation the rotor that has three Magatama blads rotates. The parameters are wind velocity, rotation speed, and blade setting angle. Results obtained by this numerical simulation are as follows. The blade setting angle decreases with the rotary torque increases. There is a limit rotation speed to rotate. If the rotation speed exceeds this limit the rotor generates negative torque which is unrealistic.

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This study aims to improve the start-up performance of the drag-type VAWT by placing a defensive vane just upstream of VAWT rotor. Parametric study changing position of defensive vane and wind velocity reveals there is the most suitable position for the defensive vane. The closer defensive vane to the rotor the higher the rotation speed. The defensive vane should be located perpendicular to the wind direction. Torque measurements of VAWT rotor shows defensive vane increases torque three times higher than that without defensive vane.

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This study investigated the effects of tip-speed ratios λ on the flow characteristics around and performance of a cross-flow wind turbine. Two-dimensional computational fluid dynamics (CFD) simulations were performed for the flow field around the wind turbine. The CFD results confirmed that with an increase in λ, the torque generated by a blade was generally decreased on the upstream drive side due to the decrease in the relative wind speed against the blade. It was also confirmed that negative torque was generally increased on the upstream return side of the wind turbine due to the increase in the relative wind speed against the blade and in the scale and strength of the vortices trapped between the blades.

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Three dimensional computational fluid dynamics (3D-CFD) had been carried out to simulate the flow field around an aluminium circular-blade butterfly wind turbine (ACBBWT), which is a vertical axis type with four circular blades and whose diameter is 2.06 m. Under the assumption of a loss factor of 0.8 due to generator and AC-DC converter and so on, the CFD results agreed with the experimental results. Although vortex shedding corresponding to tip-vortex was observed at the top and bottom portions of blades, the vorticity intensity was weaker than the straight-bladed rotor case and the vorticity-distribution shape seemed to be elliptic unlike a circle. In the cases of low tip speed ratio, vortex shedding was observed at the downwind half-cycle as well as the upwind half-cycle.

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We investigate a streamwise localized solution in plane channel flow obtained by shooting method. This solution becomes more unstable at lower Reynolds number and does not lead to a stable attractor. In addition to this, a chaotic edge state is also on a boundary of turbulence and laminar state. Observation of the structure of the solution indicates that early process in development to turbulence governed by its instability exhibits splitting of low-speed streak.

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An invariant object on the laminar-turbulent boundary in phase space called the "edge state" is investigated for the pressure-driven flow through a square straight duct. For a long duct with the streamwise period of 8πb_* (b_*: half the duct side), the edge trajectory settles down to a flow with streamwise localized disturbances. The localized edge state is converged into the travelling wave by using the Newton-GMRES method.

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Direct numerical simulations were carried out to study large-scale intermittent flow structures in the rotating plane Couette flow. The intermittent flow structures consisting of turbulent and non-turbulent regions were observed in the near wall region, while the flow became homogeneous in the channel center. This intermittent flow structures at each walls were sandwiched by high- and low-speed fluids existing upwind and downwind turbulent regions, respectively, and formed stripe pattern. The stripe was distributed in the region of 0 < y^+ < 100, where y^+ represents the distance from the wall normalized by the wall unit, and the above region was non-intermittent turbulence. The region containing of the stripe pattern was affected by the turbulent diffusion, while turbulent diffusion became negligible and turbulent production balanced with turbulent dissipation in the other region.

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We study edge states in the large-domain plane Couette flow. The simple edge state in the minimal Couette flow is sub-harmonically unstable in the large-domain, and we find a steady simple edge state which has broad-streamwise-six waves. It may be expected that this edge state bifurcates into a localized edge state as the length of domain increases.

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Direct numerical simulations (DNSs) are used to analyze a flat-plate turbulent boundary layer with separation and reattachment. In the present DNSs, the strong blowing and suction are imposed at the upper boundary for producing a large turbulent separation bubble, thus dealing with massive separation. Particular attention is given to unsteady motion of the bubble.

