Flat Plate Configuration Research Articles

Biomimetic Wings for Micro Air Vehicles.

In this work, micro air vehicles (MAVs) equipped with bio-inspired wings are investigated experimentally in wind tunnel. The starting point is that insects such as dragonflies, butterflies and locusts have wings with rigid tubular elements (corrugation) connected by flexible parts (profiling). So far, it is important to understand the specific aerodynamic effects of corrugation and profiling as applied to conventional wings for the optimization of low-Reynolds-number aerodynamics. The present study, in comparison to previous investigations on the topic, considers whole MAVs rather than isolated wings. A planform with a low aperture-to-chord ratio is employed in order to investigate the interaction between large tip vortices and the flow over the wing surface at large angles of incidence. Comparisons are made by measuring global aerodynamic loads using force balance, specifically drag and lift, and detailed local velocity fields over wing surfaces, by means of particle image velocimetry (PIV). This type of combined global-local investigation allows describing and relating overall MAV performance to detailed high-resolution flow fields. The results indicate that the combination of wing corrugation and profiling gives effective enhancements in performance, around 50%, in comparison to the classical flat-plate configuration. These results are particularly relevant in the framework of low-aspect-ratio MAVs, undergoing beneficial interactions between tip vortices and large-scale separation.

Temperature-Driven Instabilities in High-Pressure Vessel Flat Plates: A Thermal Buckling Study

In the realm of high-pressure vessel simulation, conventional finite element method (FEM) approaches, as per ASME standards, may inadequately predict the behavior of flat surfaces under elevated temperatures. This study challenges the efficacy of shell-type mesh modeling for high-temperature flat plates, demonstrating that the thermal conditions within such high-pressure vessels can induce thermal instability and buckling, not accounted for by traditional FEM methods recommended by ASME. Through comprehensive analytical investigations, we reveal that traditional shell-type meshing techniques, while suitable for certain applications, fail to capture the intricate thermal stresses and deformation patterns inherent in high-temperature flat plate configurations. Our analysis delineates distinct stability regimes governed by key design parameters, including plate thickness, operating temperature, and geometric dimensions, profoundly impacting the structural integrity of heating plates under thermal loading. Specifically, we found that increasing the plate thickness enhances resistance to thermal buckling, clamping the plate edges raises the critical buckling temperature, and selecting materials with lower thermal expansion coefficients improves stability. These findings provide engineers with critical insights necessary for optimizing the design and performance of high-temperature equipment. This includes the design of high-pressure vessels with flat surfaces for heating materials, flanges in high-temperature environments, and fins in heat exchangers across various industries such as oil and gas, pyrolysis, and power plants. The findings presented herein serve as a valuable reference for engineers seeking to comprehend and mitigate instability phenomena in solid mechanics, offering practical guidance for developing robust and reliable high-temperature structures in demanding industrial environments.

Large eddy simulation of shock wave/boundary layer interactions in a transonic compressor cascade

In this paper, large eddy simulation (LES) was performed to investigate the shock wave/boundary layer interaction (SBLI) phenomenon in transonic compressor cascades with a chord Reynolds number of 2.12 × 106. A comprehensive analysis was conducted on both the SBLI structures inherent to the transonic compressor cascade and the coherent vortex structures within the boundary layer. The underlying mechanisms of the shock-induced boundary layer transition and the shock low-frequency unsteadiness in the transonic compressor cascade were elucidated through spectral and dynamic mode decomposition (DMD) analysis. The results revealed that boundary layer separation induced by the SBLI cannot reattach, leading to the formation of large-scale coherent vortex structures. Spectral analysis revealed that the shock-induced boundary layer transition in the transonic compressor cascade was dominated by inviscid Kelvin–Helmholtz (K–H) and secondary instability mechanisms, characterized by a dimensionless Strouhal number of 0.06. Additionally, pressure signals showed the variations in sub-frequency from the separated shear layer to the main flow. The oscillation amplitude of the shock foot was significantly greater than that of the shock main body, and the oscillation frequency of the shock foot was consistent with the sub-frequency. The oscillation frequency of the shock main body coincided with that of the compression ramp and flat plate configurations. Finally, DMD modal analysis indicated that high-frequency modes were correlated with turbulent fluctuations in the boundary layer, while medium- and low-frequency modes corresponded to shedding motion in the separated shear layer and low-frequency motion of the shock. This work promotes the understanding of the complex flow mechanisms of SBLI in the transonic compressor cascades.

