Row Of Holes Research Articles

Structural Optimization and Application Research of Alkali-Activated Slag Ceramsite Compound Insulation Block Based on Finite Element Method

The research and application of new wall materials have been attracting increasing attention owing to the continuous promotion of sustainable development in the building industry. An alkali-activated slag ceramsite compound insulation block (AASCCIB) is used as the research object. Based on the finite element method, the effects of different numbers of hole rows and hole ratios on the thermal and mechanical performances of AASCCIBs are analyzed using ANSYS CFX. On this basis, the AASCCIB with the optimal comprehensive performance is determined by a multi-objective optimization analysis. Finally, the improvement effect of the AASCCIB wall on the indoor thermal environment relative to an ordinary block (OB) wall is quantitatively analyzed using ANSYS CFX. The results show that the von Mises equivalent stress and heat transfer coefficient of the AASCCIB decrease with the increase in the hole ratio when the hole shape and number of hole rows are constant. AASCCIB B1 has the optimal comprehensive performance among six AASCCIBs, with the heat transfer coefficient and average von Mises equivalent stress of 0.446 W/(m2∙K) and 9.52 MPa, respectively. Compared with the indoor lowest and average temperatures of the building with the OB wall, those of the building with the AASCCIB wall increased by at least 1.39 and 0.82 °C on the winter solstice, respectively. The indoor temperature difference decreased by at least 0.83 °C. In addition, the indoor highest temperature, average temperature, and temperature difference decreased by at least 1.75, 0.79, and 1.89 °C on the summer solstice, respectively.

Scaling criteria accuracy for turbine blade film cooling effectiveness at unmatched temperature ratio conditions

• The suitable criteria for film cooling effectiveness scaling at unmatched temperature ratio conditions are obtained. • Reasons leading to the scaling deviation are analyzed. • The influence of temperature ratio on film cooling effectiveness is investigated. Cooling performance experiments for turbine blades are increasingly being conducted at low temperature and pressure in order to reduce the cost and difficulty of the experiments. However, the lack of similarity between scaling and real engine conditions leads to deviations in the experimental results. The application of a suitable scaling criterion can significantly reduce this deviation and promote the engineering of scaling experiments. This study explores a suitable criterion for scaling of film cooling when the coolant to mainstream temperature ratio for scaling conditions deviates from the datum condition, taking the 1st stage stator from the E 3 aero engine as an example. This study focuses on the pressure side of the blade. The effect of the coolant to mainstream temperature ratio on the pressure side film cooling effectiveness was initially investigated based on both numerical and experimental methods. The scaling accuracy of six criteria was then compared based on numerical results, followed by an analysis of the reason leading to the scaling deviation. In our study the datum condition was selected to have an inlet pressure and inlet temperature of 1861 kPa and 1543 K, respectively. This operating condition corresponds to that of a real engine. Finally, the results obtained from the numerical method are validated experimentally. Both the numerical and experimental results indicate that the film cooling effectiveness on the pressure side decreases with an increase in the temperature ratio at low temperature ratio conditions, while the trend reverses at relatively high temperature ratio conditions. We found that the M criterion is suitable for scaling the downstream region of −60 % l/l 0 (the downstream region of the last cooling hole row), while the most accurate scaling results in the region from the leading edge to −60 % l/l 0 (the region with dense film cooling holes) can be obtained by applying the I criterion. The region near the leading edge (around cooling hole row 1) is difficult to scale. This is because the separation in the downstream region of cooling hole row 1 in the datum condition does not exist in any scaling condition.

Equation of hole arrangement for concrete beam demolition using soundless chemical demolition agent

Soundless chemical demolition agents (SCDAs) provide a reliable alternative for demolishing concrete structures in densely populated areas. However, research on the demolition of reinforced concrete member using SCDAs has not been conducted in detail. In this study, 12 concrete beam segments with different parameters were prepared to investigate the method of demolishing concrete beam using SCDAs. The arrangement of single row holes perpendicular to the upper surface of the beam segment was adopted, and the stirrups at the top of the beam segment were cut off along the hole connecting line and its extension line before grouting. The results showed that owing to the defect caused by cutting stirrups, the crack on the upper surface of the beam segment developed at the cutting seam, and the vertical crack on the end surface of the beam segment was also formed at the cutting seam and extended to the bottom of the beam segment. Besides, the average volume expansion rate of SCDAs in all boreholes in the beam segment (i.e. volume expansion rate of SCDAs) was determined to evaluate the impacts of the concrete compressive strength, hole spacing, and hole diameter on the crushing effect. Finally, a new equation for computing the hole spacing was derived, considering the time after grouting, concrete compressive strength, hole diameter, tie reinforcement ratio, ambient temperature, and volume expansion rate of SCDAs. The solution obtained using the proposed equation was in good agreement with the experimental results and was expected to provide guidance for the engineering application of SCDAs.

