Crossflow Reynolds Number Research Articles

Impact of liquid crossflow on the discharge coefficient of a gas jet hole on a flat plate

This study combines the experimental and numerical simulation methods to deeply analyze the impact of liquid crossflow on the discharge coefficient of a gas jet hole on a flat plate. Experiments were conducted to examine the influence of momentum flux ratio and theoretical momentum flux ratio on the discharge coefficient under various crossflow Reynolds numbers. It was found that the variation of the discharge coefficient with the theoretical momentum flux ratio clearly reflects the impact of the crossflow boundary layer velocity profile on the discharge coefficient. The rapid growth of velocity in the boundary layer near the wall in the direction normal to the wall surface, or the decrease in the thickness of the boundary layer, both enhance the shearing effect of the crossflow, leading to a decrease in the discharge coefficient. Analysis of the cavity morphology at the hole exit captured by high-speed camera revealed that the averaged profile of the gas–liquid boundary on the symmetrical plane of the jet below the hole can be approximated as a straight line within the scale of the hole diameter, and the sine of the angle between this line and the upper wall surface is roughly equivalent to the normalized discharge coefficient. This relationship was physically interpreted through the analysis of effective and equivalent flow cross-sectional shapes derived from numerical simulation at different crossflow Reynolds numbers and theoretical momentum flux ratios. Additionally, this paper introduces an innovative method for predicting jet flow rate based on image processing technology. A notable feature of this method is that it does not require the measurement of the pressure inside the gas chamber.

Study of the C-γ-Reθ Transition Model Based on the NNW-HyFLOW Software

Abstract Since the release of hypersonic computational fluid software NNW-HyFLOW in 2023, its computational modules have been continuously expanded for the development needs of hypersonic vehicles. The C-γ-Reθ transition model has been developed based in the framework of the NNW-HyFLOW to expand the prediction of transition in the design of high-speed vehicles. Firstly, the calibration of two basic relations of Re θc and Flength which is originally designed for the low-speed flat plate cases have been realized and expanded to high-speed flows. Secondly, the the empirical formula of Mach number correction has been adjusted by several typical high-speed transition cases. The same correction also has been made to the turbulence Prandtl number correction following the sae procedure. A crossflow transition module has been added with the calibration of the crossflow Reynolds number and validation of the experiment data of the HyTRV lifting body. The numerical tests show that the C-γ-Reθ transition model based on NNW-HyFLOW software has been basically realized with the ability of steamwise transition and crossflow transition prediction.

Investigation of the Discharge Coefficient for Laidback Fan-Shaped Holes on Turbine Blades Under Internal Crossflow Condition

Abstract The discharge coefficient of laidback fan-shaped holes on turbine blades under internal crossflow conditions is investigated using experimental and numerical simulation methods. The study is conducted on a linear cascade, with single rows of film holes set on both the pressure and suction surfaces of the test blade, coolant supplied by an internal crossflow channel. The internal crossflow Reynolds number ranged from 39,100 to 78,200, and the pressure ratio ranged from 1 to 1.5. This research considered the effects of internal crossflow Reynolds numbers and hole length-to-diameter ratio on the discharge coefficient of laidback fan-shaped holes. The findings are as follows: internal crossflow increases the inlet loss of film holes and flow separation within the holes, leading to a significant reduction in the discharge coefficient of film holes. Meanwhile, film holes on the pressure surface of the blade exhibit greater sensitivity to crossflow. Under different hole length-to-diameter ratio conditions, the length of the cylindrical section is the primary factor affecting the discharge coefficient, and the magnitude of the discharge coefficient depends on the extent of flow separation within the cylindrical section. The sensitivity of the discharge coefficient to variations in the cylindrical section length decreases once the cylindrical section length exceeds 2.8D for the pressure surface and 2.0D for the suction surface, where the inlet separation region reattaches to the wall. Under plenum conditions, there are significant differences in the discharge coefficients of film holes between the suction surface and pressure surface, especially at pressure ratios below 1.05.