Flow and heat transfer on the pressure side of C3X vane with various cooling hole blockages

Performance of film cooling under blockage has been extensively studied on flat plates. However, the ideal film cooling patterns obtained from flat plates may not be directly applicable to realistic engineering applications involving curved vanes or surfaces. The pressure gradient on a curved surface can significantly alter the behavior and trajectory of the coolant jet. This can result in variations in film cooling effectiveness and heat transfer characteristics compared to flat plate configurations. Therefore, in this study, a conjugate heat transfer numerical simulation was performed on the C3X vane under three sorts of cooling hole blockages including all-round blockage (RB), leading-edge blockage (LB), and trailing edge blockage (TB) with blockage ratio of 0.2, 0.35 and 0.5, respectively. Results show that RB changes the cooling effectiveness in the mid-span section nonlinearly, the cooling effectiveness was decreased by (0.019, 0.023, 0.038). LB is found beneficial to local film cooling downstream the cooling hole near the mid-span and tip area of a vane at blockage ratio of 0.2 with an increment of 0.021 in the mid-span section and 0.013 in 86% span section. As the blockage ratio increases to 0.35 and 0.5, LB produces adverse influences and the mid-span cooling effectiveness was decreased by 0.013 and 0.043, respectively. TB riseed the cooling hole outlet temperature marginally. The cooling effectiveness near the hole outlet in the mid-span section was decreased by (0.020, 0.034, 0.024). However, under blockage ratio of 0.2 and 0.35, the coolant jet is found to reattach the vane surface, resulting in improved film cooling effectiveness.

Transducer Resolution Effect on Pressure Fluctuations Beneath Hypersonic Turbulent Boundary Layers

The size of a pressure transducer is known to affect the accuracy of measurements of wall-pressure fluctuations beneath a turbulent boundary layer because of spatial averaging over the sensing area of the transducer. In this paper, the effect of finite transducer size is investigated by applying spatial averaging or wavenumber filters to a database of hypersonic wall pressure generated from a direct numerical simulation (DNS) that simulates the turbulent portion of the boundary layer over a sharp 7° half-angle cone at nominally Mach 8. A good comparison between the DNS and the experiment in the Sandia Hypersonic Wind Tunnel at Mach 8 is achieved after spatial averaging is applied to the DNS data over an area similar to the sensing area of the transducer. The study shows that a finite sensor size similar to that of the PCB132 transducer can cause significant attenuation in the root-mean-square and power spectral density (PSD) of wall-pressure fluctuations, and the attenuation effect is identical between cone and flat plate configurations at the same friction Reynolds number. The Corcos theory is found to successfully compensate for the attenuated high-frequency components of the wall-pressure PSD.

Influence of deep gaps on laminar–turbulent transition in two-dimensional boundary layers at subsonic Mach numbers

