Leading Edge Side Research Articles

Tumble Flow Enhancement Applied for Low-Load Condition of Engines by Utilizing Reverse Flow Phenomenon in Intake Port

<div class="section abstract"><div class="htmlview paragraph">We established a technology that can enhance the tumble flow in the cylinder only in a partial load range of the engine without the need to use any intake path switching mechanisms.</div><div class="htmlview paragraph">Firstly, we attempted to understand the basic phenomena of intake flow by using a CFD model, while using a butterfly throttle valve in a straight pipe. By doing this, we were able to observe the reverse flow of intake air that appears after the intake air has passed the throttle valve when the throttle valve opening is 30% or less. This reverse flow is generated mainly in the flow that has passed the trailing edge of the throttle valve. At both sides of the trailing edge opening, the flow is slowed down by diffusing. The flow is then pulled into the low-pressure zone created behind the throttle valve. In addition, a part of the reverse flow merges with the air flowing on the leading-edge side.</div><div class="htmlview paragraph">Next, we confirmed that installing a flow separator behind the throttle valve that vertically divides the flow can successfully capture the reverse flow into one of the two flow paths. Furthermore, we confirmed that optimizing the separator position can capture most of the flow into one path, thereby gaining the required amount of flow that can generate tumble in the combustion chamber.</div><div class="htmlview paragraph">By applying the above results to an actual engine, we validated the effect through a CFD flow analysis and also steady flow tests. As a result, we confirmed that this system can enhance tumble within a partial load range of the engine to a level that is equivalent to that obtained by a tumble port that has a flow path switching mechanism.</div></div>

Unsteady vortex structures in the wake of nonaxisymmetric bumps using spiral MRV

The temporal characteristics of the wake structure behind a nonaxisymmetric bump are studied using spiral magnetic resonance velocimetry (MRV) to measure time-series of all three velocity components in y–z-planes for bump orientations of $$5^\circ$$ , $$10^\circ$$ , $$15^\circ$$ , and $$20^\circ$$ relative to the freestream flow. The mean wake structure was shown previously to be highly sensitive to bump orientation (Ching et al. Exp Fluids, 2018). The spiral MRV method is validated by comparison to the established MRV techniques in a flow with forced periodicity. Measured velocity fluctuations in the bump wake decrease significantly as the bump angle is increased. A quasi-periodic shedding cycle is reconstructed using spectral proper orthogonal decomposition. The reconstructed cycles of each velocity component are matched through a divergence minimization method to examine the structure of the shed vortices. The vortex shed from the trailing edge side of the bump weakens as the bump angle is increased, whereas the vortex shed from the leading edge side maintains its strength. The alternating vortices move across the centerline as they are advected downstream, explaining the common-down vortex pair observed in the far wake mean fields.

Influence of geometric parameters on the thermal hydraulic performance of an ellipsoidal protruded enhanced tube

ABSTRACTIn this paper, the numerical simulation model of an ellipsoidal protruded tube has been established considering thermal hydraulic performance. The flow field characteristics and heat transfer characteristics of an ellipsoidal protruded tube were investigated. Effects of protrusion configuration, depth, pitch, number, axis ratio, and angle on thermal hydraulic performance were discussed using the realizable k–ε model under the steady-state condition. These results show that protrusion volume has a major impact on thermal hydraulic performance. The protrusions make the zone of flows narrow down at the protrusion leading edge side and expand at the trailing edge side, which resulted in protrusions increased turbulence, flow mixing, flow separation, and boundary layer distribution, thus enhancing the heat transfer performance. The maximum of local Nusselt number is located at the protrusions leading edge, and the minimum of local pressure is located at central of the protrusion surface. The configuration has no significant effect on the thermal hydraulic performance. Furthermore, the optimal selection of parameters boosts the heat transfer by up to 130.9% and amplifies the pressure loss up to 103.2%.

風車ブレードの点検・補修ロボットの研究開発アプローチ

In this paper, we introduce a inspection and repair robot system for wind power generating windmill. We propose a robot which hangs a rope from top of a tower of a windmill and rolls up and down the rope to move up and down side on a leading edge side of the blade. Distinguished feature of the robot system is that the robot can contact with a surface of the blade.

