Inlet Slot Research Articles

Effects of modified intake surface to gasoline engine performance with the use of LPG

Indonesia observes a yearly rise in motor vehicle possession. Failure to consider alternate fuels in these trends may result in the depletion of gasoline. Out of the potential alternatives, Liquified Petroleum Gas (LPG) appears to be the most favorable. The sole issue lies in the elevated engine temperature and subsequent decrease in performance caused by its utilization. To address this vulnerability, it is advisable to employ a cooling injection method, such as water injection. Nevertheless, the rise in exhaust emissions linked to water injection highlights the necessity for optimization. This study aims to optimize coolant injection systems by conducting experiments with different modifications, such as conventional intake surfaces, dimple intake surfaces with gaps, and dimple intake surfaces without gaps. The gapless dimple inlet surface demonstrates superior performance in terms of exhaust emissions, power, and torque compared to both conventional inlet surfaces and slotted dimple inlet surfaces

Investigation of the relationship between combustion efficiency and total pressure gain for RDE

Total pressure gain is an important parameter in RDC engineering applications. Many factors affect the total pressure gain, such as the area ratio of the outlet to the inlet (A8/A3.1) and type of fuel. In this study, convergent–divergent slot and Tesla valve inlet configurations were adopted. Three convergent nozzles were used, and the ratios of the outlet area to the combustor cross-sectional area (A8/A3.2) were 0.65, 0.5, and 0.25, respectively. The experiments were conducted at mass flow rate of 1.5 kg/s, 1.3 kg/s, and 1.0 kg/s. The combustion efficiency and total pressure gain were calculated using the temperature increase and Mach-corrected static pressure (MCSP). When A8/A3.2 is 0.25, most of the propagation modes are longitudinal pulsed detonations (LPD). The combustion efficiency increased with the equivalence ratio within the range of the detonation boundary. A model was developed to describe the relationship between combustion efficiency and total pressure gain. Once the configuration of the RDC is fixed, a proportional relationship exists between the combustion efficiency and total pressure gain. Improving combustion efficiency enhances the total pressure gain.

Control of the boundary layer on compressor blade suction surfaces with the momentum jet

AbstractThe boundary layer thickness on a compressor blade suction surface increases rapidly under a adverse pressure gradient and even separates from the blade surface. This paper proposes a novel method for developing the slot inside the blade, with the inlet of the slot located at the leading edge of the blade and the outlet located at the suction surface, using the momentum of the incoming flow to form a high velocity jet to control the boundary layer on the suction surface. For a plane cascade with a diffusion factor of 0.45, the effects of the main slot parametres (such as the shape of the slot and the positions of the slot inlet and outlet) on the flow in the slot, the flow field and the aerodynamic performance of the cascade were investigated with a numerical method. When the aerodynamic performance of cascades with slotted and unslotted blades was compared, it was found that a reasonable slot structure can effectively inhibit the development of the boundary layer on the blade suction surface and greatly improve the aerodynamic performance of the cascade. Based on the influence of the slot parametres of the above cascade, the slot of a plane cascade with a diffusion factor of 0.60 was designed. The numerical calculation results show that the slotted cascade with a diffusion factor of 0.60 outperformed the slotted cascade with a diffusion factor of 0.45. This result showed that the higher the cascade load, the greater the performance improvement from slotting. Furthermore, the unslotted and slotted cascades were tested, and the test results agreed well with the calculations. The aerodynamic performance of the slotted cascade was better than that of the unslotted cascade, which verifies the accuracy of the calculation method and the feasibility of blade slotting for suppressing the development of boundary layers on suction surfaces and reducing flow loss.