Experimental study on thermo-hydraulic performance of a solar air heater with rectangular perforated duct inserts

This paper examines the results of experiments conducted on a glazed solar air heater duct which is modified with an additional rectangular duct insert having perforation on its top surface. This modified rectangular duct of varying height is designed to split the incoming air into the absorber. This is presumed to create a pressure difference above and below the perforated surface that will enhance the convective heat transfer due to the cross-flow effect. It is observed from the experiments that the drop in pressure along the absorber passage decreases with an increase in the height, increase in hole diameter, and the number of rows of the hole. It is established from the experiments that thermal efficiency is found to be maximum for the height ratio (h/H) of 0.66 when compared to height ratios of 0.50 and 0.83, perforated duct inserts. Further, by varying the hole diameter ratio and the number of rows, it is noted that two rows of holes with hole diameter ratio of 0.096 configuration gives the maximum thermal efficiency of 84.8% and thermo-hydraulic efficiency of 81.06%.

An experimental study of the thermal behavior of bricks integrated with PCM-capsules in building walls

Buildings are the major energy users and by 2035, they will be the fourth largest source of greenhouse gas emissions. Phase change materials (PCMs) are applied to shift the peak-load to the off-peak-load, positively effecting the efficiency of the building. In this paper, an experimental embedding of PCM (Paraffin) with bricks in conventional wall layers is carried out. The effect of this on the thermal diffusion of the inner surface of the wall is studied. Capsules are manufactured to fit the size of the holes inside the bricks and they are filled with Paraffin (147 kJ/kg latent heat, 38oC solidified and 43oC liquidised) and closed in a way that prevents leakage. Each brick contained two rows of holes (5 holes per row). Capsules are placed in the holes at a rate of 5 capsules per brick and 10 capsules per brick. Three wall samples are experimentally tested: traditional wall, wall containing 5 capsules/brick and a wall containing 10 capsules/brick. The indoor test with light intensity has been fixed on 900 W/m2 during the heating period for 4 hours and the remaining period of cooling. The temperature measured and recorded for the internal, external surfaces and the middle of the wall using K-type thermocouples and datalogger. The results indicated that, bricks wall with 10 PCM- capsules per brick reduced the heat flux by 34.17% compared with traditional wall sample, and energy stored 50% more than a wall with 5PCM-capsules per brick. The lowest temperature of the internal wall surface of sample 10 capsules per brick is recorded compared to the reference wall where the difference is more than 3°C.

Remark on Justification of Asymptotics of Spectra of Cylindrical Waveguides with Periodic Singular Perturbations of Boundary and Coefficients

To perform an asymptotic analysis of spectra of singularly perturbed periodic waveguides, it is required to estimate remainders of asymptotic expansions of eigenvalues of a model problem on the periodicity cell uniformly with respect to the Floquet parameter. We propose two approaches to this problem. The first is based on the max–min principle and is sufficiently easily realized, but has a restricted application area. The second is more universal, but technically complex since it is required to prove the unique solvability of the problem on the cell for some value of the spectral parameter and the Floquet parameter in a nonempty closed segment, which is verified by constructing an almost inverse operator of the operator of an inhomogeneous model problem in variational setting. We consider boundary value problems on the simplest periodicity cell: a rectangle with a row of fine holes.

Playing marbles, playing music

Playing marbles, playing music

Guiding light in two-dimensional photonic crystal slabs

This work uses the Guided-Mode Expansion method to calculate the photonic band structure and the quality factor for a photonic slab comprising a hexagonal lattice of air holes embedded in a semiconducting material. We consider that the dielectric constant of the semiconductor changes with pressure at a fixed temperature. Using the supercell technique, we removed a row of air holes from the slab to obtain a confined waveguide whose frequency increases with pressure. However, the quality factor decreases with the increase in the applied pressure.