Systematic experimental investigations on the influence of deep gaps on the location of laminar–turbulent transition are reported. The tests were conducted in the Cryogenic Ludwieg–Tube Göttingen, a blow-down wind tunnel with good flow quality, at eight different unit Reynolds numbers ranging from Re_1 = {17.5,,times 10^{6},mathrm{{m}^{-1}}} to 80,times,10^{6},mathrm{m}^{-1}, three Mach numbers, M= 0.35, 0.50 and 0.65, and various pressure gradients. A flat-plate configuration, the extended two-dimensional wind tunnel model PaLASTra was modified in order to allow the installation of gaps with nominal widths of 30 upmu m, 100 upmu m and 200 upmu m and a depth of d = {9,mathrm{mm}}. A maximum Reynolds number based on the gap width Re_{w} = Re_1 cdot w approx {16{,}000} was reached. Transition Reynolds numbers ranging from Re_{tr}approx 1 × 106 to 11 × 106 were measured, as a function of gap width, pressure gradient and Mach and Reynolds number. This systematic investigation facilitates a linear approximation of Re_{tr} dependent on the boundary layer shape factor H_{12} for various flow conditions and gap widths. It was therefore possible to conduct an investigation of Re_{tr} depending on Re_{1} and the relative change of the transition location depending on the gap width w. Incompressible linear stability analysis was used to calculate amplification rates of Tollmien–Schlichting waves and determine critical N-factors by correlation with measured transition locations. The change in the critical N-factor varDelta N by installation of the gap is investigated as a function of w and Re_w. It was found that a gap width of 30 upmu m reduces the critical N-factors in the range of varDelta N approx 0.5 pm 0.25, while gap widths of 100 upmu m and 200 upmu m reduce the critical N-factor in the range of varDelta N approx 1.5 pm 1. Interestingly, an increase in gap width from 100 to 200 upmu m was not found to induce smaller transition Reynolds numbers or reduced N-factors, which might be due to resonance effects.

Downstream characteristics of extended flat plate trailing edge on S809 wind turbine blade under various turbulent intensities

Purpose This study aims to investigate the effect of downstream characteristics of S809 wind turbine blade with various extended flat plate (EFP) configuration. Wind farms are recently modified to improve the power production through placing number of wind turbines and locations. Design/methodology/approach A series of wind tunnel experiments were carried out to evaluate the downstream wake characteristics of the S809 airfoil attached with various EFP (EFP, A = 0.1C, 0.2C and 0.3C) at various angles of attack corresponding to free stream velocity Reynolds number (Re) = 2.11 × 105 and various turbulence intensity (TI = 5%, 7%, 10% and 12%). Findings For the S809 wind turbine blade attached with EFP, the downstream velocity ratio decreases with increasing in angle of attack and the velocity deficit decrease with increasing turbulence intensity (TI) up to TI = 10%. The wake intensity for the S809 wind turbine blade and S809 airfoil with 10% of chord EFP performs the same for each downstream location. Practical implications Placing the wind turbine in the wind park next to another wind turbine poses a potential challenge for the park power performance. This research addresses the characteristics of the downstream turbulence intensity profile modified with the EFP in the wind turbine blade which improves the downstream characteristics of the turbine in the wind park. Originality/value The downstream velocity ratio decreases with increasing angle of attack and the velocity deficit decrease with increasing turbulence intensity (TI) up to TI = 10%.

Flow and acoustics in a model rocket flame deflector and deflector cover

The design of a rocket launch environment is a complex process with many different aspects that are highly interconnected. Acoustics, which is one of these, should be investigated in detail due to possible devastating effects on the launch vehicle, crew, and launch environment. This study uses a numerical method to consider a passive noise reduction method applied to a supersonic jet impinging on an inclined flame deflector to decrease the acoustic loads on the launch vehicle and noise levels in the far-field. In a supersonic jet impinging on an inclined flat plate configuration, acoustic waves that travel upstream originate from the impingement and wall jet regions. These upstream traveling waves are a combination of the acoustic waves that are produced by the high speed jet flows in the wall jet region and acoustic waves that reflect from the impingement wall. Due to the inclination of the impingement plate, these waves either travel to the far-field in the upstream direction or travel towards the free-jet region interacting with the high speed flow near the nozzle lip. This interaction can create a self sustaining feedback loop, which can cause acoustic tones to appear in the near- and far-field spectra. It is the aim of the present study to block the upstream traveling waves by introducing a second inclined wall with a circular cut-out between the nozzle exit and the impingement plate. Different configurations with different wall locations and cut-out sizes are investigated using a Detached Eddy Simulation CFD solver and an acoustic solver that is based on the Ffowcs Williams and Hawkings analogy. The mechanisms for the establishment of the feedback loops are examined.

