This numerical study presents laminar, two-dimensional analyses of unconfined flow over two staggered square cylinders, oriented at a 45° angle relative to the incoming flow direction. The investigation examines six center-to-center gap spacing: S = 2D, 3D, 4D, 6D, 8D, 10D, and 12D, where D indicates the side length of the cylinders. The study covers a broad range of Reynolds numbers (Re), from 1 to 200, encompassing creeping, steady, and unsteady flow regimes. The primary objective is to assess the effects of both Re and S/D on flow patterns and associated quantities. Furthermore, the impact of computational domain size on the results for varying Re is examined. Another aim is to determine the critical Reynolds numbers (Recr) that trigger the onset of vortex shedding. The findings reveal that as S/D increases, Recr rises, gradually approaching the Recr value associated with a single cylinder. Four distinct time-averaged flow patterns are identified based on streamlines analysis. Generally, the downstream cylinder exerts a controlling influence on the flow dynamics of the upstream cylinder, while the upstream cylinder enhances vortex shedding from the downstream counterpart. The impact of Re and S/D on comprehensive aerodynamic characteristics is attributed to their contributions to determine the flow regime and pattern, the degree of vortex merging occurring behind the cylinders, and the flow intensity in the interstitial space. However, the significance of S becomes less pronounced for inter-cylinder distances exceeding 4D, due to diminished mutual interaction effects between the flows passing around the cylinders.

To examine the flow characteristics of horseshoe vortices (HV) in wall-mounted rectangular cylinders, surface oil-flow visualization and Large Eddy Simulation (LES) were used for experimental and numerical studies, respectively. This research examined various incident angles relative to the approaching flow (LES: alpha = 0 degrees-45 degrees, oil-flow visualization: alpha = 0 degrees-90 degrees) and cross-sectional aspect ratios (CR = 1-4) for Reynolds numbers of (12 48) x 103. The features of HV have been analyzed, and the critical points (saddle and focal) and their relationships to physical phenomena have been evaluated. The presence of two saddle points (S1 and S2) and their associated nodes (N1 and N2) confirms the formation of two regions in the horseshoe vortices. The region closer to the upstream of the cylinder experiences higher shear stress than that farther away. It was observed that two focal points appear behind the cylinders, which show the positions of arch-shaped vortex legs that meet the bottom surface. Three patterns of horseshoe vortices were identified based on the focal point positions for various alpha and CR. The focal points in pattern I are symmetric with respect to the streamwise direction, where their spacing is less than the width of the cylinder. In pattern II, the focal points lose symmetry, forming on one side of the cylinder very close to each other. The positions of focal points in pattern III become asymmetric with respect to the streamwise direction. In addition, the width of the HV region and the reattachment point on the cylinder surface were examined for different CR and alpha. The reattachment point occurs at the junction between cylinders and wall for CR = 4 at alpha = 0 degrees-15 degrees, CR = 3 at alpha = 5 degrees-15 degrees, CR = 2 at alpha = 10 degrees-15 degrees, and CR =1 only at alpha = 15 degrees.

This study investigates the three-dimensional (3D) wake transition in unconfined flows over rectangular cylinders using direct numerical simulation (DNS). Two different cross-sectional aspect ratios (AR) and Reynolds numbers (Re) are scrutinized: AR = 0.5 at Re = 200 and AR = 3 at Re = 600. The investigation focuses on characterizing the flow patterns and forecasting their temporal evolution utilizing the proper orthogonal decomposition (POD) technique coupled with a long short-term memory (LSTM) network. The DNS results reveal the emergence of an ordered mode A for AR = 3, attributed to the stabilizing effect of the elongated AR. On the other hand, the case with a smaller AR (= 0.5) exhibits a mode-swapping regime characterized by modes A and B's distinct and simultaneous manifestation. The spanwise wavelengths of mode A and mode B are approximately 4.7 and 1.2 D for AR = 0.5, while the spanwise wavelength of mode A is 3.5 D for AR = 3. The POD serves as a dimensionality reduction technique, and LSTM facilitates temporal prediction. This algorithm demonstrates satisfactory performance in predicting the flow patterns, including the instabilities of modes A and B, across both transverse and spanwise directions. The employed algorithm adeptly predicts the pressure time series surrounding the cylinders. The duration for training the algorithm is only about 0.5% of the time required for DNS computations. This research, for the first time, demonstrates the effectiveness of the POD-LSTM algorithm in predicting complex 3D instantaneous wake transition patterns for flow past rectangular cylinders.