Experimental research on film cooling characteristics of multi-film-hole-rows

The present study experimentally explores the effect of the film-hole-row layout and hole angle on the film cooling characteristics of the multi-rows of micro-film-hole by the transient infrared technique. Reynolds number based on the diameter of the micro film hole and Knudsen number are 7000 and 7 × 10−5, respectively, and the dimensionless parameters of the experiment are the same as those of the real turbine blade. Two blowing ratios of 0.5 and 1.0 are investigated. Five rows of the film hole in leading edge have a pronouncedly positive effect on the film cooling effectiveness in the upstream region, and obtain an excellent coolant coverage at the blowing ratio of 1.0. The Nusselt number of the whole test surface is significantly decreased by five rows of the film hole in leading edge with the hole angle of 45° at the blowing ratio of 1.0. Increasing the hole angle from 45° to 90° decreases the span-wise averaged film cooling effectiveness of the test surface, and this phenomenon is obvious at the blowing ratio of 1.0, the maximum is about 29 %. There is a high heat transfer region at the beginning of the test surface of the five rows of the film hole in leading edge with the hole angle of 90° structure due to the mainstream-blockage-effect.

Injection in Boundary Layer and Its Influence on Heat Transfer.(Dept.M)

An experimental investigation was performed to examine the effect of film cooling from different shape holes at the leading edge of a flat plate. The interaction of a heated jet with a deflecting flow has been performed. The secondary flow is introduced at different angles to the mainstream flow direction with single row of holes. Visualization studies using yarn tufts are reported. The influences of hole geometry; mainstream boundary layer thickness are described significant improvements in the film cooling effectiveness are observed by having the coolant and passages widened before the exit of the secondary fluid. Normal-inclined injection gives superior results.

Karstification Problems in the Haditha Dam, West Iraq

Haditha Dam is constructed on the Euphrates River in the western part of Iraq completed in 1988 and located 14 km west of Haditha town. Haditha Dam is a combined earthfill and concrete dam with a total length of 9064 m. The maximum height of the dam is 57 m from the deepest point at the river channel and dam crest level is 154.00 m (a.s.l.). The storage capacity is 6×109 m3 at normal operation water level of 143 m (a.s.l.). The exposed formations in the dam site and reservoir area are the Euphrates (Lower Miocene) and Fatha (Middle Miocene) formations. Both formations are well known in Iraq to be karstified at different intensities. The right bank of the Euphrates River is severely karstified with tens of sinkholes of different shapes, dimensions and activities. The presence of the karstified rocks is the main reason the dam has a very long grout curtain which extends along its entire length and includes the concrete powerhouse and spillway structure in the river channel, and the right and left bank extensions. The right bank extension of the grout curtain is exceptionally long due to the extent of the sinkhole area. Grouting was performed here in boreholes drilled at one-meter spacing to reduce water penetration and movement through the flank of the dam. The grout curtain under the embankment in the river section was done in two rows, while under the concrete structure it is comprised of three rows of holes. The left bank extension has two rows. The depths of all parts of the curtain varied following the karstification zones and intensities. The main aim of the current study is to elucidate and discuss the influence of the karstified rocks at the dam site and reservoir on the design and especially the length of the dam and the need for side extensions.

Effect of microchannel on combined impingement and film cooling of a concave surface

In this work, a micro-channel-based wall cooling approach is investigated. The cooling efficiency of curved surfaces is determined by employing a computational study for conjugate heat transfer. A semi-circular curved body depicting the turbine blade leading edge, with a microchannel placed in the solid wall of the body and three rows of film holes, is considered for the study. The film holes are positioned along a stagnation line and either side of the stagnation line at an angle of 25o. The steady-state solver with a realizable k-ε turbulence model is used to study the heat transfer results for film cooling in a 3D geometry. Simulations were carried out, and subsequently, parametric analysis was performed to observe the effect of varying blowing ratio and temperature ratio. The temperature distribution is observed to be more uniform due to the presence of the microchannel, resulting in a lesser thermal gradient on the curved surface. It is also noted that overall effectiveness increases with the blowing ratio. The maximum increase in overall effectiveness due to placing the microchannel is found to be ~16% for the blowing ratio of three.

Film Cooling Superposition Theory for Multiple Rows of Cooling Holes With Multiple Coolant Temperatures

Abstract The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass. The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7–7–7 cooling holes were first evaluated with a single coolant temperature to demonstrate that classical superposition theory applies well to the present configuration. Superposition theory is then extended to the context of multiple coolant temperatures and a new nondimensional parameter is identified, which governs cooling performance. The theory is experimentally evaluated by independently varying the coolant temperatures of the two rows. Circumstances are identified in which the second row of cooling holes may be detrimental to cooling performance.

