Open Area Ratio Research Articles

Application of a novel stall margin improvement indicator in optimizing casing treatment for a transonic compressor

This paper presents a multi-objective design optimization of axial slot casing treatments in a 1.5 stage transonic compressor. To perform the optimization, an in-house optimization design platform is constructed using genetic algorithm and Kriging surrogate model. The optimization objectives are the peak efficiency at the design rotating speed and the stall margin improvements at both design and off-design rotating speeds. Instead of massive unsteady simulations that are required to accurately predict the stall margin, a stall margin improvement indicator is introduced based on the time-averaged axial momentum budget analysis at the rotor tip region. With this indicator, only one steady simulation is needed to evaluate the stall margin enhancement ability of a new casing treatment design at a given rotating speed. The axial slots are parameterized with a total of eight design parameters. The meridional profiles are described with two B-spline curves to define parameters such as the size, axial position, and shape of the slots. Circumferential parameters include the open area ratio and inclination angle. When the optimization finally converges, different optimal variants are selected from the database and their effects are investigated with both experiments and numerical simulations. The detailed flow fields are analyzed in depth with results from unsteady simulations. The application of the optimal casing treatments exerts a suction and re-injection effect, pushes the interface between tip leakage flow and incoming main flow downstream and reduced flow blockage in the blade tip region. Consequently, the stability of the compressor is significantly improved.

Effect of open-area ratios on wave attenuation over a submerged reef breakwater: An experimental study

The reef-type submerged breakwater (RSB) has been implemented around the world to provide coastal protection and natural shelter and habitat for marine species at the same time. A series of laboratory experiments are conducted in a wave flume to study wave propagation and transmission over RSBs with the four open-area ratios of 0.047, 0.131, 0.257, and 0.560. The experimental results demonstrate that the RSB significantly alters the wave propagation characteristics. The RSBs with the open-area ratio of 0.047 and 0.131 reduce the wave height to ∼70%. The RSBs with the open-area ratio of 0.047 and 0.131 perform better in attenuating than those with the open-area ratio of 0.257, and 0.560. As the open-area ratio decreases, the transmission coefficient decreases, while the dissipation coefficient increases. An empirical formula is proposed to calculate the wave transmission coefficient as a function of the RSB open-area ratio and wave steepness under regular waves. A cubic empirical formula with one unknown is also proposed to relate the distance from RSB stoss face to wave breaking point and the open-area ratio. The present study is expected to optimize RSB design for coastal protection.

Experimental study on the propagation mechanism of acetylene-air detonation waves in a unilaterally intermittently constrained channel

This study experimentally explores the propagation mechanisms of acetylene/air detonation waves within a channel intermittently constrained on one side, utilizing soot foil and high-speed schlieren photography to capture the cellular structure and shock-flame evolution. The experiments revealed that the detonation waves traverse the semi-enclosed channel with various discrete wall configurations on the side in three distinct propagation modes: (I) periodic detonation failure and re-initiation; (II) single extinction and re-initiation; (III) non-extinction. Mode I occurs exclusively when the open area ratio exceeds 0.85, while detonation tends to favour Mode II when the gaps between discrete walls exceed three times the cell size; otherwise, it tends towards Modes III. The re-initiation mechanism of detonation involves curvature shocks inducing local explosions of reactive mixtures through multiple Mach reflections off the discrete walls. The self-sustained propagation mechanism of the detonation wave is maintained by the interaction of strong transverse shocks reflected from discrete walls with the inherent transverse waves within the detonation structure, sustaining the instability of the cellular detonation.