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Laminar-Turbulent transition of a boundary layer forced by a jet in the inlet region of a circular pipe was experimentally investigated. The jet was injected radially from a small hole in the inlet region into the pipe flow periodically. Isolated turbulent patches were formed from the jets, and then they propagated downstream. Axial and radial velocity components were measured by a hot-wire anemometer. Mean and fluctuating velocities and intermittency function were ensemble-averaged. The contour maps of the intermittency were drawn. Isolated turbulent patches grow by an entrainment of non-turbulent fluid from the leading edge and trailing edge. In particular, the entrainment from the leading edge with the velocity gradient is only near the wall. This contributes to increase in fluctuating velocity there. Isolated turbulent patches grow in not only axial direction but also circumferential direction. The circumferential growth causes the radial velocity component.

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FAC (flow accelerated corrosion) is a phenomenon that accelerates the wall thinning rate in the flow. Mass transfer coefficient k is one of the important parameters to evaluate pipe wall thinning rate. We measure mass transfer coefficient by electrochemical technique and flow field using stereo PIV in order to observe the relationship between wall thinning and flow field. Based on the previous studies, we can expect that not only flow in the inner layer but also flow in the outer layer affects the mass transfer from the wall surface. Then, we calculate the correlation coefficient of amplitude modulation to observe interaction of inner and outer layer in this study.

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Experimental analysis for determining the general relationship between surface roughness and flow resistance has been performed. In this study, we measured the actual flow resistance on the rough wall with regularly distributed rectangular ribs by using the concentric cylinder device and velocity distribution was also measured by LDV. Based on the present result, we proposed a simple equation for predicting flow resistance over rough wall. For making the equation, we evaluated the factional drag and pressure drag acting on the surface of ribs separately by the measured velocity distribution. Consequently, we can also estimate total flow resistance. Compared the estimated flow resistance by measured velocity distribution with the actual flow resistance measured by toque of the inner cylinder, these results had good agreement and validity of a simple prediction equation was confirmed.

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The complexity or randomness was examined with the aid of Kolmogorov complexity for the flow about a turbulence wedge developed from a single roughness element on a flat plate. Velocity data obtained from a hot-wire anemometer and its time derivative data were compressed using a compression program running on a Windows PC. Approximated Kolmogorov complexity, AK, and normalized compression distance, NCD, were obtained. With the aid of the AK we can distinguish the complexity within the turbulent region; on the other hand, the intermittency factor cannot. The AK distribution of fluctuating velocity and that of time derivative are similar, and this suggests the similarity in the differentiation of complexity.

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Mean velocity profile in the turbulent boundary layer is studied by using the PDF equation of velocity fluctuations. In the overlap region, following the experimental observation that the PDF of stream wise velocity fluctuations has a self-similar profile, the relation between mean and turbulent intensities are derived. We confirmed the reliability of this equation in comparison with the turbulent intensity distribution derived from the attached eddy model in high Reynolds number flow.

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Contributions of large-scale structures on turbulent statistics in high-Reynolds number channel flows were investigated by means of DNS database. The effects of large-scale structures were observed both in the visualization and transport equation of turbulent kinetic energy. Not only turbulent kinetic energy production but also turbulent kinetic energy fluxes have the second peaks on the log-layer. In RANS by means of Nagano and Shimada model, mean velocity profiles were good agreements with DNS results, turbulent kinetic energy fluxes were considerably disagreed with them. Therefore, turbulent kinetic energy profiles show the tendency of underestimation with increasing of Re.

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Direct numerical simulation of a fully developed turbulent channel flow has been carried out in order to examine the large-scale coherent structures. A 12th order accurate finite difference method in the stream and spanwise directions, and a second-order method in the wall-normal direction is used as special discretization methods. The Reynolds number based on the friction velocity and the channel half width are 2000, 4000 and 8000 The DNS results suggest that the intermediately-streamwise vortexes are existed in between buffer layer and outer later characterized in spanwise direction as 100 wall units and a channel half length, respectively.

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Direct numerical simulation (DNS) of transcritical heated turbulent boundary layers on a zero-pressure-gradient flat plate at supercritical pressures is conducted by using a numerical strategy that is robust and high-order accurate for enabling to simulate the transcritical flows with abrupt variations in thermodynamic properties due to the strong real fluid effects. To the best of my knowledge, the present DNS is the first DNS of zero-pressure-gradient flat-plate turbulent boundary layer under transcritical conditions. The unique and interesting interactions between the real fluid effects at the transcritical conditions and wall turbulence, and their turbulence statistics, which have never been seen in the ideal-fluid turbulent boundary layers, are discussed.