Stability of fluid flow in a porous medium with uniform cross-flow and velocity slip

This work examines the evolution of small perturbations in a plane Poiseuille flow through a porous medium bounded by porous walls implemented with the Brinkman flow model. The effect of uniform cross-flow across the channel along with slip imposed on the channel walls is examined for the associated fluid flow. The modified Orr–Sommerfeld equation for the flow system under consideration is derived and then solved numerically using Chebyshev spectral collocation method. The acquired sufficient conditions ensure that fluid motion will remain stable even when the flow system is widely perturbed. The linear stability characteristics and the onset of instability is discussed for a wide range of cross-flow Reynolds number, slip length and porosity parameter. The above mentioned flow parameters have a significant stabilizing effect on the fluid flow that is depicted with neutral stability curves, growth rate dispersion curves and eigenspectrums. Asymmetric slip allows the critical Reynolds number to increase rapidly when the upper channel wall experiences more slip than the lower.

Effect of the Key Geometry and Flow Parameters on Discharge Coefficient of Laidback Fan-Shaped Hole Under Coolant Crossflow Condition

Abstract A laidback fan-shaped hole is commonly used due to its superior lateral film coverage. Its discharge coefficient is significantly influenced by internal crossflow owing to its complex geometrical structure. In this paper, the authors numerically investigate the flow mechanisms of the laidback fan-shaped hole under the influence of internal crossflow. The numerical simulations utilize the validated SST k–ω turbulence model, with the Reynolds number of internal crossflow ranging from 20,000 to 160,000 and the ratio of pressure ranging from 1 to 1.6. The results show that the different orientations of internal crossflow cause varying degrees of in-hole separation that led to a discrepancy in the discharge coefficient. The larger the Reynolds number of the crossflow is, the more drastic the change in the discharge coefficient. Furthermore, a comparison between the results obtained with and without internal crossflow has shown that the length of the cylindrical section is the primary factor determining the discharge coefficient of the laidback fan-shaped hole. The magnitude of the discharge coefficient depended on the extent of flow separation within the cylindrical section. Additionally, the numerical simulations obtained the discharge coefficient under a high internal crossflow Reynolds number of internal crossflow and a wall with a constant thickness and compared it with the predictions of a low-dimensional model of the discharge coefficient (based on our previous experimental data). The discrepancy between the results is within 10%, thus verifying the scalability of the low-dimensional model.

Design considerations for efficient spanwise-inclined air-jet vortex generators for separation control in supersonic and hypersonic flows

Shock-wave/boundary-layer interactions and associated flow separation are frequently occurring phenomena in many high-speed flow applications. Injection of spanwise-inclined air-jets is an efficient means to control shock-induced flow separation in supersonic and transonic flows. Separation-control studies in hypersonic flow are scarce and so far mostly restricted to microramp control. The objectives of the current work are to broaden the scope into hypersonic regime, investigate the influence of crossflow Mach and Reynolds number on the jet-injection flow field, and to find a suitable control parameter that is valid across a wide range of flow conditions. For this purpose, we study injection of a single spanwise-inclined jet in supersonic and hypersonic crossflows using large-eddy simulations. We analyzed the flow topology, induced vortical structures and boundary-layer statistics. The general characteristics of the jet/crossflow interactions are similar in the supersonic and hyperonic regimes: the injection of a spanwise-inclined jet induces an asymmetric flow topology with a complex system of shocks and vortical structures. We identified the ratio of injection-pressure-to-freestream-pressure as a suitable parameter to characterize and compare jet/crossflow interactions in different flow regimes. In addition, we recommend larger boundary-layer-to-jet-diameter ratio for control applications, because it delays the lift-off of major vortices. The present results suggest that rows of spanwise-inclined jets can be efficiently used to control separation also in hypersonic flow. Moreover, low momentum-flux jet injection can be potentially also used for cooling purposes.