Performance analysis and optimization of solar air heater with double-pass configuration using perforated blocks and semi-circular tubes as artificial roughness

The low heat transfer and thermal efficiency of the solar air heater are primarily caused by the formation of a thermal boundary layer along the absorber plate, which contributes to the low convective heat transfer coefficient between the absorber and air. The use of different artificial roughness geometries enhanced the turbulence that help to supress region of hot spot on the absorber plate more effectively and reduce the thermal boundary layer on the absorber for improved heat transfer. In light of this, the present study explores the double-pass configuration of solar air heater equipped with perforated blocks and semi-circular tubes together as artificial roughness on the performance metrics. The mathematical modeling is performed to evaluate the effect of design parameters: tube amplitude ratio (at/Hd), open area ratio (β) and blockage height ratio (eb/Hd), on thermal and effective efficiency at different Reynolds numbers (Re) and solar irradiation (I). Among the parameters studied, the maximum thermal efficiency is found to be 85.36 %, at eb/Hd of 0.8, at/Hd of 0.3, β of 30 %, Re of 19,000 and I of 1000 W/m2. The maximum effective efficiency has been evaluated, which is found to be 81.89 %, at at/Hd of 0.3, eb/Hd of 0.4, β of 30 %, Re of 11,000 and I of 1000 W/m2. In addition, novel correlations have been established for thermal and effective efficiency, showing absolute percentage errors of 0.2 % and 2.2 % respectively. The results indicate enhanced performance in terms of both thermal and effective efficiency, outperforming earlier designs.

Integrated Thermal Management System Concept With Combined Jet Plate, High Porosity Aluminum Foam, and Target Plate for Enhanced Heat Transfer

Abstract An experimental investigation was carried out on high porosity metal foams subjected to array jet impingement with an objective to develop enhanced heat transfer configurations. In this study, we propose an integrated thermal management system (TMS) aimed toward leveraging the conjugate heat transfer capabilities of target plate, metal foam, and the jet plate—all made from aluminum and assembled such that a proper contact between them can be established. Steady-state heat transfer experiments were carried out for 10 and 20 pores per inch (PPI) aluminum foams of 0.93 porosity. Both metal foams were 12.7-mm thick. The normalized jet-to-jet spacing was varied from 2 to 12 times the jet diameter, while the jet diameter was fixed. The ratio of the jet plate thickness and jet diameter (nozzle aspect ratio) was 6.35, which ensured proper development of jets inside the nozzles. Experiments were conducted over a wide range of Reynolds number (based on jet diameter) varied from 100 to 5000. The obtained convective heat transfer coefficient for different configuration was evaluated in context with pressure drop. The analysis of experimental results reveal that large open area ratio jets combined with high porosity metal foams provide highly efficient and high-performance cooling for the investigated range of Reynolds numbers.

Central cone film cooling scheme of turbofan engine based on multi-fidelity simulation

To improve the computational efficiency of multi-fidelity simulation, an improved fully coupled method was proposed, which was applied to the coupled simulation of a 3-D model of an exhaust system and a 0-D model of a turbofan engine. Different from conventional approach, by “truncating” the engine model, the CFD calculation of the exhaust system can be decoupled from the solution of nonlinear equations in the engine model, and an outer iteration equation set was constructed to solve the multi-fidelity model. It was found that the improved fully coupled method has better computational efficiency than traditional methods while maintaining equivalent computational results. Then, the improved fully coupled method was applied to the design of the central cone film cooling system, the influence of cooling gas bleed mechanism, the hole open area ratio of the central cone and hole density, hole direction, hole shape on the infrared characteristics was investigated. The impact of central cone film cooling on the overall performance of the engine was quantitatively evaluated. Combined with various favorable factors, when maintaining the HP rotor speed unchanged, the integrated infrared radiation intensity of the central cone under supersonic cruise conditions is reduced by 93 % compared to the uncooled state, while the engine thrust increases by 0.3 % and fuel consumption rate increases by 0.18 %. The multi-fidelity simulation method proposed in this paper and the conclusions obtained are of great significance for the structural design of low-infrared exhaust systems.

Numerical Study on Effect of Flow Field Configuration on Air-Breathing Proton Exchange Membrane Fuel Stacks

Air-breathing proton exchange membrane fuel cells (PEMFCs) show enormous potential in small and portable applications because of their brief construction time without the need for gas supply, humidification and cooling devices. In the current work, a 3D multiphase model of single air-breathing PEMFCs is developed by considering the contact resistance between the gas diffusion layer and bipolar plate and the anisotropic thermal conduction and electric conductive in the through-plane and in-plane directions. The 3D model presents good grid independence and agreement with the experimental polarization curve. The single PEMFC with the best open area ratio of 55% achieves the maximum peak power density of 179.3 mW cm−2. For the fuel cell stack with 10 single fuel cells, the application of the anode window flow field is beneficial to improve the stack peak power density compared to the anode serpentine flow field. The developed model is capable of providing assistance in designing high-performance air-breathing PEMFC stacks.