Efficient Global Optimization of a laidback fan-shaped cooling hole using Large-Eddy Simulation

In the film cooling technique, cold fluid exiting from holes on the surface of the turbine creates a protective film which prevents the ruin of the solid material composing the blades. It is now known that the hole geometry is a key element of this approach and determines the adiabatic film cooling effectiveness. The design of optimal holes which can operate at conditions of high-pressure turbines is, however, a challenge for which several research groups and industrial companies have invested in intensive numerical and experimental campaigns. In the present study, a Large-Eddy Simulation based approach is adopted and demonstrated to be able to optimize the shape of a fan-shaped hole on a flat plate configuration in engine-representative conditions in static conditions, i.e. without rotation. The obtained results target high-pressure vanes and further studies are mandatory to investigate the effect of rotation for the application to turbine blades. This work is purely numerical as no experimental campaign has been done for such hot conditions. Nonetheless, the numerical setup used has been validated in a previously published studies. To do so, four main geometrical parameters defining such a cooling hole shape, namely the depth of the expanded section, the hole inclination angle and the forward as well as the lateral expansion angles are selected as design variables. The Bayesian based Efficient Global Optimization method along with the Expected Improvement as the acquisition function are used to find the maximum surface averaged film cooling effectiveness as the objective function. After nine database enrichment iterations needed to reduce the overall model error, an optimal shape for a given operating condition defined by the blowing and density ratios is obtained. Based on the response surface analysis, the effects of the design parameters on the adiabatic film cooling effectiveness are investigated. Finally, deeper analysis of the flow physics for four shapes is proposed to apprehend the role of the geometrical parameters on the fluid dynamics and on the adiabatic film cooling effectiveness.

Experimental investigation of thermal performance of single pass solar collector using high porosity metal foams

The previous literature showed that there have been many studies focusing on some specific aspects of single-pass solar air collectors, such as the effects of the number of passes, the shape of fins, and their effects on thermal performance. Also, the effect of thermal efficiency accompanied by the existence of these fins has been the interest of many studies. A few research types are dealing with using porous materials (Metal foam) to improve thermal performance. Therefore, an experimental apparatus was designed and fabricated to study the effect of Metal Foam (MF) on the performance of solar air collectors. The experiments were held in Iraq, Al Ramadi climate conditions. A comparison of three configurations of absorber plates of solar air heaters with and without MF is presented and evaluated. The results showed that by including MF fins in the absorber plate, the absorber plate's surface area was increased, increasing heat transmission compared to a flat plate (without MF). Moreover, utilizing MF at the tilted angle of 45° (MFθ=45o) increased turbulence intensity, which improved the mixing of cold and hot air. The MFθ=45o layout had the best thermal efficiency of the three employed configurations (94.8%), followed by the MFθ=0o configuration (62.6%) and the flat plate configuration (33.8%), all with the same mass flow rate. Finally, when using MF fins with a tilted angle of 45°, the air temperature differential is bigger compared to MF fins with a tilted angle of 0° or a flat plate collector.