Review[sbnd]Recent developments on applying acoustic waves for efficiency improvements of different thermofluids systems

This review classified recent works using proper acoustic waves to develop more efficient thermofluids systems for different industrial equipment such as swirl combustor, jet in crossflow, gas flare, different types of heat exchangers, cooling mechanism, aircraft wings, and turbine blades. For the swirl combustor, the range of proper excitation Strouhal number and jet pulsation intensity depends on the type of fuel, geometry of burner, swirl number, and central and annular Reynolds numbers. The combined effects of early jet break up, and centrifugal force induced by proper acoustic waves can lead to higher jet spread rate that can induce higher levels of mixing of the fuel and air in swirl combustor, improving combustion efficiency. For the transverse jet, the range of proper excitation Strouhal number and jet pulsation intensity depends on the type of fuel, geometry, and angle and direction of the burner, and jet and cross flow Reynolds numbers. Proper acoustic excitation can force the transverse jet flow to synchronized shear layer vortices. This phenomenon can cause the new vortices to appear in the upwind shear layer region of the deflected jet; then the spread, penetration, entrainment, and dispersion of the jet significantly increases, improving combustion efficiency. For the aircraft wing, vertical acoustic excitation significantly improves the lift force when the sound frequency is equal to the period of flow fluctuation in the separated boundary layer. For the heat exchanger, the ultrasonic transducer can be installed on the walls of a heat exchanger with direct contact to the fluid, improving the heat transfer coefficient. The physics of fluids behind the efficiency improvements of all mentioned cases were also clarified. Moreover, the acoustically excited impinging jets with higher cooling efficiency applied in different areas are discussed. Proper acoustic forcing can decrease the rate of unstable frequencies of disturbances related to impinging jets over a short distance. This phenomenon can significantly enhance heat transfer and improve cooling efficiency. This review paper provides insight into how acoustic waves could improve the efficiency of thermofluids systems in a variety of applications. Acoustic excitation could have the potential capability to improve the efficiency of new applications such as wind, gas or steam turbines, some types of industrial chemical mixers with parallel plane jets, aircraft wings or those of unmanned aerial vehicles, more efficient combustion chambers, and less polluting gas flares. However, the feasibility of this concept requires further investigation by the community in the future.

Improvement and application of local-variable-based transition models to complex three-dimensional configurations

The hypersonic local-correlation-based transition modeling (LCTM) and amplification factor transport (AFT) transition models are extended to crossflow-induced transitions and applied to three-dimensional hypersonic vehicles. A new crossflow Reynolds number correlation is proposed and implanted to an existing hypersonic LCTM to extend it to take account of the crossflow effect. In the hypersonic AFT model, a new transport equation is added to predict the transported crossflow amplification factor. The two improved transition models are first validated using the HIFiRE-5 configuration. The results demonstrate that both transition models predict the transition on HIFiRE-5 with reasonable accuracy. Next, the two models are applied to the X-51A forebody and the X-33 vehicle. The results show that both models are capable of predicting transition behaviors and aeroheating environments on hypersonic complex geometries. The two models also provide reasonable reflections of the effects of various factors that influence transition, including the freestream Reynolds number, turbulence level, and angle of attack.

Numerical study of turbulent flows around a cubic obstacle blown from a variable geometry jets diffuser

This research focuses on utilizing numerical simulation to analyse how modifications in the air jet diffuser shape impact the cooling efficiency of electronic parts. The main aim of this study is to understand the physical and thermal mechanisms involved in the process. The study consists in numerically predicting the physical and thermal field of a cubic-shaped obstacle placed in the centre of a square subjected to a resulting flow field created by a transverse flow and a perpendicularly oriented impacting jet. The computations were done at a Reynolds number of 3 410, analyzing three perpendicular impinging jets with the ratio of impinging and cross flow Reynolds numbers α = Rej /ReH having the values of 0.5, 1, and 1.5. The k–ω SST turbulence model was used in this investigation. The effectiveness of the methodology that was put into action was evaluated by referring to the findings derived from the experiments conducted by Masip and his team. Once the methodology was validated, we studied the effect of changing the geometric shapes of the impinging jet diffusers on the cooling efficiency. Three geometrical shapes of air diffusers were tested (circular, swirling and lobed). We noted that there is a direct correlation between flow morphology and cooling efficiency. The impact of the ratio α was analysed and found to have a significant effect on the cooling efficiency. As this ratio increases, the quantity of heat transfer increases in all three air jet diffuser cases. In relation to the lobed air jet, it was observed that the Nusselt number exhibits greater values when compared to the other air jet diffuser cases. Moreover, it was noted that the lobed air jet diffuser can enhance the heat transfer efficiency for α = 1.5 by more than 16.3 % compared to the circular air jet diffuser.