An Investigation of the Acoustic Enclosure of an Air Conditioning Compressor Using Response Surface Analysis and Topological Rigidity Optimization

A novel split-type air conditioning system is introduced to balance usability and portability. Unlike conventional split-type systems, where the compressor is typically placed outside, this system situates the compressor within the indoor unit, which may expose users to compressor noise. There are prominent peaks in the compressor noise spectrum, particularly at the compressor operating frequency and its harmonics, notably the second and third harmonics. The research presents a multilayered acoustic enclosure specifically designed for air conditioning compressors to address this issue without modifying the compressor or indoor unit casing. In order to get better sound insulation performance, a response surface methodology (RSM) is applied to optimize the thickness ratio, open area ratio, and open area height of the acoustic enclosure with predefined thickness. In addition, topological optimization is employed to strengthen weak areas of the acoustic enclosure. Then, experimental trials using the proposed acoustic enclosure are conducted in a semianechoic chamber. Results demonstrate significant reductions in noise levels, including 7.99 dB(A), 5.69 dB(A), and 5.19 dB(A) reductions in the fundamental frequency, second harmonic, and third harmonic noise of the compressor’s operating frequency, respectively.

Single-shot fast cinematic imaging during merging process of multiple electron filaments in electrostatic potential well.

For the first time, details of the spatial and temporal acceptable evolution of the merging process of co-rotating electron vortices in a potential well are successfully captured using a "single-shot method" with a high temporal resolution of 10 µs. Four-electron filaments are trapped inside the Beam eXperiment-Upgrade linear trap [H. Himura, Nucl. Instrum. Methods Phys. Res. A 811, 100 (2016)] with a uniform axial magnetic field and co-axial multi-ring electrodes. Images of non-emitting electron filaments are captured using a high-speed camera with up to 1 000 000fps, a microchannel plate, a fast-decay phosphor screen of which fluorescence duration is 0.15 µs, and a super fine metallic mesh with an open area ratio of 89%. Images captured every 10 µs clearly show the growth of multiple short-wave instabilities in the wing trailing electron vortices. The experimental methods and measurement techniques presented in this paper can contribute to revealing exactly how small vortices evolve into a large structure or turbulence in a potential well through complex processes.

Critical analysis of the energy and exergy performance of an air heater duct with perforated 60-degree V-down baffles affixed to the heated surface

The indirect-mode solar dryer, with a solar air heater as a vital component, is commonly preferred for enhancing agricultural product quality. Energy and exergy analyses for an air heating system assess thermal gain and irreversibility in energy conversion. According to the literature, the easiest way to enhance the SAH’s energy and exergy performance is by incorporating flow-modifying elements or turbulators in the air passage. And the effective-energy assessment accounts for the increased airflow pumping power demands. This work aims to experimentally compare the energy and exergy performance of a smooth air heater duct with one integrated with perforated V-shaped baffles while critically examining the factors leading to the efficiency variations. The racetrack-shaped perforated V-baffles with 60-degree air attack angles are installed on the heated surface with V-down and staggered hole arrays, covering a turbulent flow Reynolds number (Re) range of 5400–13,100 during experimentation. The investigation involves varying the pitch-to-duct depth ratio (p/H) of baffles (with values of 1, 2 and 3) and considering two different hole-aspect ratio (w/d) values of 5.04 and 2.68, with the same open area ratio. The results reveal that baffles with w/d of 2.68 at p/H of 3, causing enhanced airflow turbulence and momentum diffusivity, provide the highest effective-energy ([Formula: see text]) and exergy ([Formula: see text]) efficiencies values of 88.7% and 12.44%, respectively, at Re of 11,816 and 8765. Based on the operating and geometrical parameters used in the experiments, the correlations of [Formula: see text] and [Formula: see text] developed demonstrate good accuracy. The values for mean absolute error, root mean squared error and R 2 (coefficient of determination) in the correlations, developed using the statistical computing R software, are 0.012427, 0.014837 and 0.9913 for [Formula: see text] and 0.004332, 0.005047 and 0.9557 for [Formula: see text], respectively.