The present work studies the flow sheltering effect over two tandem non-identical-height wall-mounted square cylinders (buildings-like structures with aspect ratios of AR=4 and 7) via Large Eddy Simulation (LES) at Reynolds number (Re=ρUDμ) 2.2×104. The gap and wake flow dependencies on two opposite flow directions, where the oncoming flow first reaches the shorter cylinder for Geo.1 (at wind angle of 0°) and vice versa for Geo.2 (at wind angle of 180°), are examined for the scaled gap spacings (G*=G/D) of G*=1,3,5 at different heights of the prisms (z*=zD=1.0,2.0,3.5,5.0,6,5). It is found that the sheltering effect is contingent on inflow direction and G*, and determines the presence or absence of seven identified flow regimes, named slender-body, alternate reattachment, semi-stable gap, co-shedding, solo-shedding, and symmetric shedding. Then, the correlation of the sheltering effect and the flow topology, and subsequently, the wall pressure distribution, aerodynamic forces, and vortex shedding are discussed. The paper further comments on the practicalities associated with urban aerodynamics, i.e., pedestrian-level wind conditions, and aerodynamics interfering factor (AIF). It is found that the pressure distribution on the cylinders’ walls is strongly dependent on the gap flow structures and the inflow direction for both configurations (Geo.1 and Geo.2). Therefore, the mean drag, lift, and drag force fluctuations and aerodynamic interference factor (AIF) of these forces are dependent on G*, increasing with an increase of G*. Regardless of the inlet flow direction and G*, the minimum gap spacing to provide suitable aerodynamic comfort in the wake and the gap on the pedestrian level is G*=3.

The fluid flow and heat transfer are investigated in high-performance heat exchangers with Schwarz-P and Gyroid structures using numerical and experimental approaches. This study was carried out first for laminar flow (Re = 10-100, Pr = 3-6) numerically and second for turbulent flow (Re = 1850-5500, Pr = 3.5) numerically and experimentally. All simulations were performed with COMSOL software to investigate the flow patterns, thermal performance, and pressure drop in heat exchangers based on the Schwarz-P and Gyroid with various unit cell numbers between 1 and 64. For low Re simulations, it is observed that the heat transfer coefficient and performance evaluation coefficient (PEC) increase with increasing the number of cells (or decreasing the cell size) in a constant volume. By redefining the Reynolds number based on the hydraulic inlet diameter and the velocity at the inlet of the structure, the Colburn and friction coefficients become independent of the structure's density. Correlations are provided to predict these coefficients. The results show that the Gyroid with 64-unit cells provides an average of 24 % (maximum 33 %) enhancement in the PEC and 40 % (maximum 46 %) Nusselt number improvement over the tube banks. On the contrary, the Schwarz-P does not have an improvement in PEC or Nusselt number compared to the tube bank. For the high Re study, several prototype heat exchanger samples based on the Schwarz-P and Gyroid structures were fabricated utilizing the FDM 3D-printing technique with no support structures to show that these heat exchangers could be manufactured. The SLM method was also used to fabricate a Gyroid heat exchanger for use in the experimental studies. The performance of a Gyroid heat exchanger made of AlSi10Mg has been tested for input flow rates ranging from 1 to 3 L per minute. For numerical simulation, the k-epsilon and K-W-SST turbulence models are employed and their results are compared with the present experimental data. It is found that the results of the K-W-SST model provide better agreement with experimental ones.