Failure Analysis of a Compressor Blade of Gas Turbine Engine

Abstract The stage II compressor stator blade of a developmental gas turbine engine was found damaged during dismantling of the engine after test run. A portion of the blade was found fractured from the hub region at leading edge. A crack was also observed extending from the fractured surface towards the centre of the airfoil region of the blade. Low magnification stereo-binocular observation revealed presence of beach marks on the fractured surface indicating the blade failure in progressive mode. This observation was further confirmed by scanning electron microscopy. The crack origin was at the blade hub-stem junction on the leading edge side. Presence of machining/filing marks appeared to be the reason for the fatigue crack initiation from this region. No metallurgical abnormalities were present at the crack origin. However, deep filing/machining lines were observed at the stem region of the blade attributing to the cause of failure.

Writer Field Gradient Measurement on Spinstand

The gradient of magnetic head field is very critical in the writing process and it is one of the key factors to determine the achievable linear density of magnetic recording system. This work proposed a new method to measure the writer field gradient on Spinstand. The even harmonic ripple effect [4] is used to produce the modulated magnetostatic field at the writing transitions generated from the old data pattern at leading edge side of the writer. The newly written single tone signals have the modulated transition shift. Through the duty cycle measurement of the single tone signals, the delta transition shift can be measured. With the calculated magnetostatic field based on the media magnetic properties and the measured size of writer footprint, the writer field gradient equals the ratio of delta magnetostatic field over delta transition shift.

Flow field analysis inside a gas turbine trailing edge cooling channel under static and rotating conditions

The flow field inside a modern internal cooling channel specifically designed for the trailing edge of gas turbine blades has been experimentally investigated under static and rotating conditions. The passage is characterized by a trapezoidal cross-section of high aspect-ratio and coolant discharge at the blade tip and along the wedge-shaped trailing edge, where seven elongated pedestals are also installed. The tests were performed under engine similar conditions with respect to both Reynolds (Re = 20,000) and Rotation (Ro = 0, 0.23) numbers, while particular care was put in the implementation of proper pressure conditions at the channel exits to allow the comparison between data under static and rotating conditions. The flow velocity was measured by means of 2D and Stereo-PIV techniques applied in the absolute frame of reference. The relative velocity fields were obtained through a pre-processing procedure of the PIV images developed on purpose. Time averaged flow fields inside the stationary and rotating channels are analyzed and compared. A substantial modification of the whole flow behavior due to rotational effects is commented, nevertheless no trace of rotation induced secondary Coriolis vortices has been found because of the progressive flow discharge along the trailing edge. For Ro = 0.23, at the channel inlet the high aspect-ratio of the cross section enhances inviscid flow effects which determine a mass flow redistribution towards the leading edge side. At the trailing edge exits, the distortion of the flow path observed in the channel central portion causes a strong reduction in the dimensions of the 3D separation structures that surround the pedestals.

Effect of beam angle on HAZ, recast and oxide layer characteristics in laser drilling of TBC nickel superalloys

Industrial applications of laser drilling include the production of cooling holes at acute angles in certain parts of the aero-engine components. These parts are often covered with ceramic thermal barrier coatings (TBC) to protect them from reaching excessive temperatures in hot engine environments. Acute angle TBC drilling brings three major simultaneous complications to the process. These are: (i) multi-layer drilling, (ii) non-symmetrical geometry and melt ejection, and (iii) increased depth of drilling. In a previous investigation by the authors, delamination of TBC was found as a main problem of angled drilling and mechanisms involved were studied. In the present study, implications of these difficulties on the hole quality is investigated through a comparative study of vertical and acute angle drilled holes. Characteristics of recast layer, heat-affected zone (HAZ), oxide layer and TBC delamination are investigated. Variation of these metallurgical characteristics with the depth of the hole is evaluated. Results for vertical and inclined holes are compared. The extent of HAZ, recast layer and oxide layer is seen to vary significantly with location and is found increasing with decreasing drilling angle to surface. Numerical simulation of pulsed laser heating of TBC Nimonic 263 was carried out for acute angle drilling with assist gas considerations. Results from the simulation suggested that the total heat transfer rate is higher on the leading edge side than the trailing edge of the heated region. Experimentally observed larger HAZ on leading edge side and larger recast layer on trailing edge side are explained by the analysis of heat flow characteristics obtained with the model.