AN OVERVIEW ON THE DESIGN VARIANTS FOR ORGANIZATION OF THE LIQUID FILM COOLING IN LPRE COMBUSTION CHAMBERS

Abstract. New technologies always create a trend to modernize and improve existing designs with new opportunities. At present, additive technologies have one of the most significant development rates among other manufacturing technologies. For modern liquid-propellant rocket engines, there is also a general trend towards increasing the efficiency of engines, finding new technological solutions that make it possible to simplify manufacturing technology, reduce technological costs and increase reliability. In this paper, known design solutions which employ film cooling for thermal protection of the walls of the engine chamber are considered. The main ways of organizing internal cooling are analyzed, the main mechanisms that define the thermal protection of the walls of the LRE chamber are considered. An overview of the existing design variants of devices which organize internal film cooling is given. The design solutions for film cooling of both the list of the real engines RD-105, RD-106, RD-0110, RD-115, RD-119 and known patent solutions are considered. The main features of such devices are shown and the influence of some design differences on the efficiency of the film cooling is analyzed. The main characteristics defining the efficiency of the device for film cooling are given. A review and analysis of the implemented design solutions for film cooling showed that the most efficient designs use the following elements, such as a gas-dynamic redan, a profiled wall of the predetermined space, and various types of inlet and outlet slots. Each design decision is based on the results of experimental testing of the engine. All these elements of film cooling design are very dependent on the accuracy of the manufacturing technology. Capabilities of additive manufacturing allow make it possible to create new designs with stable geometric characteristics in the form of a single part. The paper considers the options for applying the SLM additive manufacturing technology to create the design of the film cooling rings for liquid-propellant rocket engines.

Experimental investigation on reducing diesel particulate matter using centrifugal fluidised chamber

ABSTRACT Centrifugal fluidisation with static geometry, which is a new way of fluidisation, is still not getting the attention of engine researchers for reducing the PM from diesel exhaust. In the present work, centrifugal fluidisation with static geometry is used as an after-treatment method to reduce the PM from diesel exhaust. The centrifugal fluidised chamber with SiC particles was tested on air and diesel exhaust. Experimental results show that an increase in bed stability with an increase in inlets was responsible for improving chamber efficiency for 3 and 4 inlet chambers. The number of inlets, inlet slot width and the mass of a bed particle affect the fluidisation inside the chamber. For single-cylinder diesel engines, 3 and 4 inlet chambers show the potential to remove PM with maximum chamber efficiency close to 60%. The accumulation of bed particles is the main reason for the dropping of the chamber efficiency with time.

Corner separation control in compressor stators with jets from the blade leading edge

Corner separation occurs easily in highly loaded compressor stators. This paper proposes a novel slot inside the stator blade, with the slot inlet located at the blade leading edge and the slot outlet located at the suction surface, by using the momentum of the incoming flow to form a high velocity jet to control the development of the boundary layer on the blade suction surface. For 3D compressor cascades, the influence of the key geometrical slot parameters on the flow fields in the slot and cascade passage and the aerodynamic performance of the cascade were investigated with a numerical method. Then, the stator blades in a highly loaded compressor stage were slotted to improve the flow in the stator blade passages. The main results can be summarized as follows. The use of slotted blades in the cascade effectively suppresses corner separation. When the cascade inlet velocity is high or the inlet flow is at a positive attack angle, the separation control effect improves. In the highly loaded compressor stage, slotted stator blades considerably reduced the flow loss at the stator corner, and the stage efficiency increased over the entire flow rate range. Furthermore, two cascades with unslotted and slotted blades were tested. The experimental and numerical results were consistent, demonstrating that the total pressure loss coefficient of a cascade can be effectively reduced by slotting the blades in the cascade.

Effect of uniformly varying width leading-edge slots on the aerodynamic performance of wind turbine blade

According to the Betz limit, the maximum wind power that can be extracted from wind is limited to 59 %. Practically it stands at a 30–40 % level. Therefore, current research targets to increase the aerodynamic performance of wind turbines by introducing uniformly varying width (UVW) leading-edge slots. In present work, a UVW narrow channel is deployed using NACA (National Advisory Committee for Aeronautics) 4412 aerofoil, which starts from the leading-edge region and goes away to the pressure side of the aerofoil after a slight bending. NACA 4412 aerofoil is chosen as it has the highest lift to drag ratio. Six wind turbine blades of different dimensions (Gradually increasing Wi/Wo ratio) are proposed. Six proposed wind turbine blades are designed and analysed using CFD (computational fluid dynamics) with 0° to 16° at a 2° increment. Wind speed is taken at 7 m/s as per Indian conditions. Out of six proposed blade designs, NACA 4412 aerofoil (Wi/Wo = 2) gives 12 % spike lift to drag ration than the uniform slotted one. Again NACA 4412 aerofoil (Wi/Wo = 2) performs at its peak at angle of attack (AOA) 6°. It is observed that interaction of fluid separation zone and slot inlet results in a down grade of the aerodynamic performance of wind turbine blade. A scaled-down (one-fifth) model of the superior blade (made up of wood) and Solid blade have been made for the wind tunnel test and comparison. The computational results were compared from a series of wind tunnel tests.