Hole arrangement effect to film cooling performance on leading edge region of rotating blade

The effect of relative position of two rows of film holes on film cooling performance was experimentally and numerically investigated on each side (suction side and pressure side) of rotating blade leading edge. The film cooling performance was measured by pressure sensitive paint and phase-locked techniques. The numerical simulation was also employed to improve the understanding of flow filed. The first row of film holes is fixed at α1 = ±10° downstream of stagnation line and is followed by the second row of holes with staggered arrangement. The span-wise relative positions between two rows of holes, P2/P1, are ranged from 1/4 to 3/4. Meanwhile, the stream-wise location of second row of holes is varied from α2 = ±25° to ±40°. Five blowing ratios ranged from 0.5 to 2.0 are also employed. The results indicate that the effect of relative position of two rows on film cooling is different on the two sides of leading edge. On the suction side, the relative position between two rows of holes significantly affects the interaction between the adjacent jets from two rows, which determines the distribution and value of film cooling effectiveness. When it comes to the leading edge pressure side, closer distance between two adjacent holes in two rows produces better film cooling performance. Meanwhile, the effect of relative position between two rows of holes is mainly located in the near hole region.

Experimental study on film cooling and heat transfer characteristics of a twisted vane with staggered counter-inclined film-hole and laid-back-shaped-hole

The present study first proposes the counter-inclined film-hole with the staggered arrangement applied on the vane leading edge. The film cooling effectiveness (η) distribution of a twisted vane with the new cooling scheme of the leading edge and laid-back-shaped-holes is measured by the pressure Sensitive Paint (PSP) technique in a fan-shaped wind tunnel. The transient Thermochromic Liquid Crystal (TLC) technique is used to measure the heat transfer coefficient (h). The effects of density ratios and mass flow ratios (blowing ratios) are studied. The experiments are carried out at four mass flow ratios 12%, 9%, 8%, and 7.5% and three density ratios 1.0, 1.5, and 2.0. The pressure in the mid-span of the vane is measured to understand the η and h distributions. The results indicate that the increase rate of the span-wise averaged η upstream of the pressure surface is more prominent with the density ratio increasing from 1.0 to 1.5, and the maximum is about 86.9%; whereas increasing the density ratio from 1.5 to 2.0 significantly improves the span-wise averaged η of the suction surface. Increasing mass flow rates of the trailing and leading cavities has positive effects on the η of the whole vane surface except for the leading edge near the end wall at the density ratio 1.5; whereas it only increases the η on the pressure surface at the density ratio 1. Increasing the mass flow ratio of the leading cavity from 7% to 10% increases the h ratio of the whole cane, and it enlarges the high h ratio of leading edge the mid-chord regions at the suction side. The span-wise averaged heat flux ratio in the region between film hole rows at the density ratio 1.5 is lower than that at the density ratio 1.

Optimization design in perforated AL-CFRP hybrid tubes under axial quasi-static loading

Induced structure has been widely used in thin-walled structures to reduce the initial peak crash force (PCF) and improve the crashworthiness. In this paper, the perforated aluminum-carbon fiber reinforced polymer thin-walled tube (AL-CFRP tube) was investigated to explore the design issue of the parameters of induced holes. For the purpose, firstly, a finite element model of perforated AL-CFRP tube was established and verified with experiments. Secondly, under the condition of single factor, the effects of different diameter, number and number of rows of induced holes on the AL-CFRP tube were studied respectively. Finally, the response surface method (RSM) was used to analyze the influence of the parameters of the induced holes on the total energy absorption (EA) and initial PCF values of perforated AL-CFRP tube. The non-dominated sorting genetic algorithm II (NSGA-II) was used to seek the optimal combination of the parameters of induced holes. The results demonstrate that the induced holes structure can effectively improve the crashworthiness of AL-CFRP tube, when the parameters of induced holes are a row of holes with a diameter of 5 mm and a number of 4, the PCF can be reduced by 17.43% and the crush force efficiency (CFE) can be increased by 20% without weakening the total EA.

Experimental Study on Film Cooling Effectiveness of Blade With Chevron-Shaped Holes Under Wake Influence

Abstract Gas turbines have been widely used. With the continuous improvement of the performance of gas turbines, the turbine inlet temperature has greatly exceeded the heat-resistance limit of the turbine blade material, so advanced cooling technology is required. The film cooling effectiveness distribution over the blade under the effect of wake was obtained by the pressure-sensitive paint (PSP) technique. The test blade has five rows of chevron film holes on the pressure side, three rows of cylindrical film holes on the leading edge, and three rows of chevron film holes on the suction side. The mainstream Reynolds number is 130,000 based on the blade chord length, and the mainstream turbulence intensity is 2.7%. The upstream wake was simulated by the spoken-wheel type wake generator. The film cooling effectiveness was measured at three wake Strouhal numbers (0, 0.12, and 0.36) and three mass flux ratios (MFR1, MFR2, and MFR3). The results show that the increase of mass flux ratio leads to a decrease of the film cooling effectiveness on the suction surface. In the wake condition, the effect of mass flux ratio is weakened. Wake leads to a marked decrease of the film cooling effectiveness over most blade surface except for the surface near leading edge on the pressure surface. In the high mass flux ratio condition, the effect of wake on the film cooling effectiveness is weakened on the suction surface and strengthened on the pressure surface.

