Forced Flow Research Articles

Influence of bank slope on sinuosity-driven hyporheic exchange flow and residence time distribution during a dynamic flood event

Abstract. This study uses a reduced-order two-dimensional (2-D) horizontal model to investigate the influence of the riverbank slope on the sinuosity-driven hyporheic exchange process along sloping alluvial riverbanks during a transient flood event. The deformed geometry method (DGM) is applied to quantify the displacement of the sediment–water interface (SWI) along the sloping riverbank during river stage fluctuation. This new modeling approach serves as the initial step focusing on the impact of the bank slope on the hyporheic exchange flux (HEF) and the residence time distribution (RTD) of pore water in the fluvial aquifer for a sinuosity-driven river corridor. Several controlling factors, including sinuosity, alluvial valley slope, river flow advective forcing and duration of flow, are incorporated into the model to investigate the effects of bank slope on aquifers of variable hydraulic transmissivity. Compared to simulations of a vertical riverbank, sloping riverbanks were found to increase the HEF. For sloping riverbanks, the hyporheic zone (HZ) encompasses a larger area and penetrated deeper into the alluvial aquifer, especially in aquifers with smaller transmissivity (i.e., due to increased hydraulic conductivity or reduced specific yield). Furthermore, consideration of sloping banks as compared to a vertical riverbank can lead to both underestimation and overestimation of the pore water travel time. The impact of bank slope on residence time was more pronounced during a flood event for high-transmissivity aquifer conditions, while it had a long-lasting influence after the flood event in lower-transmissivity aquifers. Consequently, the impact of bank slope decreases the travel time of water discharging into the river relative to base flow conditions. These findings highlight the need for (re)consideration of the importance of complex riverbank morphology conceptualization in numerical models when accounting for the HEF and RTD. The results have potential implications for river management and restoration and the management of river and groundwater pollution.

Solidity effects and azimuth angles on flow field aerodynamics and performance of vertical axis wind turbines at low Reynolds number

Solidity is an important parameter in the design, manufacture, and operation concerning energy yield and performance efficiency of VAWTs. This paper examined detailed aerodynamic analysis of solidity effects at constant Re and at low Reynolds numbers, the flow field and forces (lift, drag, and Torque coefficients) aerodynamics at various azimuth positions, and the changes in the performance and the flow field of VAWTs at a wide range of TSR. The simulation of two three-bladed VAWT configurations, σ = 0.26 (C = 0.03 m) and σ = 0.34 C = 0.04 m) over 1.5 ≤ λ ≤ 5.5 tip speed ratios on the CL, CD, CM, and speed were monitored and extracted, and the blades surrounding flow field is plotted from the CFD simulations. Performance (Cp -λ) curves, force hysteresis, and plots of the flow field for the turbines are matched at low λ = 2 5, high λ = 4, and Reynolds number to explain solidity effects on the VAWTs performance and aerodynamics thus providing good insight into the underlying aerodynamics for the differences in power coefficient between the two rotors in detail. This allowed the linking of the performance to the detailed force and flow field aerodynamics at various azimuth angles. It has been shown that the initiation of blade stall and stall vortices shedding started earlier on the σ = 0.26 VAWT than the σ =0.34 VAWT, thus affecting the force attained and ultimately limiting the rotor efficiency of σ = 0.26 compared with the σ =0.34 rotor and provided an improved understanding of solidity phenomenon that will help in the design, production and operation of VAWTs.

A black-box adversarial attack on demand side management

Demand side management (DSM) contributes to the industry’s transition to renewables by shifting electricity consumption in time while maintaining feasible operations. Machine learning is promising for DSM with reasonable computation times and electricity price forecasting (EPF), which is paramount to obtaining the necessary data. Increased usage of machine learning makes production processes susceptible to so-called adversarial attacks. This work proposes a black-box attack on DSM and EPF based on an adversarial surrogate model that intercepts and modifies the data flow of load forecasts and forces the DSM to result in financial losses. Notably, adversaries can design the data modifications without knowledge of the EPF model or the DSM optimization model. The results show how barely noticeable modifications of the input data lead to significant deterioration of the decisions by the optimizer. The results implicate a significant threat, as attackers can design and implement powerful attacks without infiltrating secure company networks.