Numerical simulations are conducted to analyze flow characteristics around two tandem sharp-edged cylinders with cross sections of square (b*1 = 1) for the upstream cylinder and rectangle (b*2) for the downstream cylinder (b* = b/a, where a and b are the sides of cylinders). The study investigates the effects of Reynolds numbers (Re = 30 - 150), cross-sectional aspect ratios of the downstream cylinder (b*2 = 1 - 4), and scaled gap-spacing between cylinders (S* = 1 - 6) on the flow structure, onset of vortex shedding, hysteresis and aerodynamic parameters. The results reveal that increasing b2* suppresses the vortex shedding of the upstream cylinder, depending on S*. The suppression is attributed to the interference effect and the adhesion of the shear layers on the downstream cylinder. Three distinct time-mean flow patterns are identified based on the separation and reattachment of shear layers. The first flow pattern (I) exhibits parallel flow along the side faces of the upstream cylinder, while the separation bubbles associated with reattachment points are formed in flow pattern II on these faces. For pattern III, no reattachment point is observed and the separation bubbles cover the upstream cylinder' side faces. Additionally, two instantaneous flow patterns of extended-body and co-shedding are apperceived within the ranges of examined Re and S*. The behaviors of time-mean and varying forces as well as the vortex shedding frequency are correlated with the flow structures. The onset of vortex shedding and hysteresis dependence are discussed comprehensively. The results show that the critical Reynolds numbers for the onset of vortex shedding decrease from 128 to 50 with S* increasing from 1 to 6 (b*1 = 1 and b*2 = 4). The hysteresis limit is found within the range of 3.5 < S* < 4.5 for flow over two tandem cylinders (b*1 = 1 and b*2 = 4) at Re = 150.

In this paper, numerical investigations are carried out to examine the laminar fluid flow and heat transfer characteristics of three various base fluids, six different water-based mono nanofluids, and six types of hybrid nanofluids (five binary and one ternary types) in a rotating U-shaped microchannel. In addition, the entropy generation is determined in microchannel for Cu/water nanofluid and pure water using both constant wall temperature (CWT) and constant heat flux (CHF) boundary conditions. This is accomplished using an Eulerian–Eulerian two-phase model for nanofluid simulation. In fact, this study aims to determine the impacts of various base fluids and nanofluids, Reynolds number (Re = 200–900), rotational speed (0–600 rad/s), and thermal boundary conditions on the entropy generation, pressure drop, heat transfer enhancement, thermal performance coefficient, and so on. It is observed that water-based fluids have better performance in rotating and stationary microchannels in comparison with those of EG and EO fluids. A survey on the thermal performance coefficient and efficiency in stationary and rotating microchannels shows that all examined nanofluids perform better than pure water and the Cu/water and SiO 2 /water nanofluids have the best and worst thermal performances, respectively. Moreover, the combination of Al 2 O 3 and Cu nanoparticles with an equal volume fraction provides the highest Nusselt number compared to other types of nanofluids in rotating microchannel. The results show that the total entropy generation has a rising trend with increasing Reynolds number and rotational speed for CWT, while the contrary happens for CHF one. The total entropy generation of nanofluids is also lower than that of pure water in both CHF and CWT conditions. Finally, two correlations for total Nusselt number and friction factor are proposed that cover comprehensively all types of fluid examined.

In this study, the thermal and flow characteristics in a U-type microchannel have been investigated and compared under the influence of single and combined magnetic fields. The effects of various Reynolds numbers (Re=50-1000), Hartmann numbers (Ha=0-80), and nanoparticle volume fractions ( null =0.01-0.04) are examined. It is found that selecting the appropriate arrangement of applying single and combined magnetic fields plays an essential role in microchannel thermal performance and fluid flow behavior. Under the influence of some combined magnetic fields, a secondary flow is applied to the primary flow and affects the flow and heat transfer. The Nusselt number under the influence of the applied magnetic field(s) increases up to 137.7% or even decreases down to 25.5% compared to that without the magnetic field for various conditions. Results show that the combined magnetic fields usually provide better thermal performance than that of the single one.