Effects of Crescent Shaped Block Width and Length on Flow Field and Film Cooling Performance

Turbine blades and rocket nozzles can be efficiently protected from combustion chamber exhaust hot gases by film cooling technic. A crescent-shaped block placed downstream of the injection hole can significantly improve cooling effectiveness. The main objective of this research work is to investigate the influence of the crescent-shaped block length and width on film cooling effectiveness. ANSYS CFX was used to conduct analysis of a flat plate configuration with cylindrical holes. Nine configurations of the crescent shaped blocks were considered. For each case, the effect of blowing ratios (0.5 and 1) was investigated. The turbulence model shear stress transport (SST) is used for approximating turbulence. Good agreement was obtained by comparing the analysis results with the experimental data. The result indicated that block width variation has a considerable impact on film cooling performance. However, slight effect of block length on cooling effectiveness was obtained. Comparing all analyzed configurations, the best cooling effectiveness was reached for the model 9 (W = 3d, B = 1.5d). HIGHLIGHTS Rocket nozzles can be efficiently protected from combustion chamber exhaust hot gases by film cooling technic One of the latest techniques to optimize the overall performance of film cooling is adding an obstacle configuration downstream the coolant perforation Film cooling performance is considerably enhanced by placing a crescent shaped block downstream the injection hole The maximum enhancement in overall film cooling effectiveness using the optimal configuration (model 6: W = 2d, B = 1.5d) is about 252 % achieved at a blowing ratio of M = 1 GRAPHICAL ABSTRACT

Investigation of pressure feedback technique to control ramp based SWBLI

Shock wave boundary layer interaction (SWBLI) and associated boundary layer separation create undesirable phenomena such as enhanced aero-thermodynamic loads, localized turbulent spots, unsteadiness, drag enhancement, pressure recovery losses in high-speed flow applications. It necessitates an investigation on the control of shock-induced boundary layer separation. Therefore, a pressure feedback technique (PFT) to control the boundary layer separation has been studied numerically on a two-dimensional flat plate and ramp configuration. PFT consists of a channel that drains fluid from the separated region and reintroduces it in the core flow under the influence of pressure difference. The effect of various freestream, wall, and geometric conditions on the separation controllability of the PFT is examined. It has been observed that PFT with injection located near the upstream influence point and suction at the ramp foot reduces the length of the separation bubble by 12.15%. Variation of injection location marginally affects the separation reduction capability of PFT, while the performance of PFT is greatly dependent on suction location. The parametric study noted that the optimum suction location, for which the separation size is minimum, shifts downstream with increasing freestream Mach number, wall temperature, and ramp angle. Again the optimum suction location shifts upstream as freestream stagnation temperature to wall temperature ratio increases. Reynolds number is seen to have no impact on the optimum suction location. Moreover, freestream stagnation temperature to wall temperature ratio, which is a governing parameter in SWBLI studies, is also a relevant factor in the mechanism of PFT. Finally, the present limited investigation revealed that the suction end of the PFT positioned between Xsu/L = 1.12 to 1.194 provides a minimum size of shock-induced separation for varying freestream and wall conditions.

Unsteady mechanisms in shock wave and boundary layer interactions over a forward-facing step

The flow over a forward-facing step (FFS) at $Ma_\infty =1.7$ and $Re_{\delta _0}=1.3718\times 10^{4}$ is investigated by well-resolved large-eddy simulation. To investigate effects of upstream flow structures and turbulence on the low-frequency dynamics of the shock wave/boundary layer interaction (SWBLI), two cases are considered: one with a laminar inflow and one with a turbulent inflow. The laminar inflow case shows signs of a rapid transition to turbulence upstream of the step, as inferred from the streamwise variation of $\langle C_f \rangle$ and the evolution of the coherent vortical structures. Nevertheless, the separation length is more than twice as large for the laminar inflow case, and the coalescence of compression waves into a separation shock is observed only for the fully turbulent inflow case. The dynamics at low and medium frequencies is characterized by a spectral analysis, where the lower frequency range is related to the unsteady separation region, and the intermediate one is associated with the shedding of shear layer vortices. For the turbulent inflow case, we furthermore use a three-dimensional dynamic mode decomposition to analyse the individual contributions of selected modes to the unsteadiness of the SWBLI. The separation shock and Görtler-like vortices, which are induced by the centrifugal forces in the separation region, are strongly correlated with the low-frequency unsteadiness in the current FFS case. Similarly as observed previously for the backward-facing steps, we observe a slightly higher non-dimensional frequency (based on the separation length) of the low-frequency mode than for SWBLI in flat plate and ramp configurations.