Flow effects on sonochemical oxidation activity in a 20 kHz ultrasonic horn system

Forced fluid flow, when properly aligned with the geometry of a 20 kHz horn-type sonoreactor, can increase its sonochemical efficiency (SE). We designed a flow-through reactor configuration to evaluate the effect of fluid dynamics on sonochemical activity. Using particle image velocimetry (PIV), we mapped the velocity profiles within the sonoreactor under flow rates up to 350 ml/min, and ultrasound power density from 142 to 498 W/L. KI dosimetry and sonochemiluminescence (SCL) are conducted to correlate fluid motion with chemical activity.At an ultrasound power density below 241 W/L, placing the probe near the water surface with a 288 ml/min flow rate maximized radical generation. Conversely, above 402 W/L, maximum SE is achieved with the probe near the vessel’s bottom at the same flow rate. At power densities below 241 W/L, external flow increases the liquid residence time in acoustically active zones from 0.16 to an average of 6.3 s, yielding enhanced chemical activity. Above 402 W/L, the introduction of forced flow broadens the acoustic jet, relocating bubbles from the active zone below the probe’s tip to the area around its neck. The expansion of this active zone leads to increased SE.A significant discrepancy is noted between Electron Paramagnetic Resonance (EPR) and KI dosimetry in measuring hydroxyl (OH.) radical concentrations. EPR suggests that most of these radicals are lost to recombination, highlighting the rapid dynamics of radical generation and recombination into hydrogen peroxide (H2O2) at interfacial regions.

Computational Thermal-Fluid Dynamics analyses of borated water distribution in the Vacuum Vessel of the Divertor Tokamak Test facility

This work presents the full set of 3D Computational Thermal-Fluid Dynamics (CFD) analyses of the Divertor Tokamak Test (DTT) Vacuum Vessel (VV). The VV D-shaped double shell structure, divided into 18 Regular and Special sectors, is actively maintained at the operating temperature of 60 °C by borated water in forced flow to counteract the thermal loads and the heat transfer with the surroundings. Due to manufacturing and integration constraints, the different sectors cannot share the same design: the water will flow in the free space between the two shells composing the VV but, given the complexity of the geometry, a careful hydraulic design is mandatory, to avoid local stagnation points which may cause either overheating or freezing. The different hydraulic paths are separately analysed with the Star-CCM+ software, with a SST k−ω turbulence closure, proving the effectiveness of their design (pressure drop, temperature constraints and stagnation/backflow). In addition, the borated water mass flow rate distribution among the different paths is assessed. To conclude, results from CFD analyses are exploited to approximate the hydraulic characteristic of each sector and to develop a system-level model of the full VV with the Modelica language. The overall VV pressure drop of Δp=2810 Pa, the outlet mixing temperature of Tout,mix=333.06 K and a mass flow rate distribution close to the homogeneous condition (≈2.22 kgs−1 in each sector) confirm that no relevant issues are found in the current VV design from the thermal-hydraulic point of view.

A Sharp Version of the Benjamin and Lighthill Conjecture for Steady Waves with Vorticity

We give a complete proof of the classical Benjamin and Lighthill conjecture for arbitrary two-dimensional steady water waves with vorticity. We show that the flow force constant of an arbitrary smooth solution is bounded by the flow force constants for the corresponding conjugate laminar flows. We prove these inequalities without any assumptions on the geometry of the surface profile and put no restrictions on the wave amplitude. Furthermore, we give a complete description of all cases when the equalities can occur. In particular, that excludes the existence of one-sided bores and multi-hump solitary waves. Our conclusions are new already for Stokes waves with a constant vorticity, while the case of equalities is new even in the classical setting of irrotational waves.