The impacts of single- (SPM) and two-phase models (TPMs), including Euler-Lagrange (ELM) and Eulerian-Eulerian models (EEM), on a laminar forced convection heat transfer and fluid flow of the Al2O3/water nanofluid are evaluated in a rotating U-shape microchannel with a square cross-section and constant wall temperature. The effects of Reynolds numbers, rotational speed, volume fraction, Brownian motion, and implementation of no-slip and slip conditions are investigated. The slip velocity and heat transfer increase by increasing the volume fraction and rotational speed. The EEM and ELM provide a higher total Nusselt number than the SPM. The maximum heat transfer augmentations of 53.3%, 45.7%, and 41% are achieved for the EEM, ELM, and SPM by increasing the rotational speed from zero to 600 at phi = 5%. The predictions of pressure drop by TPMs are essentially the same but considerably lower than SPM. Unlike the ELM, the nanoparticle concentrations of EEM and SPM are uniform.

This paper studies the wake flow dynamics and heat transfer characteristics of two side-by-side finite wall -mounted square cylinders through large-eddy simulations at Reynolds and Prandtl numbers of Re = 1.2 x 104 and Pr = 0.7. The influence of normalized center-to-center distances between cylinders (S/d, where d is the side of the cylindersMODIFIER LETTER PRIME cross-section) is investigated for S/d = 2-5, while both cylinders pose an identical aspect ratio of AR = 7. First, the numerical approach is validated against the published experimental data. Then the instan-taneous and time-mean wake flow structures, as well as the global quantities, turbulence statistics and heat transfer are studied. It is found that the biased/flip-flop flow at S/d = 2 turns into anti-phase coupled vortex shedding flow at S/d >= 3. This flow regime transition induces a relatively sharp change in drag coefficient and vortex shedding frequency, minimum values at S/d = 2 and maximum values at S/d = 3. The Nusselt number mildly changes at S/d >= 3. The turbulent deflected gap flow at S/d = 2 results in inequality of drag forces on and heat transfer from two cylinders. That is, the drag coefficient and Nusselt number are larger for the cylinder towards which the gap-flow is deflected. It is also shown that swinging the deflected gap flow at S/d = 2 is a more intense source of turbulence than the vortex shedding from lateral faces, albeit the Reynolds stress is magnified with increasing S/d. The flow interference is steadily reduced with S/d, almost faded at S/d = 5.

This numerical study investigates the forced convection heat transfer from and flow topology around isothermal rectangular cylinders. The effects of various cross-sectional aspect ratios (AR = 0.25-4), Reynolds numbers (Re = 30-200), and Prandtl numbers (Pr = 0.7, 5) are examined on the results. Two or three-dimensional simulations are conducted depending on the Re and AR employed. The results show that the near primary vortices (K ' arm ' an wake) undergo a downstream transition to the two-layered vortices, followed by a transition from the two -layered vortices to the secondary vortices for AR <= 1. For smaller aspect ratios, the prevailing of the second-ary vortices is further accelerated, i.e., they emerge at a lower Re and a shorter downstream distance from the cylinder. Three types of secondary vortices distinguished based on their shape, strength, and generation mechanism were observed. A geometric criterion (spacing ratio) for the onset of evolution of the two-layer structure is proposed for each AR. It is observed that the sensitiveness of the Nusselt number to AR and Re can be ascribed to the change in the scenarios of the flow separation and reattachment (flow regimes), vortex strength, and wake-recirculation size (Lr). The Nusselt number grows with increasing Re and Pr but diminishes with AR. The relationship between the average Nusselt number and Lr is direct in the steady flow, while they are inversely linked in the two-and three-dimensional unsteady flow. Reducing AR from 4 to 0.25, depending on Re and Pr, leads to a 90%-170% enhancement in the Nusselt number, whereas increasing AR amplifies the total heat transfer due to an enlargement in the heat transfer surfaces. The second law of thermodynamics analysis reveals that cylinders with smaller AR generate lower entropy (destroy lower exergy); therefore, they are more efficient.