On the aero-thermal performance of flat-plate film cooling hole with variable rib heights

This study conducted a numerical investigation into the impact of different cooling air feeding methods and structural parameters of the internal ribbed crossflow channel on the performance of cylindrical film cooling holes under varying blowing ratios. The considered flow conditions encompassed two feeding methods (plenum or crossflow channel), three different rib heights (h = 2–8 mm), three internal crossflow directions relative to the mainstream (θ = 0°–180°), and four blowing ratios (M = 0.5–2.0). In the case of crossflow, the external crossflow had a Mach number of 0.3, and the internal crossflow's Reynolds number was set at 2 × 105. The study delves into flow analyses of the hole and external flow field, discharge coefficient characteristics, aerodynamic losses, and heat transfer characteristics. The findings reveal that the presence of internal crossflow significantly alters the flow field and performance compared to the coolant plenum case. However, the effects of crossflow are attenuated when internal turbulence rib structures are introduced, and this damping effect is further pronounced as the rib height increases. The aerodynamic and cooling characteristics of the hole progressively approach those of a plenum supply form, a phenomenon aptly termed the “Plenum effect” of the ribbed crossflow channel.

Effect of crossflow oscillation Strouhal number on circular cylinder wake

The wake flow features and aerodynamic characteristics of a circular cylinder in an oscillating crossflow were experimentally investigated. The study focused on crossflow oscillation Strouhal numbers that were smaller than the natural wake vortex-shedding Strouhal numbers. Crossflow oscillations were generated using a downstream rotating plate method. The flow evolution processes were observed using laser-light sheet assisted smoke flow visualization technique. Wake instability and time-averaged velocities were assessed using a one-component hot-wire anemometer and particle image velocimetry. Pressure distributions on the cylinder's surface were quantified using a linear pressure scanner, obtaining pressure coefficient distributions and drag forces. The wake instability Strouhal number, velocity vectors, streamline patterns, and recirculation bubble geometries in the wake region of the circular cylinder were determined. The wake turbulence properties were analyzed using the triple-decomposition method, including turbulence intensities and Lagrangian integral length and time scales. The results of natural and oscillating crossflows were compared. The wake vortex-shedding Strouhal number was lower than the natural Strouhal number but higher than the crossflow oscillation Strouhal number. It was primarily influenced by the oscillation Strouhal number and the Reynolds number of the crossflow. Critical crossflow Reynolds and oscillation Strouhal numbers were identified, beyond which the wake vortex-shedding Strouhal number reached a constant value. The crossflow oscillation intensity did not significantly affect the wake vortex-shedding behavior. The study provided quantitative descriptions and discussions of recirculation bubble geometries and statistical turbulence properties. Furthermore, the crossflow oscillations led to a substantial reduction in the drag coefficient experienced by the circular cylinder.

Numerical analysis of hydromagnetic particulate Reiner-Rivlin fluid flow in an asymmetric non-uniform channel with a heat source

The main objective of the present article is to investigate the hydromagnetic particle Reiner-Rivlin fluid flow in an asymmetric (divergent) channel. The non-dimensionalized equations solved by the shooting method. The graphs are intended to examine how different developing parameters affect the thermal and velocity fields. The effects of various parameters on skin friction and the rate of heat transmission along channel walls are investigated using tabular data. The current results are in admirable agreement with the published data. The fluid velocity delineates in the first portion of the channel and rockets up in the second when the inelastic parameter increases. An increase in cross-flow Reynolds number is accompanied by an increasing tendency in particle temperature. Several areas, like metal steam resistors, fiber suspension in paper manufacture, etc., are significantly impacted by the magnetic field’s action on Reiner-Rivlin fluid through asymmetric channels.