Investigation of the temporal and spatial flow features within the high‐shear mixer by modal decomposition techniques

AbstractAn insightful comprehension of hydrodynamics in the high‐shear mixer (HSM) is crucial for its design and optimization. Therefore, the energetical and dynamical dominant features of inline HSM's velocity fields are extracted by proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), of which the sampling spaces are generated through Large‐Eddy Simulation. POD results reveal that the significant flow structures located in the shear gap and the adjacent regions of rotor/stator slot inlets comprise various energy levels. The strip‐shaped structures at the rotor/stator leading edges, wake and large‐scale vortices within the outflow region, and circulation inside the rotor slot are also visualized. DMD results emphasize the importance of flow patterns oscillating lower than rotor teeth passage frequency and reveal that the coherent structures shift and expand as their frequencies decrease. The POD and DMD analyses provide an insightful perspective of the spatial and temporal behaviors of the flow in HSM.

Investigation of the influence of jet supply configurations on the thermal and flow behaviors of the wall-attached night ventilation system

Facing the goal of carbon abatement to energy conservation and emission reduction, night ventilation has attracted increasing attention from scholars. As the night cooling performance is greatly influenced by the climate conditions, the wall-mounted attached night ventilation (WANV) has been proposed to achieve enhanced convective cooling performance for the region with a small diurnal temperature range. The present paper aims at investigating the airflow patterns and temperature field under different jet supply configurations. A numerical model is built and validated and further employed to evaluate the effect of supply air velocity, slot inlet location, and slot inlet angle. The dimensionless maximum velocity decay under different supply air velocities is established, while a slow jet velocity decay is found due to the buoyancy force driven by the heated wall. In addition, the thermal evaluation indicates that the supply air velocity of 4 m/s shows the best cooling performance. Considering the practical situation, the impact of the slot inlet orientation is further investigated. The results show that the critical dimensionless distance of the slot inlet to the adjacent wall s/b is 10 when the supply air velocity is 4 m/s, and the optimal installation angle for a large slot inlet distance is specified.

Effects of Divergence Inlet on Kerosene/Air Rotating Detonation Engines

In this paper, an improved three-dimensional conservation element and solution element method with chemical source terms is developed and applied to investigate the effects of different divergence inlet patterns on vapor kerosene/air rotating detonation engines. A two-step kerosene/air chemistry model is adopted and solved by a third-order Runge–Kutta method. A series of cases with varying the slot inlet width, in other words, 6, 4, and 2 mm, and divergence section length, in other words, 4, 6, and 10 mm, are simulated. The simulation results indicate the supersonic injection generated by the divergence section is helpful to decrease the disturbance from the downstream flow. Affected by the divergence section, the detonation front is divided into two sections, in other words, the main detonation front and the banded detonation front. For the main detonation front, the detonation strength on the outer wall is significantly stronger than that on the inner wall, while it is not for the banded detonation front. The total pressure loss caused by the inlet normal shock significantly increases with the decrease of slot inlet width. A declining deflagration surface will appear when a small slot inlet width of 2 mm is used. The rotating detonation engine (RDE) performance analysis shows that the slot inlet width has a significant impact on the thrust, specific impulse, total pressure gain, and outlet Mach number. A bigger slot inlet area ratio contributes to a higher total pressure gain. The simulation results can get insight into rotating detonation behaviors and guide the development of the kerosene/air RDE.

Numerical simulation of the nozzle configuration in strip casting process

This work examines the design of nozzles in continuous strip casting process. Three-dimensional (3D) simulations of steady turbulent (k-ε) flow are done at the upper part of the mould using a finite-volume (CFX) model. This is performed for different inlet systems, including the inlet nozzle jets with a free stream, the submerged nozzle jets, the slot inlet system, and the slot-submerged inlet system. The resulting heat flux to the solidifying shell has also been studied. Numerous operating parameters are examined, including the shape, size, position, and thickness of the ports and the bottom geometry. It is found that different inlet nozzle configurations change the molten flow and heat patterns, mainly in the upper region of the mould. By applying the slot nozzle inlet system, turbulence and values of the averaged velocity field in that area decrease significantly.