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The SGS mode] in LES is estimated by neural network, which is one of the methods in machine learning. Training data for learning are obtained by direct numerical simulation of turbulent channel flow with various Reynolds numbers. We use velocity gradient tensors and distance from the wall as inputs aiming at improving conventional SGS model. High correlation coefficients are obtained between SGS stress tensors by DNS and those by neural network model.

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PIV measurements of flows near the wall roughness have been carried out. The flow is induced by the concentric cylinder, which consists of rotating inner cylinder and stationary outer cylinder. The inner rotating cylinder has the regularly distributed semi-spherical roughness on the surface. Flow construction, such as longitudinal vortices, low-velocity region in the wake, and high-velocity linear region corresponding to the vortices were clarified by the PIV measurements. From the measured velocity distribution, a simple estimation equation for the flow resistance was proposed. The validity of this proposed equation was confirmed by comparing with the friction measured directly by torque of the inner cylinder.

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A flat plate wing was applied to flow management of the stronger wall jet with constant velocity ratio of U_m/U_e = 4.0 in a self-preserving development. Modifications in turbulent vorticity diffusion process were investigated concerning with suppression of the evolution of the shear layer and entrainment. Measurement of the fluctuating velocity and vorticity correlation has been carried with 4-wire vorticity probe. It is expected that the three-dimensional outer layer manipulator contributes to keep convex profile of the mean velocity, namely, reduction of the turbulent diffusion and enhancement of the vortex stretching.

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Many piping rupture accidents are caused by flow accelerated corrosion (FAC) in nuclear energy power plants. For safety operation, it is important to reveal mechanism of wall thinning phenomena due to FAC. However, it is not perfectly achieved because FAC is complicated phenomena, that relates not only material but also fluid flow behavior. From the view point of hydrodynamics, one of the most important parameter of FAC is mass transfer rate. It is known that the fluctuation of velocity near the wall affects the mass transfer rate. Furthermore, the mass transfer fluctuation is related to small eddies over the pipe surface. In this paper, we try to visualize the pipe flow by tomographic PIV. Changing the particle density, we check the measurement quality to compare the flow field by stereo PIV and numerical simulation.

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Management of rough-wall turbulent boundary layer with LEBU has been investigated experimentally. The flat wing was located at two different heights, h = 0.4δ and 0.8δ. The mean velocity and the streamwise turbulent intensity were measured by the constant temperature type hot-wire anemometer. The LEBU manipulator successfully reduces evolution of momentum thickness and local wall shear stress over rough surface. Reduction of the local skin friction coefficient is greater than that in smooth wall boundary layers. Especially, in case of LEBU located at h = 0.4δ, large drag reduction is maintained for relatively long downstream distance. Reynolds shear stress is significantly reduced by the LEBU manipulator. Reduction of the Reynolds shear stress near the wall is remarkable in the case of h = 0.4δ.

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Many studies on the flow field around an unsteady rigid airfoil in a low Reynolds number regime have been reported. In recent years, the flow field around a moving elastic body, such as the wing of flying insects or the tail fins of water-base life forms swimming through fluids, has become a focus of attention, and its effects are beginning to be understood. In this study, we focused on the flow field around a pitching elastic thin film with low aspect ratio and performed a fluid-structure interaction analysis using ANSYS 14.5/ANSYS-CFX 14.5. We visualized an interaction of vortices shed from leading edge and wing tip on the elastic thin film. The interaction of vortices induce a fast flow in the wake and generates high thrust acting on the thin film.

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The purpose of the present paper is to study the flow structure induced by a combined type of actuator system which is composed of a synthetic jet and fixed vortex generator. The vortex structure downstream of the combined actuator was measured by a scanning stereo-scopic particle image velocimetry(SSPIV). An experiment was conducted in the two-dimensional channel flow with the aspect ratio of 12 and channel height of 10 mm where Reynolds number is 1300. Orifice diameter of synthetic jet is 1.0 mm and Stokes number based on the operation condition is 6.3-12.7. Non-dimensional stroke length is 2.7-16. Then, it is found that strong interaction between the two vortices introduces an effective vortex structure for flow control of the near-wall flow.