ANALYSIS OF THE PERFORMANCE OF A JOINT THAT COMBINES HIGH-STRENGTH BOLTS AND WELDING

In steel constructions, sometimes, it is necessary to combine bolts and welds in a single joint. While some design provisions for these combination joints appear in current standards, there have been no design rules generally verified by physical tests. In addition, the rules appear illogical in some cases, possibly leading to unconservative designs. The need for a combined joint in steel structures can arise for several reasons. For example, load requirements for an existing bolted joint may change, necessitating the joint redesign. As a result of bolt clearance requirements or limitations due to the existing joint plate size, there may not be sufficient space to add more bolts. Also, drilling a new bolthole in the field may not be possible because of space restrictions. For this situation, adding welds to the joint is the only practical option to give the joint the necessary increase in load resistance. The need for a combination joint may also arise in new construction. Another situation often requiring a combination joint is repairing a riveted joint. The assumption that the ultimate strength of a connection is the sum of the ultimate strength of each mechanical fastening element present in the connection is an unconservative approach to the design of the connection. In contrast, only accounting for the ultimate strength of one of the individual types of mechanical fastening elements in a combination joint is a very conservative approach. In the design of steel structures, it may be necessary to use a combined joint in which bolts and welds take up the force flow. Guidelines for the design of such a combined joint are available in the current DBN B.2.6-198:2014 ‘Steel structures. Design standards’. However, there are no practical examples and recommendations for calculating this type of joint in the scientific and technical literature. This article is devoted to studying the combined joint to improve understanding of the nature of its operation. The authors achieved the goal by numerical modelling of combined joints. Numerical experiments have shown that the welds’ orientation and the bearing capacity of bolts are two key factors to consider when determining the proportion of force acting on welds and bolts. Keywords: high-strength bolt, welds, combined joint, stress-strain state.

Carboxymethyl cellulose-water-based hybrid nanofluid mixed convection flow between porous vertical plates: Entropy generation analysis

This paper analyzes the thermodynamic second law analysis of mixed convection heat transfer of Carboxymethyl Cellulose (CMC)-water based viscoelastic hybrid nanofluid flow in a vertical parallel plate channel filled with porous medium. In mixed convection flow, where both buoyancy and viscous forces play significant roles in the flow behavior, the inclusion of viscous dissipation in the analysis is crucial. The governing equations of the problem are converted into a system of ordinary differential equations using appropriate similarity transformations, which are then solved by the Homotopy Analysis Method (HAM). The behavior of non-dimensional velocity, temperature, skin friction coefficient, Nusselt number, entropy generation and Bejan number profiles for a range of pertinent flow parameter values is displayed graphically and deliberated. Study reveals that a decrease in the dominance of viscous forces relative to inertial forces within the porous medium lowers entropy generation in the system.

Experimental study on local scour protection and contact pressure of the facing water surface at the pier based on the guide pillar

The safety of pier foundations is an important issue in bridge construction, where local bridge scour is a major cause of bridge damage worldwide, exacerbated by ice sheets. This paper offers a live bed scour experimental investigation that assesses the impacts of the new anti-scour device guide pillar of different sizes on geometric properties of scour, downflow velocity distribution, and turbulence intensity around the pier under different flow velocities and roughnesses, and to select the optimum installation position and size of the guide pillar. The results demonstrate that the guide pillar has a considerable effect on the scour hole and downflow around the pier, and the maximum reduction rate of scour depth is 59.3% in the optimal installation position (2d). By arranging distributed thin-film pressure sensors on the pier and measuring the pressure distribution on the facing water surface of the pier and the position of the center of gravity, this paper analyzes the distribution characteristics of the water flow force on the pier and the impact resistance of the guide pillar to the pier scour. The study found that the guide pillar reduces the water flow force by 61.3% without considering the effect of hydrostatic pressure.

Assessment of lung function variability documents airflow limitation in many patients with long covid

BackgroundIt is estimated that 65 million people worldwide suffer from long covid (LC). Many LC symptoms are also reported by patients with airflow limitation, used to confirm asthma. The primary aim was to detect airflow limitation in LC patients by a methacholine bronchial provocation test (BPT) and if negative, by evaluation of diurnal variability in forced expiratory flow in 1 second (FEV1) over a two-weeks’ period. The second aim was to assess responsiveness to asthma treatment on diurnal FEV1 variability and LC symptoms. MethodsPatients with LC for at least six months were recruited in this open diagnostic study. Burden of LC symptoms were reported on a 10-point Likert scale (0 = not troubled, 10 = extremely troubled) at inclusion and after three weeks’ asthma treatment. A positive methacholine BPT was defined by an accumulated provocation dose (PD20)<8 μmol causing 20% fall in FEV1. App-based spirometer was used for diurnal FEV1 variability, deemed positive by diurnalvariability in FEV1 ≥12%. ResultsAirflow limitation was documented by positive methacholine BPT in 8/30 (27%), or by excessive diurnal variability in FEV1 in 21/22 (95%) of the BPT negative LC patients. One patient dropped out due to personal issues. Three weeks’ asthma treatment normalised mean diurnal FEV1 variability from 18.0% to 7.3%, p < 0.001. Significant reductions were observed for fatigue and dyspnoea, from 8.3 to 6.1, p < 0.001, and 3.0 to 0, p < 0.001, respectively. ConclusionThis study indicate that airflow limitation may be detected in many LC patients if evaluation of diurnal variability in FEV1 is included in the diagnostics.