Benchmark study of 2D and 3D VOF simulations of a simplex nozzle using a hybrid RANS-LES approach

In this study, a simplex nozzle is tested with water for the benchmarking of different flow simulation models. A large scale Plexi-glass transparent nozzle is used to reduce the influence of production tolerances on the performance. Experiments are conducted at different flow rates and CD, spray angle and film thickness parameters are evaluated. 2D and 3D hybrid RANS-LES multiphase flow simulations of simplex nozzle are validated against the experimental data. Multiphase nature of the flow is modelled by volume of fluid method. The main goal is to assess the capabilities and drawbacks of 2D axisymmetric and full sector 3D modeling approaches. It is observed that although full sector 3D simulations require HPC cluster systems, accuracies in validation parameters are quite satisfying. Conversely, 2D axisymmetric simulations which can be run on a single core and give a general outlook of the flow field, they show an overshoot of CD and film thickness over the selected range of flow rate. It is shown that this overshoot is mostly related with the inlet boundary condition, which can not take the flow contraction and/or separation at the inlet slots into account. After correcting the inlet velocity 2D simulations by using the 3D results, it is shown that the predictions can be quite close to the experimental data.

Numerical simulations of vapor kerosene/air rotating detonation engines with different slot inlet configurations

To investigate the effects of slot inlet configurations on premixed vapor kerosene/air rotating detonation engines, a series of cases with different injection patterns, including baseline inlet, outer slot inlet, middle slot inlet, and inner slot inlet, are simulated by solving three-dimensional reactive Euler equations. Stable rotating detonation waves were obtained in the baseline and the outer slot inlet cases. Instead, an unsteady triple-wave mode was obtained in the middle slot inlet case and a decoupled detonation was observed in the inner slot inlet case. A long supersonic injection zone was observed in the outer slot inlet case and the main total pressure loss was found in the buffer zone. The propagation mechanism analysis demonstrates the crucial role of the outer wall in the propagation of rotating detonation waves, where the detonation waves near the outer wall tend to be over-driven and contributes to the stable propagation of detonations. A positive mass average total pressure gain of 48.0% was obtained in the baseline, confirming the total pressure gain ability of the kerosene/air rotating detonation engines. The simulation results indicate the area ratio between the outlet and the inlet is of great importance for obtaining the positive total pressure gain.

Comparing the performance of RANS turbulence models between different cavity flow benchmarks

To evaluate the performance of RANS turbulence models, this study compares four different cavity flow benchmarks using the prevailing two-equation turbulence models for indoor airflows, namely the standard and RNG k-ε and the standard and SST k-ω models. A cavity flow consists of one air inlet and one outlet slot. The inlet slot is positioned on the upper left corner of the cavity, whereas the outlet slot is located in the lower right. This cavity flow is representative of mixing ventilation. These four cavity benchmarks differ by their geometry (i.e., the aspect ratio of the room), flow regime and whether the flow is isothermal or not. Measurements of the air velocity and temperature in these benchmarks are used to evaluate the accuracy of the RANS turbulence models. Many existing studies have investigated the airflow and heat transfer over these benchmarks. However, the numerical methods and other relevant CFD parameters are not always described in detail, reducing the transparency and reproducibility of these works. To compare the influence of the RANS turbulence model on the four cavity flows, a same CFD setup is adopted here for all benchmarks. This setup is based on the best practice in RANS, namely a steady second-order spatial discretization on a wall-resolved structured mesh and with a grid convergence analysis. The results show that k-ε models, particularly the standard k-ε model, are best suited in a fully turbulent flow regime without strong pressure gradients. On the opposite, the SST k-ω model performs best in the transitional regime while the k-ε models only give moderate to poor results.