The Effect of Inlet-Outlet Position and Ratio on Airflow Patterns and Privacy in Low-Cost Flat Units in Surabaya

A low-cost rental flat is a vertical building with natural ventilation as the primary ventilation source for its units. In practice, residents do not use room openings optimally because it tends to reduce room privacy. The consideration of the position and inlet-outlet area ratio is essential to create better privacy with airflow patterns that support room activities. The research consists of two stages. The first stage was carried out using qualitative methods, which proved the utilization of openings in the hallway side influenced user privacy. This paper discusses the results of the second stage, which was carried out using quantitative methods. The research aims to solve low-cost flats’ cross-ventilation problem. Data collection using quantitative methods based on observations, data analysis using simulations of airflow patterns, and distribution analysis tables. The results show that the airflow pattern in the existing design does not support the resident’s activities with the applied room openings having poor privacy. The proposed designs with privacy parameters consideration, an opening area ratio of 1 (inlet): 1.6 (outlet) and a ratio of 1 (inlet): 2 (outlet) shows an average increase of 50% in airflow velocity and privacy in the unit room compared to the existing design.

Simplified vented acoustic window with broadband sound transmission loss

A vented window design is presented allowing for air ventilation and improved sound reduction for urban traffic noise. The window design aims to be of simple construction, consisting of double-glass cells with a two-sided vent opening and a single internal division that splits the inner cavity into two resonators tuned at about 200 and 400 Hz. The basic window cell is modeled by means of a transmission matrix model, as well as through a finite element simulation. These provide an insight into the physical performance principles of the device, and produce results comparable with the acoustic measurements. Preliminary experiments showed the convenience of covering the resonator openings with flow-resistive absorbing material. This helps in raising the spectral sound transmission dips, improving the single number rating according to ISO 717-1:2020 with a measured weighted sound reduction index Rw(C,Ctr)=18(0;0) dB. The comparative performance of the window related to other windows reported in the literature is shown in a graph relating sound reduction and open ventilation area ratio. A reference performance curve is proposed corresponding to the maximum sound transmission loss of a pure constriction with the same open area. The sound reductions offered by different windows can be compared depending on how much their performance, according to Rw, departs above or below this reference curve. The window design performs according to the reference curve.

Experimental and numerical investigations on bending behavior of fixed open-web steel beams

The effects of opening parameters on the bending behavior of fixed open-web steel beams under static loading were experimentally investigated using six specimens of different opening length-to-height ratios, area ratios, and distributions. The experimentally obtained failure modes, bearing capacities, and load-displacement curves of the specimens were compared with those extracted from numerical simulations performed via Abaqus finite element analysis software. The results revealed the following: (i) The typical failure mode of the fixed open-web steel beams was plastic failure at the opening corners in the shear-bending sections, with compressive corners experiencing flexion and tensile corners experiencing tearing. (ii) For a given opening area ratio and opening height-to-beam height ratios, decreasing the opening length and increasing the number of openings significantly increased the bearing capacity of the open-web beam (by more than one-fold) when the openings were appropriately configured, compared with beams with a small number of large openings. (iii) Increasing the opening height and length had similar effects on the bending behavior of the open-web beam.

A comparative study of internal heat transfer enhancement of impingement/effusion cooling roughened by solid rib and slit rib