Numerical investigation of blowing ratio, density ratio and axial position of film holes on the vane endwall film cooling effectiveness with upstream step

The aerothermal performance of interrupted slot and film holes was numerically investigated. Previous study indicates that the interrupted slot performs better compared to the conventional slot. In the meanwhile, the step formed along with the interrupted slot affects the film cooling characteristics. In this article, a row of film holes is arranged downstream of the step, and the mass flow rate for the interrupted slot is constant at 1%. Blowing ratio (BR) from 0.5 to 1.5 and density ratio from 1 to 2 were studied for the film holes. Endwall film cooling effectiveness distribution indicates that film cooling is easily affected by the secondary flow inside passage and the upstream step. Coolant traces are split into two parts due to the effects of step vortex and transverse flow. For different density ratios, increasing BR shows a different trend of film cooling effectiveness due to the variation of coolant momentum. The coolant jet is easily affected by the secondary flow when its momentum is low, but tends to liftoff when its momentum is too high. As a result, it is better to position the film holes far away from the upstream step. The total pressure loss coefficient distribution at the passage exit indicates that the coolant injection increases the total pressure loss. But density ratio has smaller effect on the loss variation. Besides, two axial positions of cooling holes were studied to improve the endwall cooling performance. Without the effect of step vortex, the film effectiveness of cooling holes is improved.

Elongated-Hexagonal Photonic Crystal for Buffering, Sensing, and Modulation

A paradigm for high buffering performance with an essential fulfillment for sensing and modulation was set forth. Through substituting the fundamental two rows of air holes in an elongated hexagonal photonic crystal (E-PhC) by one row of the triangular gaps, the EPCW is molded to form an irregular waveguide. By properly adjusting the triangle dimension solitary, we fulfilled the lowest favorable value of the physical-size of each stored bit by about Besides, the EPCW is highly sensitive to refractive index (RI) perturbation attributed to the medium through infiltrating the triangular gaps inside the EPCW by microfluid with high RI sensitivity of about 379.87 nm/RIU. Furthermore, dynamic modulation can be achieved by applying external voltage and high electro-optical (EO) sensitivity is obtained of about 748.407 nm/RIU. The higher sensitivity is attributable to strong optical confinement in the waveguide region and enhanced light-matter interaction in the region of the microfluid triangular gaps inside the EPCW and conventional gaps (air holes). The EPCW structure enhances the interaction between the light and the sensing medium.

Numerical Assessment of Density Ratio and Mainstream Turbulence Effects on Leading-Edge Film Cooling: Heat and Mass Transfer Methods

Abstract Within the context of leading-edge film cooling in a high-pressure turbine vane, the present study is a step forward toward modeling showerhead performance for a baseline geometry (namely four staggered rows of cylindrical holes) at engine-like conditions, starting from a previous investigation, at low-speed flow (exit isentropic Mach number of Ma2is = 0.2), low inlet turbulence intensity of Tu1 = 1.6%, and density ratio of DR ∼ 1. Those operating conditions, dictated by experimental constraints, were essential to validate results from delayed detached-eddy simulation (DDES) against off-the-wall measurements of velocity, vorticity, and turbulent fluctuations, for the coolant-to-mainstream blowing ratio of BR = 3 (momentum flux ratio of I = 9). Here, the potential of DDES is exploited to predict the aerothermal features of the flow in the leading-edge region in the presence of a larger density ratio (DR ∼ 1.5) and turbulent mainstream (Tu1 = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness (η), obtained by using the pressure-sensitive paint (PSP) technique. DDES predictions of η were computed using the species transport model (i.e., mass transfer), for comparison against the conventional thermal method, based on creating a temperature differential between the mainstream and the coolant (i.e., heat transfer). The simulated film cooling performance was found to depend on the method used, thus suggesting that other parameters than DR, BR, I, and Tu1 should be taken into account when the goal is matching engine-like conditions.