Experimental Study of the Diffusion of a Confined Wall Jet through a Perforated Plate: Influence of the Porosity and the Geometry

This paper investigated lateral diffusion of a confined two-dimensional wall jet (air inlet height: 5 cm) through a perforated plate. We considered two plates with porosities of and . The plates were positioned at distances of 10 cm and 20 cm below the jet inlet. The experiments were realized using 2D Laser Doppler Anemometer (LDA). Different profiles of mean and fluctuating velocities are presented. The presence of a perforated plate strongly modified the airflow pattern compared to an empty enclosure. The velocities above and below the plate depend on several parameters, including the porosity and the plate’s position relative to the inlet slot and the longitudinal position. The difference between the flow velocity above and below the plates could not be related using a universal formula that depends on these parameters. We also investigated the influence of a porous media of a height of 20 cm (a stack of spheres having a diameter of 3.75 cm) located below the perforated plate. The results highlight that the porous medium strengthens the effects of the perforated plate on the flow.

Swirling flow heat transfer and hydrodynamics in the model of blade cyclone cooling with inlet co-swirling flow

Swirling flow heat transfer and hydrodynamics were studied experimentally in the round passage, simulating the blade cyclone cooling. The smooth passage with one- and two inclined-tangential flow supply and the additional co-swirling flow at the inlet is considered. The Reynolds number, based on the average axial speed and passage internal diameter was ranged from 40 000 to 108 000, the co-swirling flow ratio Gd/GƩ was varied from 0 to 0.23. At Gd/GƩ ≤ 0.11 in the passage with one tangential slot the co-swirling flow influences weakly on the heat transfer enhancement and pressure drop ratio. In the passage with two slots, the Nud/Nud0 ratio drops down immediately from Gd = 0, moreover in this case the heat transfer is about 20% lower than that in the passage with one slot. At the identical total pressure in front of the passage, both schemes are comparable in terms of the total pressure losses. When pressure losses in swirl generators are taken into consideration at Gd = 0 two slots scheme demonstrates a greater Reynolds analogy factor than that for the one slot configuration. Also in terms of this factor, the two slots scheme looks better than the continuous and broken V-shaped ribs commonly used in the internal blade cooling. At Gd/GƩ > 0.5 - 0.6, the co-swirling flow reduces the heat transfer ratio and Reynolds analogy factor. In the passage with one inlet slot in the limited area of Gd/GƩ ratio, the pressure losses in the 90° exit bend are lower compared with the axial flow in the bend. In the passage with two slots in the entire range of Reynolds number, these losses are below those if the axial flow exists in the bend. This very attractive feature can be employed in the blade cyclone cooling design when the coolant discharges into the trailing edge area.

Velocity distribution of wall-attached jets in slotted-inlet ventilated rooms

The wall-attached jets for ventilation in spaces have been drawn considerable interest for their benefit of high ventilation efficiency and thermal sensation. In this study, the velocity distribution of a wall-attached jet under isothermal conditions in slotted-inlet ventilated spaces is investigated by experimental and numerical approaches. The wall-attached jet issues air from a slot inlet that flows down along the surface of a vertical wall, impinging on the floor attached to the vertical wall and spreading over the floor surface. The results show that the flow field of a wall-attached jet can be divided into three regions: vertical attachment region (region I), horizontal air reservoir region (region II), and jet impingement region. The correlation equations for the centerline velocity decay and velocity profiles are obtained. For the fully developed jet in region I and II, the dimensionless velocity profiles can be expressed as u0/um(y*)~(y*/b)γ and u0/um(x)~(x/b + Kh)γ, respectively, where γ is a constant related to the momentum decay rate. Over the whole range of jet flow conditions in this study, the value of γ is 1.11. Moreover, a unified exponential expression for the cross-sectional velocity profiles is proposed for both regions I and II. For the jet impingement region, the flow is complex and involves separation, reattachment, vortical flow, and pressure gradients. Large-scale vortices exist in the corner, and the vortices diminish as the jet inlet velocity increases. The current study can provide a theoretical basis for further engineering design applications of wall-attached jets for attachment ventilation.