In the present study, we conducted a conjugate heat transfer (CHT) analysis for double-wall cooling with impingement and effusion, incorporating various types of ribs, using the Reynolds-averaged Navier–Stokes (RANS) method and the modified shear stress transport (SST) turbulence closure model (SST-KIC), accounting for the Kato-Launder modification (K), intermittency (I), and crossflow (C) transition effects. We comprehensively discussed the impact of slit type (parallel, inclined, convergent, and divergent), open-area ratio (β = 5%, 20%, and 40%), and jet Reynolds number on the turbulent flow and heat transfer in a double-wall cooling with slit ribs. Our findings indicated that the introduction of slit ribs significantly improved heat transfer and its uniformity on the target wall, albeit with a slight increase in pressure loss. The overall Nusselt number and thermal-hydraulic performance (THP) in cases with slit ribs gradually decreased with β, yet remained up to 17% and 13% higher than those observed on a smooth target wall. Notably, the open-area ratio of the slit rib exhibited a more pronounced effect on heat transfer over the target plate. For the divergent slit rib within the Reynolds number range of 4000–16 000, the heat transfer enhancement ratio reached the highest value at β of 0.05. In addition, we computed the entropy production caused by fluid friction and heat transfer, as well as the overall entropy production in double-wall cooling at different β and Re. The analysis revealed that the slit rib target plate performed better than the solid rib target plate, showing a distinct advantage in terms of total entropy production.

Influence of Open Area Ratio in Distributor on Wall to Bed Heat Transfer Coefficient from a Single Horizontal Tube to Fluidized Bed of Large Particles

Influence of Open Area Ratio in Distributor on Wall to Bed Heat Transfer Coefficient from a Single Horizontal Tube to Fluidized Bed of Large Particles

Numerical study on the effect of optimizing the Trombe wall structure with built-in fins on improving building energy efficiency in severe cold region

In order to save heating energy and reduce carbon emission intensity, a floor heating room with built-in finned Trombe wall in Xining, Qinghai, a severe cold area, was taken as the research object. And ANSYS 2021 R1 was used to numerically investigate the effects of several major factors, such as fin height, fin transverse distance, fin longitudinal distance, fin inclined angle, fin shape, perforated shape and perforation ratio of perforated fin, on the average heat transfer coefficient (h) between the absorptive surface and the air in the interlayer. The results show that for fins with low heights, the enhancement effect of horizontal fins on the convective heat transfer of the absorptive surface of Trombe wall is greater than that of vertical fins. The enhancement effect of vertical fins on the convective heat transfer of the absorptive surface is more affected by fin transverse distance, while the enhancement effect of horizontal fins on the convective heat transfer of the absorptive surface is more affected by fin longitudinal distance. Besides, h shows a trend of first increasing and then decreasing with the increase of fin inclined angle, and reaches its maximum value of 5.89 W/(m2·K) at 45°. The fins with different shapes are equilateral triangular fins, semicircular fins, isosceles triangular fins and rectangular fins in descending order of their enhancement effect on the heat transfer of wall. Compared with solid fins, fins with circular holes can obtain a better convective heat transfer effect only when the open area ratio is 1:6. While fins with equilateral triangular holes can obtain better convective heat transfer effect as long as the open area ratio is greater than 1:7. Fins with elliptical holes do not significantly improve the heat transfer effect. On the basis of optimizing the fin layout and structure, the thermal performance of the improved Trombe wall during the 8:00∼16:00 period and its impact on indoor thermal comfort of the building were studied, and the energy-saving performance of the plan was discussed. Compared with the Trombe wall room with no fins, the improved Trombe wall can improve the heat teransfer efficiency and the building energy saving rate by 68.50 % and 53.57 %, respectively. The improved Trombe wall can only ensure the indoor thermal comfort in limited several hours, in the rest of time, the residents should add clothing to keep warm. These conclusions have an important effect of engineering guidance and great realistic meanings for promoting the process of solar building integration and achieving the “carbon peak and carbon neutrality” target.

Evaluation of space comfort based on occupant satisfaction in west Jatinegara flats residential units

The Special Capital Region (DKI) of Jakarta is an area that experiences population growth every year, which raises the number of housing-related needs and reduces the amount of available vacant land for housing. In order to get around the lack of land for housing, a plan for flats—like the West Jatinegara Flats—must be implemented. The spaces in an apartment that are designed by an architect are required to produce a design that takes into account the comfort factor of the space for the occupants or users in addition to aesthetics. Residents feel comfortable if they are at a thermal temperature of between 22.8℃-25.8℃ with humidity of 70%. The study, "Evaluation of Space Comfort based on Occupant Satisfaction in West Jatinegara Flats Residential Units," attempts to ascertain whether or not improving strategies are required to raise space comfort based on occupant satisfaction and whether or not an appropriate level of space comfort is achieved. This study employs the quantitative method, which entails gathering primary and secondary data and conducting interviews with at least 10% of the resident population selected at random. This study's results indicate that improvement strategies are required to improve room comfort. These strategies include organizing each room to make it cozier and more compact, considering the type of opening material, the opening area ratio, and the materials used for the glass and frame to prevent breakage and damage to the windows and handles. Every room in the residential unit needs to have optimal air exchange during strong wind conditions.