The features of flow fluid and convective heat transfer have been investigated numerically in a rotating rectangular U-shaped microchannel for various aspect ratios (AR). Pure water is used as working fluid and 3D steady simulations are performed for Reynolds number of 400. The effects of aspect ratio (AR = 0.25-4), slip/no-slip conditions, rotational speeds in the range of 0-300 rad/s on the velocity profiles/contours, heat transfer, pressure drop, Nusselt number, and thermal performance coefficient are studied. The results show that an increase in AR (for AR 1) or a decrease in AR (for AR<1) provided an increase in pressure drop and heat transfer. Besides, contrary to hydrophilic microchannel, the heat transfer and pressure drop decrease in microchannel with the hydrophobic surfaces for all ARs considered. In addition, the thermal performance coefficient (E) is used as a balance between heat transfer augmentation and the power consumed. It is found that the E is higher for microchannel with hydrophobic surface than that of with hydrophilic one for all ARs examined. Moreover, the rotating microchannel is more efficient in respect to heat transfer enhancement than that of the stationary case, especially at AR = 1. Moreover, the results for two thermal boundary conditions of constant heat transfer and constant wall temperature conditions are compared at AR = 1 and it is found that the total Nusselt number is higher for constant wall temperature case than that of constant heat flux case in rotating microchannel while it is contrary in stationary one.

The manipulation of the heat transfer and flow field using cylinder rotation is of a classical issue. It is of fundamental importance to study the dependence of wake and thermal topologies of two rotating cylinders in tandem arrangements. This study numerically investigates the time-resolved laminar flow, fluid forces, Strouhal number, and convective heat transfer over two isothermal co-rotating and counter-rotating circular cylinders in tandem arrangements for scaled cylinder center-to-center spacing S* = 2.5 - 6, non-dimensional rotational speed vertical bar alpha vertical bar <= 5, and Reynolds number Re = 100 - 200. How Re, S*, alpha and computational domain size influence the wake dynamics and thermal attributes is the focus of this study. The numerical procedure is validated against the available data in the literature for a single rotating cylinder. The influence of the blockage ratio on the single- and two-cylinder flow is determined first to decide the appropriate computational domain. It is found that rotating cylinders require a larger computational domain (blockage ratio approximate to 1%, when alpha > 2) than stationary cylinders (blockage ratio = 5%). The fluid forces are highly sensitive to the cylinder rotation when vertical bar alpha vertical bar > 2. Although both cylinders undergo the same magnitudes of time-mean drag coefficient vertical bar(C) over bard vertical bar or time-mean lift coefficient vertical bar(C) over barl vertical bar at a given lad, the cylinder rotation shifting from co-rotation to counter-rotation reverses the direction of (C) over bard, i.e. repulsive for the co-rotation and attractive for the counter-rotation. On the other hand, an increase in S* from 2.5 to 6 with alpha = 5 results in a 43% drag reduction for either cylinder. The S*, however, has an insignificant effect on (C) over barl (e.g. upto 5.3% at alpha = 5) while Re increases both vortex shedding frequency (e.g. 16.8% at alpha = 1) and heat transfer (e.g. upto 73.3% at alpha = 1). A flow map in a three-dimensional domain of S*, a and Re is provided, distinguishing steady and unsteady flows. Four distinct flow regimes are labeled, namely steady flow, alternate coshedding (AC) flow, single rotating bluff-body (SRB) flow, and inverted-rotation (IR) flow. An increase in vertical bar alpha vertical bar causes a modification of the AC flow to a steady flow and then to a SRB or IR flow. (C) 2021 Elsevier Ltd. All rights reserved.