Comparative studies on isothermal attachment ventilation based on vertical walls, square and circular columns

Ventilation and air distribution methods play an important role in indoor air quality and thermal environments. Effective airflow distribution within indoor environments has always been a great cause of concern. Attachment ventilation has drawn considerable interest since it is more energy efficient and space saving than traditional mixing or displacement ventilation methods. As a newly developed and applied attachment ventilation method, vertical wall-based attachment ventilation (WAV) was first proposed in the 1990’s by the authors. Later, the concepts of square column-based attachment ventilation (SAV) and circular column-based attachment ventilation (CAV) were also presented to meet the needs of more industrial applications. In this paper, three attachment ventilation methods— i.e., WAV, SAV and CAV are compared based on experimental studies and numerical simulations. For the vertical attachment region, semi-theoretical equations characterizing the dimensionless centerline velocity of WAV, SAV and CAV are proposed. The velocity profiles of all three types of attachment ventilation methods are similar. Of the three attachment ventilation methods, for the same distance y* along the attached wall measured from the slot inlet, the dimensionless centerline velocity of WAV is the largest, while those of SAV and CAV remain almost identical. In the horizontal air reservoir region (air lake zone), the semi-theoretical equations to predict dimensionless centerline velocity also are presented. The results show that for the same distance x normal to the wall/column, the dimensionless centerline velocity of WAV is the largest, followed by SAV and CAV. Additionally, unified semi-theoretical equations are presented for predicting the jet centerline velocity decay of attachment ventilation, which is helpful for the design of air distribution systems in heating, ventilation and air conditioning (HVAC) engineering applications.

Numerical prediction of the stratification performance in domestic hot water storage tanks

An efficient storage retains thermal stratification and improves the discharging performance. Turbulent mixing between hot and cold water is the prime source of stratification destruction. In this paper quantification of turbulent missing was achieved on the basis of temperature profile, MIX number, and Richardson number. The evaluated parameters include flow rate, ΔT, and diffuser design, henceforth a direct interdependence between each was thus established. Various CFD models were developed and experimentally validated on the test rig in order to find the optimal working conditions in discharge mode. The results proved numerically that the tank working conditions can be optimized by proper selection of inlet device. For instance, slotted type inlet device sustained maximum stratification even in as adverse a condition as of turbulent inflow & low ΔT. Perforated and simple inlet devices were capable of delivering best discharge efficiency only at low flow rate of 200 l/h and were showing insignificant dependency on ΔT. However, as flow rate is increased, ΔT dependency increased. Seeing the compounded benefits of slotted inlet devices and decreased ΔT, it was concluded that slotted inlet device delivered comparatively better thermal performance at both adverse conditions i.e. high flow & low ΔT and high flow & high ΔT, however, failed to outshine the rest of the inlet devices at low flow rate & low ΔT, and low flow rate & high ΔT. These research findings can serve as guidelines to optimize the storage tank design – more specifically, inlet device based design integrated with heating system, as thermal stratification and COP of heating system – heat pumps, for example, are inherently correlated. Heat pumps are high flow rate and low ΔT devices, while, solar systems are low flow rate and high ΔT devices, Thus, opting for accurate choice of inlet device for a particular operating condition is critical.

The interception capabilities of slotted drains as pavement surface drainage systems

The following two slotted drain installation scenarios were reviewed in this paper: a slotted drain operating individually without a median barrier and a slotted drain operating with an adjacent barrier installed along the longitudinal length of the drain. The interception capability of the two installation scenarios was experimentally reviewed and compared while imitating various conditions typically expected on South African pavements. The applied sheet flow, slotted inlet sizes and pavement slopes (longitudinal and cross slopes) were varied throughout the experiment. Interception efficiencies of the slotted inlets were experimentally calculated as a ratio of total intercepted sheet flow to the total sheet flow applied to the pavement layouts. The sheet flow applied during the experiment was analysed to estimate the rainfall intensities and flow depths that can typically occur on the different pavements for which the interception capability of the slotted inlets was reviewed. It was estimated that rainfall intensities of more than 1 000 mm/hr and flow depths higherthan 10 mm were imitated during the experiment. More than 98% of the maximum applied sheet flow of approximately 3.0 £/s/m was intercepted by the 30 mm slotted inlets regardless of the pavement slope values and type of slotted drain layout. The conclusion reached was that both these slotted drain installation scenarios operating in practice for the conditions tested would have the capability to sufficiently remove the surface water to promote road safety during wet pavement conditions.