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In this study, investigation of development turbulent spots and patches in the transitional two-dimensional channel flow was performed by means of a moving camera that follows the flow at the bulk velocity. The flow visualization of the transitional flow made with flak particle revealed that the patch patterns are consistent and that the phase velocity of the streak structure has faster than that of the patch patterns. Both velocities are faster than the bulk velocity and slightly decrease with increasing the Reynolds number. The decreasing tendency of the velocity and the patch pattern consistency are in qualitative agreement with results of the DNS.

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It is important to understand and control the wake structure behind three dimensional bluff bodies. The purpose of this study is to investigate the effect of velocity disturbances on the wake structure behind a circular disk. The plasma jet generated by a dielectric barrier discharge (DBD) was used as a velocity disturbance. Mean velocity components of streamwise, circumferential and radial direction were measured by X-type hot wire probes. The obtained effects of DBD plasma jet for flow control, the streamwise velocity was increased and the circumferential velocity was decreased.

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Though a lot of researches on boundary layers around a moving body have been conducted, not only details of growing process of vortices but also relation between moving wall and vortices in the boundary layers are not clarified. In this study, the growing process of vortices near moving wall is explored numerically in case of heaving and elastic thin airfoil during one cycle Re=4,000 and St=0.36. As a result, the followings have been clarified in comparison between the rigid and elastic thin airfoils. The vorticity Z and -∂u/∂y have similar time development profile during one cycle at each location of the chord though these increase toward the trailing edge exclusive of the trailing edge. The vorticity Z near the wall is dominated by -∂u/∂y.

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One of the disadvantages of Electric Vehicle (EV) motors is heat removal. Thermo-fluid characteristics in EV motors are, however, not clarified completely. The aim of the present study is to clarify thermo-fluid characteristics in the narrow gap between a pair of coaxial cylinders consisting of the outer one fixed and the inner one rotating. The flow behavior in slits between the rotor and stator is measured via the PIY with fluorescent particles distributed in the water, and is computed via the numerical simulation. We then compared the relationship between the Nusselt number and Taylor number obtained by numerical analysis, with the conventional formula obtained the experimental result.

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In this study, we implement a vortex method based on Object-Oriented Programming using Modern Fortran, well-known as Fortran 2003. Object-Oriented Programming features enable us to maintain, reuse and extend existing program source codes easier. First of all, we implement Doubly Linked List and related procedures including iterator and dynamic cast to store and refer data of vortex elements, which discretize the vortical field of flows. We implement a vortex blob method and apply the method to simulate a plane mixing layer to confirm its suitability. Implementation processes we performed are easier than and resultant source codes we created are simpler than those which are performed and are created through the procedural programming which is popularly used on the programming of numerical simulation methods, confirming the Object-Oriented Programming's suitability for the numerical simulation methods including the vortex blob method.

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The cyclic vortex rings, which are generated cyclically by a pulsating jet, appear to be an effective method for particles and fluids transport. The effect of the formation conditions of cyclic vortex rings such as the velocity amplitude, period and acceleration of jet pulsation conditions, and conditions of an intermittent period, on the axis symmetry characteristics of behavior of vortex rings is investigated experimentally. The results indicate that the axis symmetry characteristics of cyclic vortex rings begin to decay by the following four factors, the influence of a separation vortex ring, the influence of trailing vortex rings, the influence of a previous cyclic vortex ring and the influence of trailing vortex rings. The strength of these decay inducing factors varies with the formation conditions of cyclic vortex rings. The behavior of cyclic vortex rings is determined by the combination and individual strength of decay factors.

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This paper details experimental and studies on the secondary flow losses generated in highly loaded LPT (Low-Pressure Turbine) cascades. Secondary flow loss in LPT significantly contributes to its overall loss, especially in increased stage loading and high-lift airfoil cases. Hence it becomes more important to reduce the secondary flow loss. In the present study, we focus on the effects of load distributions on the secondary flow loss in the highly loaded turbine blade as a method of loss reduction. Detailed experiments are carried out in the cascade outlet endwall region using a 5-hole pressure probe.