This study aims to investigate experimentally the influence of rounding corners (r) as well as aspect ratio (AR) on the flow structures of a surface-mounted finite cylinder. The cylinders with sharp (r* = r/D = 0) and rounded corners (r*=0.167, 0.25 and 0.5) and aspect ratio or height-to-width/diameter ratio (AR = H/D) between 2 and 7 are utilized. The experiments are based on the five-hole probe and hot-wire measurements as well as the oil flow visualization. Wake measurements are made in an open return wind tunnel at the Reynolds number, Re = 1.6 x 104, where Re is defined based on the side width/diameter (D) of the cylinder cross-section and the freestream velocity. It is found that r* and AR have significant effects on the flow structure from the perspective of wake topology, strength of streamwise vortices, and vortex shedding frequency. For all r* considered, the wake is characterized by a quadrupole type (both the tip and base vortices are present) at AR = 7, while a dipole type occurs for AR = 2 and 4 (the base vortices are absent). The strength (circulation) of the streamwise vortex structures is affected by r*. For all AR examined in the present study, the strengths of tip and base vortex structures decrease with increasing r*. The oil flow visualization demonstrates that the features of the horseshoe vortex are sensitive to r* and AR. With increasing r*, the location of the separation line moves downstream and the distance between horseshoe vortex legs decreases. Velocity measurements reveal that the downwash flow enhances with increasing r*. It is also found that the Strouhal number increases progressively by 60% as r* increases from 0 to 0.5, regardless of AR.

Numerical simulations of two- and three-dimensional unconfined flows over rectangular cylinders are conducted at Reynolds number Re = 30 - 200. The cylinder cross-sectional aspect ratio AR (length-to-width) is varied as 0.25, 0.5, 1.0, 2.0, 3.0 and 4.0. The focus is given on how AR and Re influence the flow structure and associated aerodynamic parameters. The first critical Reynolds number (Re-cr1) associated with the transition from the steady flow to the two-dimensional unsteady flow is determined for each AR and found to linearly increase with increasing AR. The same observation is made for the second critical Reynolds number (Re-cr2) where the two-dimensional unsteady flow metamorphoses into the three-dimensional unsteady flow. A larger Re is required for a larger AR to have the onset of vortex shedding or the transition from two-dimensional flow to the three-dimensional. Three distinct scenarios of the flow separation and reattachment are identified in the ranges of Re and AR examined. The physical insight into the flow dependence on AR and Re is provided. Both AR and Re play a role in the formation of separation bubbles on the cylinder side surfaces. Two distinct mechanisms of the separation bubble formation are imparted. The detailed flow structures are linked to the mean and fluctuating forces and Strouhal numbers. The vortex strength beefs up with increasing Re but diminishes with AR, as do the normal and shear stresses and fluctuating forces.

This paper presents a dynamic thermal model which predicts the winding temperature of electrical machines at steady-state and transient conditions where windings are used in integrated battery chargers (IBCs) for DC charging in a stationary position. Using winding in high current charging process causes rising winding temperature which affects insulation life. Switched reluctance machines are a proper choice for using in electric vehicles (EVs) because of their advantages such as simple and sturdy structures. IBCs can reduce volume and weight of EVs and total cost is diminished because of integration. The analytical thermal model proposed in this paper can calculates the winding temperature in balanced and unbalanced currents injection because of the phase inductance in each rotor angle is distinct, so current excitation in each phase should be different for obtaining zero total torque and keeping rotor in a stationary position, also a reduced-order model is proposed with minor impact on the accuracy of the model. Special attention has been paid to monitor the winding temperature with considering the motor lifetime in DC charging mode, this view has not been addressed in IBCs before. The proposed model is then validated against experimental results and 3D finite element method.