Influence of Dimple Diameter and Depth on Heat Transfer of Impingement-Cooled Turbine Leading Edge with Cross-Flow and Dimple

Today, impingement cooling structures with dimples can effectively ease the burden of turbine blades. This paper investigates the effect of dimple diameter and depth on the heat transfer of the target surface on a laminar-cooled turbine blade with a cross-flow and dimple numerically to find the mechanism behind it so that the dimple can be better used in turbine cooling. The commercial software ANSYS 19.2 and a baseline (BSL) turbulence model is used during the numerical computation. In this paper, the cross-flow Reynolds number varies from 15,000 to 60,000, while the jet Reynolds number remains at 30,000. When the cross-flow Reynolds number changes, due to the location change in vortexes generated inside or around the dimple, the two dimple parameters affect heat transfer differently. When the cross-flow Reynolds number is lower than the jet Reynolds number, dimples with smaller diameters and depths lead to better heat transfer performance. When the cross-flow Reynolds number exceeds the jet Reynolds number, dimples with bigger diameters and depths result in better heat exchange performance. The results also indicate that, while the dimple diameters remain constant, the rise of the cross-flow Reynolds number enhances the heat transfer of the dimple structure.

Large eddy simulation of film cooling flow from diffusion slot hole with crossflow coolant configuration

A three-dimensional compressible large eddy simulation (LES) method was performed to explore the flow and heat transfer characteristics in the hole and mixing zone of a crossflow film cooling model. A traditional cylindrical hole and diffusion slot hole were selected as the cases for the film hole. The characteristics of the crossflow film flow-field and the influence of the internal crossflow on the film cooling of the diffusion slot hole were explained by the vortex flow in the hole and the instantaneous/time-averaged jet mixing. The results showed that helical motion is easily induced in the holes under the influence of crossflow. Asymmetric outlet flow behavior is the main reason for the asymmetric characteristics downstream of the hole. The difference in the blowing ratio results in the difference in the strength of the spiral vortex and the central vortex tube inside the hole. For the diffusion slot hole, the high-speed zone caused by the crossflow effect at the hole-inlet gradually evolves into strip shapes under the combined action of axial extrusion and spanwise diffusion. With the disappearance of the helical structure, the high-speed areas gradually converge on both sides of the hole exit in the span direction, and the streamline at the exit develops relatively smoothly. The inlet crossflow and the crossflow Reynolds number have little effect on the film cooling effectiveness of the diffusion slot hole. With an increase in the blowing ratio, the lateral diffusion capacity of the film is gradually enhanced. Furthermore, compared with the cylindrical hole, the instantaneous film fluctuation region of the diffusion slot hole case is smaller in range and more symmetrical in distribution. These findings advance the understanding of the film cooling of diffusion slot holes.

Mixing in Low Reynolds Number Reacting Impinging Jets in Crossflow

AbstractPrevious efforts to model uranyl fluoride formation in an impinging jet gas reactor underpredicted spatial mixing and overpredicted chemical conversion into particulates. The previous fluid dynamics model was based on the solution of the Reynolds Averaged Navier Stokes equations. After simulating fluid dynamics, aerosol dynamics were superimposed onto CFD-simulated gas reactant species concentrations. The current work explores the influence of complex unsteady flow features on the overall flow physics and chemistry for a low Reynolds number, opposed flow, impinging jet gas reactor where there is a low Reynolds number cross flow. The objective of this study was to assess the impact of model formulation on scalar mixing and transport. Transient flow simulations were performed using Scale Resolving Simulations. Large-Eddy Simulations with the dynamic Smagorinsky turbulence model were performed along with simulations which directly resolved the flow. Average and root-mean-square (RMS) velocities and species concentrations were computed along with modeled and resolved turbulence kinetic energy (TKE), modeled turbulence dissipation, and modeled turbulent viscosity. Lagrangian flow tracers were also used to quantify species concentrations along path lines emanating from the jet tips. Transient simulation data were compared to results from RANS simulations using the k-ω shear stress transport (SST) model and Reynolds Stress Model (RSM). Transient simulations showed spatial mixing patterns which were more consistent with experimental data and helped elucidate the process of particle formation observed in experiments.