Gas–liquid mixing in the stirred tank equipped with semi-circular tube baffles

Abstract Despite extensive contributions have been made over the past several decades, there are still ongoing challenges in improving gas dispersion performance in stirred tanks. To that end, a stirred tank equipped with four semi-circular (SC) tube baffles was designed. Hydrodynamics in the stirred tank before and after aeration were studied. The turbulent fluid flow was simulated using the standard k-ε turbulence model. The gas–liquid two-phase flow was simulated by the Eulerian–Eulerian multiphase model and the k-ε dispersed turbulence model. The impeller rotation was modeled with the multiple reference frame (MRF) approach. Firstly, the grid independence test was made. By comparing the distributions of gas holdup in the flat-plate (FP) baffled stirred tank with literature results, the reliability of the numerical model and simulation method was verified. Subsequently, the flow field, gas holdup and power consumption of the SC and FP configurations were studied, respectively. Results show that the former can increase the fluid velocities and promote the gas holdup dispersion. Besides, it is energy-saving and has a higher relative power demand (RPD). The findings obtained here lay a preliminary foundation for the potential application of the SC configuration in the process industry.

Light attenuation in enriched purple phototrophic bacteria cultures: Implications for modelling and reactor design

Light attenuation in enriched purple phototrophic bacteria (PPB) cultures has not been studied, and its understanding is critical for proper process modelling and reactor design, especially for scaled systems. This work evaluated the effect of different biomass concentrations, reactor configurations, wastewater matrices, and growth conditions, on the attenuation extent of near infra-red (NIR) and ultraviolet-visible (UV–VIS) light spectra. The results show that increased biomass concentrations lead to higher light attenuation, and that PPB absorb both VIS and NIR wavelengths, with both fractions of the spectrum being equally absorbed at biomass concentrations above 1,000 g COD·m−3. A flat plate configuration showed less attenuation compared with cylindrical reactors illuminated from the top, representative for open ponds. Neither a complex wastewater matrix nor the presence of polyhydroxyalkanoates (under nutrient limited conditions) affected light attenuation significantly. The pigment concentration (both bacteriochlorophyll and carotenoids) however, had a strong effect, with significant attenuation in the presence of pigments. Attenuation predictions using the Lambert-Beer law (excluding scattering) and the Schuster model (including scattering) indicated that light scattering had a minimal effect. A proposed mathematical model, based on the Lambert-Beer law and a Monod function for light requirements, allowed effective prediction of the kinetics of photoheterotrophic growth. This resulted in a half saturation coefficient of 4.6 W·m−2. Finally, the results showed that in dense outdoor PPB cultures (≥1,000 g COD·m−3), effective light penetration is only 5 cm, which biases design away from horizontal lagoons, and towards non-incident multi-panel systems such as flat plate reactors.

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

Abstract

A general modal frequency-domain vortex lattice method for aeroelastic analyses

The generalized aerodynamic force (GAF) matrix is derived for the Unsteady Vortex Lattice Method (UVLM) without the assumption of out-of-plane dynamics. As a result, the approach naturally includes in-plane motion and forces unlike the doublet lattice method (DLM). The derived UVLM GAF is therefore applicable to industry-standard techniques for aeroelastic stability analyses, such as the p–k method. In this work, the fluid–structure interpolation is performed with radial basis functions for surface interpolation. The generalized aerodynamic forces computed with the UVLM are verified against the DLM from NASTRAN on a simple flat plate configuration. The ability of the UVLM to include steady loads is verified with a T-tail flutter case and the results confirm the importance of including steady loads for T-tail flutter analysis. The modal frequency domain VLM therefore provides the same level of efficiency and accuracy than the DLM, but without the restrictions and with the ability to handle complex geometries. It is therefore a viable replacement to the DLM.