The paper experimentally and numerically investigates the capability of the semi-cylindrical curved roofs in providing natural ventilation. Extensive measurements around a 1:17 scale model of a typical room with a semicylindrical roof have been conducted to determine the pressure and velocity field for gaining the discharge coefficients of apertures. Besides, smoke flow visualization and three-dimensional RANS simulations have been performed to correlate the ventilation characteristics, the induced volumetric airflow rate, and the flow trajectories. The prior studies were carried out on the domed roofs, but in the present study, the focus is on the semicylindrical curved roofs. It is found that the natural ventilation performance of the curved roof is profoundly sensitive to the wind angle (i.e. alpha) so that the extreme ventilation takes place at alpha = 0 degrees, while the alpha = 75 degrees - 90 degrees gives the lowest airflow rate. The dependence of the airflow rate on alpha is attributed to variation in the pressure difference between openings (known as the main driving force) caused by flow acceleration and flow separation. Further increase of alpha slightly ameliorates the airflow rate, although still not comparable with that of alpha = 0 degrees. Flow visualization results reveal that the height of the curved roof is a key factor in the enhancement of recirculation flow inside the building. Finally, a comparison discloses that the semi-cylindrical curved roof is prone to enhance the natural ventilation inside buildings as much as the wind-catchers, although presumably is cheaper in terms of the structural costs.

Wind tunnel measurement is conducted over two finite wall-mounted square cylinders in a staggered arrangement for various normalized cylinder distance (P* = P-s/d, where d is the cylinders width). For all experiments, two identical square cylinders with an aspect ratio of 7 are positioned on a line with a staggered angle of 45 degrees relative to the incoming flow direction. The mean pressure distribution on the surfaces of the cylinders, aerodynamic force coefficients and Strouhal numbers are obtained at a Reynolds number Re-d = 6 x 10(4) for 1.42 <= P* <= 5.7. Two flow regimes namely single-body (P* <= 2.1) and modulated-periodic (2.8 <= P* <= 5.7) are identified. The flow is also visualized using the smoke methods at P* = 4 to provide further verification on the modulated-periodic flow patterns. Both cylinders for the single-body regime shed vortices with the same frequencies, whereas the downstream cylinder in the modulated-periodic one represents three dominant frequencies in the spectral analysis. It is also observed that the downstream cylinder experiences a higher drag for P* >= 4.2.

Although the study of flow around buildings has a rich background, the development of construction material, the congestion of buildings, the urban ventilation and consideration of pedestrian wind condition make the necessity of further insightful flow-physic studies. This study numerically investigates the gap and wake flows associated with two inline non-identical-height (aspect ratios of 4 and 7 for the up- and downstream) buildings at a Reynolds number of 2.2 & times; 104 and gap spacing (G*) of 1, 3, and 5 through the large eddy simulation technique. It is found that an increase of G* mostly affects the flow pattern in the gap, so that the slender-body, alternate reattachment and semi-stable gap flow at the G* of 1 (or 3) turns into the co-shedding flow at the G* of 5. The pressure coefficients (Cp) on the cylinders' faces show that an increase of G* from 1 to 3 increases/decreases the Cp on the side (and top) faces of upstream/downstream cylinders, respectively. Further increasing G* from 3 to 5, however, drops the Cp on the side and top faces of both cylinders. On the other hand, the flow regime produces a profound effect on the pedestrian level so that the strong wind condition appears in the small gap, and a very weak wind condition in the vortex cores. Hence a minimum gap of 3 is recommended for better pedestrian level wind conditions. Besides, increasing gap from 1 to 5 reduces the shielding effect of the interfering building markedly.

Large-eddy simulations are performed to study the wake of a wall-mounted finite-length rectangular prism at a Reynolds number Re = 1.2 x 104 for the prism aspect ratio AR (= h/a) = 7 and the boundary-layer thickness ratio delta/h = 0.08, where h is the prism span and a is the frontal width of the prism cross-section. Besides, parallel experiments are conducted to provide validation for the numerical simulations. This work aims to explore the dependence of the wake dynamics on the prism cross-sectional aspect ratio CR (= b/a) that is varied from 1 to 4, where b is the side width of the prism cross-section. It has been found that the flow separating from the leading edges of the side and top faces does not reattach for CR = 1-2 but does once CR 2 but the spiral vortices on the side faces for CR 2. The formation and evolution mechanisms of these vortical structures including their interconnections and dependence on CR are discussed in detail. The conceptual models for the near-wake flow structures are also proposed with and without flow reattachment.