The role of jet-to-crossflow velocity ratio on convective heat transfer enhancement in the cooling of discrete heating modules

• This study aims to evaluate the effects of the momentum contribution of the jet flow on heat transfer and thermohydraulic performance in the cooling of blocks simulating electronic components with crossflow and jet flow. • The jet nozzle used in addition to the cross flow increases not only the thermal enhancement factor of the first block, but also the thermal enhancement factor of all blocks. • The contribution of the jet to the improvement in heat transfer is greater than the increase in pressure drop. Thus, the jet impingement cooling appears to be a good alternative for electronics cooling. This study aims to investigate the role of jet-to-cross flow velocity ratio on convective heat transfer and flow characteristics in a channel with discrete heating modules simulating electronic components. Three-dimensional numerical simulations are performed using the finite volume method. The findings obtained for different velocity ratios of the jet-to-crossflow are compared with the reference case (crossflow solely). While keeping the crossflow velocity and the crossflow Reynolds number ( Re c = 5000 ) constant, numerical calculations are performed for six different velocity ratios ( U r = 1.0 , 2.0 , 4.0 , 6.0 , 8.0 and 10.0 ). The focus is on the role of the velocity ratio ( U r ) on the mean Nusselt number ( Nu m ) on the modules’ surfaces, the Nusselt number ratio ( Nu r ), the friction coefficient ratio ( f r ) obtained throughout the channel and the thermal enhancement factor ( TEF ). As a result of the study, it is revealed that the momentum of jet flow becomes dominant over crossflow, the influence of jet flow on convective heat transfer increases, and the thermal enhancement factor increases depending on the increasing jet-to-cross flow velocity ratio.

Experimental and numerical research on film cooling characteristics on the compound angle hole

Experimental research was conducted for studying the effect of blowing ratio (M) as well as cross-flow Reynolds number (Rec) on distribution characteristics in film cooling effectiveness (η) and heat transfer coefficient (h) on compound angle hole configuration with applying transient liquid crystal technology. At the same time, the distribution characteristics of discharge coefficient (Cd) were measured by the flow resistance experiment. Furthermore, the net heat flux reduction (NHFR) is applied for assessing the film cooling performance. Numerical simulation was carried out to present the flow features for analyzing the film cooling mechanism. Results demonstrate that the increasing Rec presents a great influence on the measured Cd at the small M. The flow loss caused by the cross-flow presents the slight influence on the measured Cd at the large M. In addition, the measured Cd shows upward tendency with the increase in M and is almost no change until M increases to a certain extent. At small M, the measured η at the hole downstream area is higher and descends with the increase in Rec. At the large M, jets at the hole outlet almost separated from the surface. Thus, the measured η at the hole downstream area is lower and rises with the increase in Rec. The increase in M makes the measured h at the hole downstream area descend. The increase in Rec makes the measured h of the hole downstream area rise. The NHFR shows the decreasing tendency with the increasing M. Under the condition of M = 0.5, values of the laterally averaged NHFR are between 0 and 0.4, which represents the positive effect on film cooling function. At the condition of M = 2.0, values of laterally averaged NHFR are less than 0, involving negative effects. Under the condition of M = 1.0, most of the laterally averaged NHFR presents the positive values, and only a small part of the laterally averaged NHFR is the negative values. Due to the rising η and the descending h, the NHFR decreases in the increase in Rec under the condition of M = 0.5 and M = 2.0. The increase in Rec presents the slight influence on the NHFR under the condition of M = 1.0.