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This paper details experimental studies on how the purge air affects secondary flow structure on the contoured endwall using a rotating test rig. Secondary flow loss in low pressure turbine significantly contributes to its overall loss, especially in increased injection purge air cases. Hence it becomes more important to reduce the secondary flow loss. In the present study, we focus on the effects of purge air on the secondary flow structure in the endwall contouring. Detailed experiments are carried out in the rotor outlet using a 5-hole pressure probe.

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In an automotive turbocharger development, a wide range turbine performance data is required for a precise of an engine matching with a turbocharger. In order to obtain a wide range turbine performance accurately, a wide range operation procedure was introduced in this study by controlling a compressor power which is installed coaxially with a turbine. A variable inlet guide vane which was set on a compressor and could adjust a compressor Euler head and also varying a compressor inlet pressure could adjust a compressor mass flow rate. Applying these procedures, it was confirmed experimentally that a turbine operating range was enhanced more than twice of an ordinal procedure.

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The new type of diffuser augmented wind turbine (DAWT) called "wind-lens turbine" has been developed. The wind-lens turbine has a diffuser with brim called "wind-lens", by which the wind concentration on the turbine rotor and the significant enhancement of the turbine output can be achieved. A wind-lens turbine which has the higher output power coefficient than the Betz limit and other DAWTs has been developed. The reasons that the wind-lens turbine achieved higher output power coefficient than those of others are the wind-lens turbine was designed with the appropriately estimated wind velocity at the rotor inlet and the optimization method has been applied to the aerodynamic design of the wind-lens turbine.

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This study deals with an inhibitory effects of partially shrouded blade tip on the tip leakage flow in a compressor linear cascade. The airfoils representative of a typical rotor blade used in the rear stages of high pressure axial compressors. Reynolds-Averaged Navier-Stokes simulations have been conducted for three shrouded blade tips (0-0.6Cx, 0.2-0.8Cx and 0.4-1.0Cx installed). Numerical results showed the case of 0-0.6Cx, 0.2-0.8Cx shrouded blade tips could effectively reduce both the loss of the tip region and the overall loss.

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In this study, effects of the flow path height at the impeller exit and the diffuser on flow fields in a transonic centrifugal compressor have been investigated. The detached-eddy simulation (DES) was applied to investigate the change of flow fields when the flow path height was reduced. The simulation revealed that the reduction of flow path height affected behavior of the tip leakage vortex. The suppression of tip leakage vortex breakdown led to the reduction of not only the accumulation of low momentum fluids at the impeller exit but the reversed flows in the impeller and the diffuser.

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Large eddy simulation of internal flow of a centrifugal blower was performed in order to analyze the rotating stall at a partial flow rate. The blower has 12 impeller blades and vaneless diffuser with a scroll. Numerical results were validated by comparisons with measurements in terms of static head, velocity distribution at the impeller outlet and propagating speed of a stall cell. Propagating speed of the stall cell are about 70% of impeller rotational speed in both the experiment and numerical computation.

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The cause of pressure fluctuation occurred in a multi-stage centrifugal blower with inlet guide vane (IGV) under the partially opening condition of IGV was investigated using the system dynamics calculation based on the lumped parameter model. This pressure fluctuation occurred in the flowrate region where the slope of total static pressure-rise characteristic curve was steeply negative and total system seemed to be stable, hi our previous study, this pressure fluctuation was considered to be the mild surge that was caused by the stability balance between the first stage and the second to last stage. The system dynamics calculations could reproduce the mild surge behavior in the system and we confirmed that this pressure fluctuation was certainly the mild surge.

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It is required that the stall control in the impeller and/or diffuser of the centrifugal fen and compressor for operating range expansion. Particularly in the open impeller, it is considered that tip leakage flow which occurs between impeller tips and casing shroud causes loss and stall which affect at performance of centrifugal fan and compressor. In this study, for open impeller of centrifugal fan, we performed unsteady numerical analysis and examined the influence of tip leakage flow on the stall of an impeller at low flow rate.

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In the previous development of the packaged air conditioner, the pressure-loss was estimated based on the flow field of simplified channels for reduction of the fan power of the indoor unit. However, it is important that the flow field in actual flow channels is considered in order to improve the performance. In this study, we developed the total integrated simulation technology for visualizing actual flow fields in the indoor unit with Computational Fluid Dynamics. It was found that the flow field around the fan was complex by the Heat Exchanger (HE). The velocity distribution at the center of the inside of HE depends on the difference of inflow angles. There is the area of the inflow angle distribution of 10 degrees or less at the center in the height direction of HE. The velocity distribution causes the increase in the pressure loss and the decrease in the efficiency of heat exchange cycle.