Hydrodynamic force and torque models for cylindrical particles in a wide range of aspect ratios

During the pneumatic conveyance of biomass in a coal-fired power station boiler, biomass particles have cylindrical shapes with different aspect ratios. They move through the fluid at any angle and rotate strongly. However, highly accurate and general models of the drag, lift, and torque coefficients (CD, CL, and CT) for biomass particles in a wide range of aspect ratios, especially the CT model and the high aspect ratios, are currently lacking. This paper presents detailed direct numerical simulations of the flow around cylindrical cylinders with varying aspect ratios (6 ≤ AR ≤ 22), Reynolds numbers (100 ≤ Re ≤ 2000), and angles of incidence (0° ≤ θ ≤ 90°). The simulation was conducted using the OpenFOAM solver with the body-fitted mesh method. The flow characteristics and force coefficients of cylindrical particles with different AR were systematically analyzed. New functional correlations between CD, CL, and CT and AR, Re, and θ values were established. The mean squared errors for CD, CL, and CT were 8.8 × 10–2, 2.4 × 10–2, and 4.7 × 10–2, with average relative errors of 5.8%, 3.5%, and 8.17%, respectively. A comparison of the results with other experimental and simulation data in previous literatures showed that the new CD and CL models have considerable higher predictive ability. The generality of the new CD model expanding to low ARs of 1.5 and 3 is verified finally. The new force and torque models are expected to improve the accuracy of Eulerian–Lagrangian simulations of various cylindrical particle-laden flows in the utility of biomass energy.

Dynamic performance prediction and experimental analysis of wet clutch actuator considering thermal flow characteristics

The hydraulic actuator system (HAS) for wet clutches in heavy-duty vehicle transmissions is required to have a fast response and high precision in the pressure regulation procedure. Conventional pressure control valves for HAS are almost slide spool structures, which perform a large flow force at a high flow rate. An open-center spool structure is designed and developed in this paper, which is a combination of a traditional slide spool and a valve sleeve. It has an orifice-groove combination throttling orifice, which can take into account the large through-flow capacity and small flow force. Firstly, to deeply understand the mechanism of pressure variation in the clutch chamber, a high-fidelity dynamic characteristic mathematical model of HAS considering the oil temperature is proposed. Secondly, the functional relationship between the oil temperature on the medium physical property parameters and the orifice thermal flow parameters in the model is deduced in detail. An experimental bench to measure the pressure valve dynamic performance and actuator pressure regulation characteristics in a wide temperature domain is then designed and implemented to validate the accuracy of the simulation model. Finally, the mechanisms of oil temperature and system pressure on pressure impact and pressure response are quantitatively analyzed in association with a supervised learning algorithm. The feasible domains of the two adjustable variables are also explored. This study provides a new perspective on dynamic control and energy saving of HAS pressure valves and a new method for the prediction of HAS performance under complicated operating conditions.

Quenching extinction of solid sphere diffusion flames induced by a sudden removal of gravity

The response of a diffusion flame around a PMMA solid sphere to a sudden transition to zero-gravity is investigated both experimentally and numerically. The initial flame is established in normal gravity with a low speed forced flow in a 17% oxygen by volume atmosphere. An abrupt (step change) normal-to-zero gravity transition occurs when the test package is released in the drop tower. The dynamic flame response is recorded by video and modeled numerically. By the end of the 5.18-s drop, the flame tip retreats, and the flame base may either remain stabilized near the forward stagnation region or extinguish depending on several parameters. The two parameters investigated are: forced flow velocity and the degree of preheating in the surface layer of the solid sample. The amount of preheating or equivalently the conductive flame heat loss rate to the solid interior is varied by controlling the duration of the normal gravity burning before releasing to microgravity. The heat loss is quantified by using embedded thermocouples to measure the solid subsurface temperature gradient near the stagnation point. The detailed numerical model reveals details of the flow field and flame structure including oscillatory extinction and quantifies the various transient gas-solid surface energy balance terms.