Entropy Generation on Pulsatile Hydromagnetic Flow of Jeffrey Nanofluid in a Porous Channel with Brownian Motion, Thermophoresis, and Heat Source/Sink Using Cattaneo-Christov Heat Flux

In this work, the entropy generation on MHD pulsatile flow of Jeffrey nanofluid in a porous channel with Cattaneo-Christov theory is investigated. Buongiorno nanofluid model is utilized to see the impact of thermophoresis and Brownian motion. The consequences of thermal radiation, heat source/sink, viscous dissipation, and Ohmic heating are considered. The governing equations are transformed to a system of ordinary differential equations by applying the perturbation procedure then numerically tackled with fourth-order Runge-Kutta scheme aided by shooting technique. The influences of different emerging parameters and variables on velocity, temperature, nanoparticles concentration, entropy generation, and Bejan number are presented graphically. The influence of emerging parameters on heat and mass transfer rates are prearranged in table. The temperature of nanofluid increases with an enhancement in Eckert number, thermophoretic, and Brownian movements, whereas it decelerates for the rising values of cross flow Reynolds number. The concentration of nanoparticles diminishes with an increment in the Lewis number, chemical reaction parameter, and Brownian motion parameter whereas it improves with a rise in thermophoresis parameter. The entropy generation is an increasing function of Eckert number and radiation parameter. Further, the Bejan number is enhanced for increasing the values of Hartmann number.

Film cooling characteristics of trench film hole fed by the internal cross-flow

The paper describes the film cooling characteristics of the trench film hole fed by the internal cross-flow. Three internal cross-flow cases are investigated by using numerical simulations. Results show that the main flow structures of the smooth and 45° rib cases feature helical and asymmetrical, and that of the 135° rib case is straight and symmetrical. When M = 0.5, the film cooling effectiveness η of the 135° rib case is the highest at two cross-flow Reynolds numbers. As [Formula: see text] increases to 1.0, the η of the 135° rib case at Rec = 100,000 is the highest. When [Formula: see text] = 2.0, interestingly, the highest η is achieved by the 45° rib case at Rec = 100,000. The discharge coefficient and total pressure loss coefficient increase with M for the three cases. The discharge coefficient of the 135° rib case is the highest, whereas that of the 45° rib case is the lowest. And the discharge coefficient at Rec = 100,000 is lower than that at Rec = 50,000 because the blockage is more serious at Rec = 100,000, while the total pressure loss coefficient at Rec = 100,000 is higher than that at Rec = 50,000. When Rec = 50,000, the 135° rib case exhibits a higher heat transfer coefficient HTC than the smooth case, while the area-averaged HTC of the 45° rib case depends on the M. When Rec = 100,000, the area-averaged HTC of the 45° rib case is always highest while that of the 135° rib case is always lowest. In addition, the net heat flux reduction ( NHFR) is mainly affected by the η and is more sensitive to the cross-flow at high Rec and low M.

The interactions of a circular synthetic jet with a turbulent crossflow

The three-dimensional flow of a circular synthetic jet interacting with a turbulent crossflow is investigated with unsteady Reynold-Averaged Navier–Stokes simulations. The effects of jet momentum are examined using three blowing ratios (CB=0.32, 0.67, and 1.10) at constant actuation frequency (f=300 Hz), approach crossflow Reynolds number, Reθ=900, and boundary layer thickness, δ/d=7.25, where d is the jet diameter. The results showed that the expelled jet is accompanied by a reverse flow region on the downstream side which undergoes alternating expansion and contraction during the jet cycle. The size of the reverse flow region and depth of penetration increased with increasing jet momentum. For the low momentum jet, the expelled flow structure evolved into a hairpin vortex which significantly enhanced the wall shear stress in the spanwise direction and near the jet exit. The higher momentum jets, on the other hand, exhibited strong vortex loops around the expelled jet column that transitioned into trailing vortex pairs and a tilted vortex ring further downstream. Along the wall, both horseshoe vortex upstream of the jet exit and tertiary vortices downstream were found attached to the wall. The strong tertiary vortices promoted downwash of fluids which significantly enhanced the wall shear stress along the symmetry plane for the medium and high momentum jets. The impact of the tertiary vortices increased with the jet momentum, offering greater potential for flow separation control.