Effect of the Backward Facing Step on a Transverse Jet in Supersonic Crossflow

A transverse jet in the supersonic crossflow is one of the most promising injection schemes in scramjet, where the control or enhancement of jet mixing is a critical issue. In this paper, the effect of the backward facing step on the characteristics of jet mixing was investigated by three-dimensional large eddy simulation (LES). The simulation in the flat plate configuration (step height of 0) was performed as the baseline case to verify the computation framework. The distribution of the velocity and pressure obtained by the LES agreed well with the experiment, which shows the reliability of the LES code. Then, two steps with a height of 1.0D and 1.58D (D is the injector diameter) were numerically compared to the non-step baseline case. The comparison of the three cases illustrates the effect of the large-scale recirculation region on the variable distribution, and shock and vortex structures in the flow field. In the windward region, the shear layers become thicker, and the convection velocity of the shear vortexes reduces. In the leeward region, the wake vortices almost disappear while the counterrotating vortex pairs (CVPs) expand in the spanwise direction. In the area upstream of the jet, the separation bubble works with the upstream large-scale recirculation zone to entrain the jet into the upstream near-wall zone. At last, a comparison of the overall mixing performance of the three cases revealed that the penetration depth and mixing efficiency increased with the step height increasing.

Effects of dielectric gradients‐mediated ions partitioning on the electrophoresis of composite soft particles: An analytical theory

AbstractIn this work, we report original analytical expressions defining the electrophoretic mobility of composite soft particles comprising an inner core and a surrounding polymer shell with differentiated permeabilities to ions from aqueous background electrolyte and to fluid flow developed under applied DC field conditions. The existence of dielectric permittivity gradients operational at the core/shell and shell/solution interfaces is accounted for within the Debye–Hückel approximation and flat plate configuration valid in the thin double layer regime. The proposed electrophoretic mobility expressions, applicable to weakly to moderately charged particles with size well exceeding the Debye layer thickness, involve the relevant parameters describing the particle core/shell structure and the electrohydrodynamic features of the core and shell particle components. It is shown that the analytical expressions reported so far in literature for the mobility of hard (impermeable) or porous particles correspond to asymptotic limits of the more generic results detailed here. The impacts of dielectric‐mediated effects of ions partitioning between bulk solution and particle body on the electrophoretic response are further discussed. The obtained expressions pave the way for a refined quantitative, analytical interpretation of electrophoretic mobility data collected on soft (nano)particles (e.g., functionalized dendrimers and multilayered polyelectrolytic particles) or biological cells (e.g., viruses) for which the classical hard core‐soft shell representation is not appropriate.

Computational study on self-heating ignition and smouldering spread of coal layers in flat and wedge hot plate configurations

Porous fuels have the propensity to self-heat. Self-heating ignition has been a hazard and safety concern in fuel production, transportation, and storage for decades. During the process of self-heating ignition, a hot spot forms in the fuel layer and then spreads as a smouldering fire. The understanding of hot spot and smouldering spread is important for prevention, detection, and mitigation of fires. In this paper, we build a computational model that unifies the simulation of self-heating ignition and smouldering spread by adopting a two-step kinetic scheme obtained from literature. The model is validated against hot plate experiments of coal in both flat and wedge configurations. The comparison shows that the model predicts the minimum ignition temperature (Tig) and transient temperature profiles reasonably well. The simulation results demonstrate that the hot spot originates at the hot plate and then spreads towards the free surface due to oxygen consumption. In the wedge configuration, the simulations show that the height of maximum temperature point decreases with wedge angle, and that the influence of wedge angle can be explained by the heat transfer. This model brings together two combustion phenomena (self-heating ignition and smouldering) that were traditionally studied separately and analyses the transient behaviour of hot spot and smouldering spread in detail. It deepens our understanding of self-heating fire and can help mitigate the hazard.