Adjustment of Proportional Control Valve Characteristics via Pressure Compensation Using Flow Forces

This article concerns flow analysis through a multi-section proportional control valve. In valves of this type, the flow rate is adjusted through an electromagnet current. However, for a fixed control signal value, the flow rate changes as the pressure in the system increases, which is an unfavorable phenomenon. Compensation for pressure influence is usually achieved using additional valves. In this work, the valve characteristics were modified to achieve a possibly steady flow rate by compensating for the pressure using flow forces without the necessity of correction valves. For this purpose, the geometry of the spool throttling slots was designed by making precise cuts. Moreover, the parameters of the return springs were adjusted accordingly. The changes were introduced in such a way as to adjust the direction of the fluid stream and thus influence the balance of forces acting on the spool. Simulation tests were performed using the CFD method. In turn, laboratory experiments were carried out using the PONAR WREM10 valve with a prototype spool in two neutral position flow configurations: closed (E) and open (W). The results confirmed the valve’s ability to maintain a quasi-constant flow rate in a wide pressure range. The maximum obtained non-uniformity in the flow rate for the fixed control signal in the whole studied pressure range, p = 5–30 MPa, was 6.3% except for the lowest current intensity, I=0.6A, when it raised to 13.6%. Moreover, high consistency between simulation results and laboratory experiments was achieved. The difference in the obtained flow rate did not exceed 8–10% in the case of low current intensity values I=0.6–0.75 A, and it fell below 5% at higher ones.

Experimental and numerical studies of the effect of perforation configuration on heat transfer enhancement of pin fins heat sink

AbstractIn this study, experimental and computational studies of the impact of forced convective flow on the heat transfer characteristics of staggered pin fins with perforations are investigated in a rectangular channel at constant heat flux with Reynolds numbers (Re) of 2 × 103–12 × 103. In particular, cylindrical pin fins with circular longitudinal (L) perforation, longitudinal/transverse (LT) perforation, and longitudinal/transverse/vertical (LTV) perforation perforations are compared to solid pin fins to find out how adding different perforation arrays affects overall heat transfer performance and also to find the best perforation configuration for maximum performance. ANSYS‐FLUENT is employed for numerical simulation, validated by experimental data. Experimental validation is conducted by attaching the heat sink to a Peltier module, inducing heat generation through current on one face in the Armfield Free and Forced Convection Heat Transfer Service Units HT 19 and HT10XC. Results highlight significant increases in Nusselt number (Nu) for perforated pins compared to solid pins, with L perforations at 8%, LT perforations at 33%, and 67% for LTV perforated pins due to transverse perforations that act as slots, which stir up the primary flow and induce secondary flow generated by vertical perforations. Regarding pressure drops, L perforations reduce by 9%, LT by 19%, and LTV by 27% compared to solid pins. The overall enhancement ratio peaks at the minimum Reynold number, notably achieving a 38% increase in the LTV perforation pin fin array. This innovative study holds promise for diverse electronic applications, offering enhanced heat transfer performance in electronic cooling systems.

A Numerical Study on the Performance of a Pumping Station with Bell-Mouth-Based Vertical Pumps during an Accidental Shutdown

This study presents a numerical simulation of a pump’s performance during a power-cut event and connected hazards resulting from the failure of non-return flap valves. The vertical mixed-flow pumps with suction bells were mounted inside the suction basins of a pumping station. Different regimes of the pump operation during the time were analyzed based on the pump’s 4-quadrant characteristics and the dynamics of rotating parts in the pump, gearbox and electric engine. The resulting development of flow rates, rotor speed and forces in the course of time were used to analyze the hazards of failure of any pumping system component and the flooding of the suction object and its surroundings. The presented results show a deep insight into the flow phenomena in vertical mixed-flow pumps with suction bells during the runaway process and confirm that the developed methodology can be successfully applied to monitor the critical regimes in a pumping station in real time. The simulations were verified with some experimentally obtained data.

Effect of the Flow Passage Area Ratio on a Double Slit-Type Pintle Injector

Due to the structural characteristics of the pintle injector, a recirculation zone is generated under the pintle, so the pintle tip is directly exposed to a high-temperature environment. Therefore, the cooling technique and protective coating on the pintle tip are essential for improving the reusability and durability of the pintle injector. Although various cooling methods are known, this study applied a forced flow passage cooling method by adding internal structures called inserts to the pintle injector. The characteristics of the insert were analyzed experimentally and numerically based on change of its area ratio. When the internal flow changes, the spray angle, droplet size, and cooling performance also change in accordance with an increase in the insert’s central area. When the insert structure is installed in the pintle post, upward flow may occur, which can worsen the spray angle and droplet distribution characteristics. Nevertheless, owing to the insert structure, the surface temperature of the pintle post is reduced dramatically as intended. Thus, an optimal design technique for cooling by changing the area ratio of the first- and second-row slits of the pintle post can be suggested to overcome the limitations of the insert structure. The results of this study will be helpful in understanding the spray characteristics of the insert structure and optimize the design of cooling channels for reusable pintle injectors in the future.