Further Investigation of Impedance Eduction in a Grazing Flow Duct Facility

An established protocol for impedance eduction is based on a search procedure in which wall impedance in a duct propagation model is varied to obtain an acoustic field converging with one measured in a grazing flow duct. Here, an acoustic velocity potential formulation for the finite element model propagation model is extended to examine the relative effectiveness of driving the model with measured acoustic pressure at the source and termination and driving with acoustic pressure at the source and closing the computational domain with measured termination impedance. Also assessed is the appropriate location of measurement microphones to satisfy plane wave requirements for the computational model. Source acoustic pressure and termination impedance driving the propagation model produce superior eduction results with lower residual error, though the model driven with pressure at both the source and termination produces acceptable spectra. The microphone location in the gazing flow test facility is judged to be adequate for the range of grazing flow Mach number and frequency considered. Examination of impedance spectra for a range of lining samples has revealed a correlation of a decrease in spectrum quality, measured by observed data scatter, with a decreasing face sheet open area ratio and therefore with increasing lining nonlinearity.

Understanding the effect of design parameters on the filtration efficiency of trawls intended for commercial harvesting of zooplankton

A major challenge for the aquaculture sector is access to sustainable and cost-effective raw materials for feed. Copepods (Calanus spp.) have potential to meet this need for large volumes of marine raw materials to enable sustainable growth of aquaculture production worldwide. However, the lack of an energy- and catch-efficient trawl technology has limited the development of this fishery in the Northeast Atlantic. Therefore, the goal of this study was to develop a next generation trawl for harvesting zooplankton that was less energy demanding and more catch efficient than current trawl designs. We assessed the filtration efficiency of low porosity nets with different solidities and studied the effects of design parameters (mesh opening, twine thickness, porosity, taper angle) at various flow velocities in a flume tank. We found that the filtration efficiency for a square meshed net increased with increasing velocity and decreasing solidity and taper angle. A large open area ratio (the ratio between the open netting area and the net's mouth area) improved the filtration efficiency at towing velocities below 0.5 ms−1. These results provided an indication of the initial filtration efficiency of the net designs (i.e., before any clogging occurs) but not of the sustained filtration efficiency.

Dynamic rule-based change-over ventilation strategy with weather-responsive air-conditioning setpoints

Recent studies have actively developed dynamic rule-based mixed-mode ventilation (MMV) strategies to manage indoor thermal quality in an energy-efficient manner. Existing research on the dynamic rule-based MMV control has mainly focused on window opening area ratio calculation with fixed setpoints of mechanical operation. However, using fixed setpoints tends to force mechanical operation, though the outdoor temperature is suitable for natural ventilation. For this reason, this study questions whether a rule-based MMV strategy can effectively manage indoor thermal quality and reduce air-conditioning (heating and cooling) load when incorporated with the methods adjusting operation variables of both active and passive systems. To address this research question, this study proposes a dynamic rule-based change-over ventilation strategy integrated with three control components. First, a rule-based control component for adjusting air-conditioning setpoints is developed. Second, an operation mode selection scheme is proposed to decide the appropriate mode for fulfilling thermal demands. Third, a dynamic window opening area ratio function is proposed to provide a sufficient cooling effect to rooms when natural ventilation is required. The proposed strategy integrated with these key components is optimized for each space by non-dominated sorting genetic algorithm II. As a result of the optimization, the proposed strategy reduces 59.77% of the total cooling and heating load against the baseline, which fully operates the building by mechanical systems while ensuring 97.75% of thermally comfortable periods relative to the entire occupied period. Conclusively, this study identified that dynamically adjusting operation thresholds in MMV strategy achieves a substantial load reduction rate and ensures thermal comfort.