정사각 막냉각홀 내부에서의 열/물질전달 및 유동 특성 (I) - 분사비 및 레이놀즈 수 효과 -

An experimental study has been conducted to investigate the heat/mass transfer characteristics within a film cooling hole of square cross-section for various blowing ratios and Reynolds numbers. The experiments have been performed using a naphthalene sublimation method and the flow field has been analyzed by numerical calculation using a commercial code. A duct flow enters into a film cooling hole in a cross-direction. For the film cooling hole with square cross-section. it is observed that the reattachment of separated flow and the vortices within the hole enhance considerably the heat/mass transfer around the hole entrance region. The heat/mass transfer on the leading edge side of hole exit region increases as the blowing ratios decrease because the main flow induces a. secondary vortex. Heat/mass transfer patterns within the square film cooling hole are changed little with the various Reynolds numbers.

Heat/Mass Transfer Measurement Within a Film Cooling Hole of Square and Rectangular Cross Section

An experimental study has been conducted to investigate the heat/mass transfer characteristics within film cooling holes of square and rectangular cross section. The experiments for this study have been performed using a naphthalene sublimation method, and the flow field has been analyzed by numerical calculation using a commercial code (FLUENT). The rectangular cross section has the aspect ratio of 2 and the same hydraulic diameter as the square cross section. A duct flow enters into a film cooling hole in a cross direction. For the film cooling hole with square cross section, it is observed that the reattachment of separated flow and the vortices within the hole enhance considerably the heat/mass transfer around the hole entrance region. The heat/mass transfer on the leading edge side of hole exit region increases as the blowing rates decrease because the mainflow induces a secondary vortex. Heat/mass transfer patterns within the film cooling hole are changed slightly with the various Reynolds numbers. For the film cooling hole with rectangular cross section, overall heat/mass transfer characteristics are similar with those for the square cross section. However, heat/mass transfer on the leading edge side of hole entrance region has two peak regions due to split flow reattachment, and heat/mass transfer on the leading edge side of hole exit region is less sensitive to the blowing ratios than the square cross-sectional case.

New technologies for electrical testing: PWB cost impact

While PWB selling prices keep on decreasing at the average rate of 6 percent per year, the cost of advanced electrical testing is escalating in a dangerous way. Today, investing in a new test capacity has become one of the most strategic decision for a PCB manufacturer, and not only on the leading edge side. This paper will investigate what will be the impact of emerging test technologies on the cost of manufacturing tomorrow’s PWBs.

Stall Margin Improvements of Conventional Axial Flow Fans with the Reformed Casingtreatments.

At the first part of this paper, the experiments and results to the blowing and suction on a fan are presented, and it is found that blowing toward the down stream direction are more effective and blowing location is suitable on the leading edge side of blades. On basis of these results, the reformed casingtreatments which the blowing air from the slots makes the large relative momentum for blade chord are build, and the experiments using the two conventional fans equiped with the reformed casingtreatment and conventional one are performed. So, the very large stall margin improvements (about 1.7 times) and about 0.5% efficiency penalty of 10% stall margin improvement at design flow rate are obtained for the reformed casingtreatment.

Effects of tip clearance on the noise generated from low pressure axial flow fans. Difference caused by the width and location of a ring set in the tip clearance and the blade tip profile.

The effect of the width and the location of a ring set in the clearance between a duct inner wall and a blade tip and the profile of a blade tip on fan noise are experimentally investigated by using three rings of different widths and four impellers with different tip geometry. The results are summarized as follows : A considerable amount of noise reduction can be expected by setting a ring within a tip clearance, when its initial gap is rather large. Both the noise and the aerodynamic characteristics at the maximum efficiency point are better in the case with a larger gap on the leading edge side than on the trailing edge side. In the lower flow rate range, however, the fan with a smaller tip clearance on the leading edge side is superior.