On the Solution of Blasius Boundary Layer Equations of Prandtl-Eyring Fluid Flow Past a Stretching Sheet

Objective: This paper investigates velocity profile for two-dimensional, incompressible, laminar forced convection flow of the fluid model for Prandtl-Eyring fluid past a stretching sheet in the presence of fluid parameters. Methods: The governing partial differential equation for the flow was transformed into non-linear ordinary differential equation by using the deductive one parameter group theoretic method and numerical solution of non-linear ordinary differential equation (ODE) is solved by MATLAB bvp4c solver. Findings: The solution of velocity profile obtained as a function of parameter and . The effect of the fluid parameter was discussed graphically. Novelty: The main goal of this article is to analyze boundary layer flow of Prandtl-Eyring fluid over a stretching surface. The conservation equations of mass, momentum are converted into non-linear ordinary differential equations along with boundary conditions using deductive one parameter group theoretic method and solved by MATLAB ODE solver. Comparisons with previously published works are made, and results show a high level of agreement. This type of research is applicable to extrusion, paper production, fiber glass production, hot rolling, condensation process, crystal growing, polymer sheets etc. Keywords: Boundary layer, laminar flow, Deductive one parameter Group theoretic method, Absolute invariant, Stretching Sheet, Prandtl-Eyring fluid

Mebendazole preferentially inhibits cilia formation and exerts anticancer activity by synergistically augmenting DNA damage

The cilium is a microtubule-based organelle that plays a pivotal role in embryonic development and maintenance of physiological functions in the human body. In addition to their function as sensors that transduce diverse extracellular signals, including growth factors, fluid flow, and physical forces, cilia are intricately involved in cell cycle regulation and preservation of DNA integrity, as their formation and resorption dynamics are tightly linked to cell cycle progression. Recently, several studies have linked defects in specific ciliary proteins to the DNA damage response. However, it remains unclear whether and how primary cilia contribute to cancer development. Mebendazole (MBZ) is an anthelmintic drug with anticancer properties in some cancer cells. MBZ is continuously being tested for clinical studies, but the precise mechanism of its anticancer activities remains unknown. Here, using Xenopus laevis embryos as a model system, we discovered that MBZ significantly hinders cilia formation and induces DNA damage. Remarkably, primary cilium-bearing cancer cells exhibited heightened vulnerability to combined treatment with MBZ and conventional anticancer drugs. Our findings shed light on the specific influence of MBZ on cilia, rather than cytosolic microtubules, in triggering DNA damage, elucidating a previously unidentified mechanism underlying potential MBZ-mediated cancer therapy.

Unsteady Lift Produced by a Flat-Plate Wing Translating Past Finite Obstacles

The unsteady lift of a high-angle-of-attack, flat-plate wing encountering finite-length obstacles is studied using towing-tank force measurements and flow visualization. The wing translates from rest and at 1 chord traveled interacts with a rectangular channel, ceiling, or ground. The angle of attack, obstacle length, and height to the obstacle are varied. As the channel gap height decreases, circulatory-lift peaks attributed to leading-edge vortices (LEVs) become larger, and for the second peak onward occur earlier, from wing blockage enhancing the flow speed. Larger and earlier LEVs are visualized, supporting this, as are secondary vortices off the channel. The lift reduces while exiting a channel, being lowest afterward if exiting during a lift peak. For ceilings, the first circulatory-lift peak increases for smaller LE-to-ceiling gaps, but for 0.5 chord gaps or less, later maxima are below the no-obstacle case yet still earlier. For grounds, with lower wing height the first circulatory-lift peak is larger but the second peak’s behavior varies with angle of attack, and lift decreases near the ground end. Grounds affect peak timing the least, indicating less influence on the LEV. The lift rises slightly ahead of channels and ceilings, and often lowers before channels and grounds end, providing warnings.