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Recently, fans have been used in order to cool the interior of electronic equipment. Especially the sirocco fan has been used in a narrow place. There is an advantage that it can reduce the production cost of the sirocco fan if it has a small number of blades. However, there is little knowledge regarding the sirocco fan with a small number of blades. In order to clarify the internal flow of the sirocco fan with a small number of blades, the LES (Large Eddy Simulation) was conducted. As a result of the LES, it was acquired that pressure fluctuation between the blades becomes especially large in θ=250deg〜315deg at the high flow rate points (Q=0.0239m^3/s, Q=0.0178m^3/s). Moreover, in θ=0deg〜180deg, there are no significant pressure fluctuations between the blades at the high and low flow rate points (Q=0.0239m^3/s, Q=0.0178m^3/s, Q=0.0076m^3/s).

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The authors experimentally try to appear the characteristics of the flow inside a cross-flow fan. By the running-average technique, the authors reveal the features in pressure wave form. By comparing the distributions for the singular aspect ratio L/D_2 = 0.6 with those for L/D_2 = 0.3 and 1.0, the authors reveal that the radial position of an eccentric-vortex center becomes inward with decreasing L/D_2. The authors confirm the minimum-pressure coefficient C_<pmin> which is a reduced minimum pressure defind by p_<min>/0.5pu_2^2 is independent of Re not only qualitatively but also quantitatively. The authors get such a conclusion as the eccentric-vortex strength is independent of Re, in addition to the conclusion that the eccentric-vortex centre moves to the impeller centre with decreasing L/D_2. Strictly speaking, C_<pmin> tends to decrease with decreasing Re for L/D_2 = 0.3 and 0.6. This tendency is converse for L/D_2 = 1.0.

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In order to improve efficiency of propeller fan which are used in air-conditioner, the dominant flow structure of the propeller fan, tip vortex was studied by visualization method. The tip vortex was visualized from inlet side and outlet side. The visualization results show that the tip vortex has strong vortex core in its center, which likes the eye of typhoon. The vortex core is very clear when tip vortex is in inlet region, but it becomes not clear when it is in outlet region. It is also observed in outlet region that the size of tip vortex along radial direction is larger than one third of fan blade span. And the present study clarifies the trajectory of tip vortex center from leading edge tip side to outlet side near the trailing edge tip of next blade.

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The system requirements of axial flow fans are various. It is often seen that the axial flow fans are used under the inadequate operating condition. In recent downsizing equipment design, the cases where some obstacles installed in upstream of fans for device densification are increasing. In the present study, an attempt is made to clarify the influence of an upstream obstacle on the performance characteristics of axial flow fan. Furthermore, the flow instabilities around the fan with the obstacle are discussed.

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Numerical simulations were conducted by using LES (Large Eddy Simulation) with DSM (Dynamic Smagorinsky Model) about the axial flow small fan for cooling electronic devices. In this study, the tested fan has grid for turbulence located in the suction side. Using three type of grid for turbulence were used for study. First has diameter of 3mm and pitch of 15mm(GT3), second has diameter of 4mm and pitch of 20mm(GT4),third has diameter of 1mm and pitch of 5mm(GT1). The flow pattern around the fan blade and RMS of pressure fluctuation on the fan blade surfaces were compared under the three turbulence conditions and no turbulence condition. As a result, it is shown that noise is increased by the grid for turbulence. These cause are considered large pressure fluctuations which were revealed by numerical analysis. We found that pressure fluctuation of leading edge is caused by incidence fluctuation.

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A pressure estimation system using velocity data measured by PIV experiment has been developed and validated for wing wake flow field measurement. The system uses PIV data of three cross-sections in wing wake called a 2.5-Dimensional model. The 2.5D model developed by the authors is better than the 2D model for the wake pressure estimation. In this article, the 2D model and the 2.5D model are compared and some added terms of 2.5D model are picked up and their effects are examined on pressure estimation.

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