Journal Of Applied Fluid Mechanics
Volume:16 Issue: 6, Jun 2023

The separation efficiency and pressure drop of the dynamic separator of cement particles can be affected by many factors, like structural type, geometric parameters, and operating characteristics. In this paper, CFD modeling is applied to investigate the fluid flow behavior and the efficiency of the industrial dynamic separator with different heights of the inner cone called the vortex breaker. Simulations are based on the RSM and the DPM models. A CFD comparison of the original design and new designs has been performed. The simulation results showed that the fluid flow inside the industrial air separator is greatly dependent on the height of the vortex breaker. Interesting phenomena were observed by the numerical simulations and the results revealed that an increase in the height of the vortex breaker up to three-quarters of the magnitude of the fine powder outlet duct can improve the performances of particle separation not only by reducing 29% the cut size, and by 40% the bypassing of fine particles but also by increasing 30% the separation sharpness while keeping the pressure drop substantially unchanged.

To further improve the lift-rising effect of the attached flap on an airfoil, based on the unique movement pattern of a fluke when a dolphin moves forward, this paper puts forward a novel attached split flap model with variable curvature. The lift-type vertical axis wind turbine's typical blade airfoil NACA 0018 is taken as the research object. First, the aerodynamic performance of the two-dimensional airfoil is simulated based on the SST k-ω turbulence model. The contrast between the simulation and the experimental results proves the correctness of the numerical simulation methods in this paper. Then, the effectiveness of split flap is verified, and the lift-rising principle is briefly analyzed. Finally, the parametric study is carried out based on the flap model with variable curvature proposed in this paper, and the lift-rising principle of the variable curvature split flap is analyzed in detail. The results indicate that, with the rise of the flap's curvature index, the airfoil's lift coefficient (Cl) integrated with the flap gradually increases accordingly and tends to a constant value. The bionic research in this paper can provide a comprehensive reference for the aerodynamic shape design of airfoil trailing edge flap and the further optimization of energy efficiency of rotating machinery or aviation.

Centrally slotted box decks have been commonly used as components of bridges, especially for long-span bridges. A wind tunnel experiment was conducted to investigate the effect of attachments on the vortex-induced vibration (VIV) of the deck. In this research, the characteristics of VIV responses at different attack wind angles of 5 models considering naked bridge decks, crash barriers, wind barriers, and vehicles on bridges were studied and discussed. The effects of crash barriers, wind barriers and vehicles on the VIV behaviors of the bridge deck were also investigated experimentally. Multiple lock-in wind speed intervals were found to occur for all the models considered, and the vibrating amplitude and frequency show differences in different models. The results of the study showed that, owing to the installation of crash barriers or wind barriers, the vibrating frequency at the second lock-in interval indicated a double natural frequency. However, for the naked bridge deck model, the vibrating frequencies were close to the vertical natural frequency at all lock-in regions. Additionally, the frequency showed an evolutionary characteristic from the first lock-in interval to the second lock-in interval. Generally, the installation of crash barriers and wind barriers caused an increase of 89.8% and 123.7% on maximum vibrating amplitudes respectively. The vehicles had amplification effects on the amplitudes in both lock-in regions, with an increase of 41.5% at the maximum amplitudes. This study provides a guideline for designing bridges consisting of centrally slotted box-type decks.

The micro tube bank model is a commonly used structure in microelectro mechanical cooling systems. Flow across a micro tube bank is a basic benchmark for analyzing flow resistance and heat transfer capability. In this paper, the flow around a micro tube bank model was studied both experimentally and numerically. Micro-Particle Image Velocimetry technology was used to measure the flow field at different inlet flow rates. The laminar flow model, S-A model and standard k-ε model were used to calculate the flow field inside the micro tube bank model. By comparing the results from the three numerical models with the experimental results, there is a certain gap between them can be noted. However, it was found that the standard k-ε model is better than laminar model and S-A model in the comparison between numerical results and experimental results. In conclusion, the standard k-ε model is more suitable for the numerical calculation of the flow field around a micro scale tube bank model.

Turbocharger systems enhance the engine power and efficiency, reduce its pollution, and downsize the engine volume. As the significance of exploiting turbochargers in gasoline engines is surging among automobile manufacturers, the necessity of improvement in the system components becomes more critical. This paper investigates the impacts of a turbocharger turbine bypass and wastegate geometry alterations on the performance and the flow field characteristics via numerical simulations. The numerical method verification and mesh independence study are performed for the original geometry. The simulation results of the altered geometries indicate that better alignment between the bypassed and the bulk flows leads to higher efficiency of the turbocharging system. In addition, the bent or elbow-shaped and protruded turbine walls immediately downstream of the wheel are found to be unfavorable. It is also uncovered that if the wastegate shape and the housing walls are designed in such a way that the effects of ensuing vortices are minimized, it improves the stage efficiency, which is desirable for two-stage turbochargers. Furthermore, a novel manufacturable design is proposed in this study, which increases the efficiency and useful power by 19.9% and 6.7%, respectively.

Flow control methods have been gradually applied to improve the flow field characteristics of axial compressors. However, most of the current research is focused on the cascade, and few studies have taken a compressor as the research object. Therefore, a 3.5-stage transonic axial compressor is adopted to explore the characteristics of different flow control schemes. The effects of the micro-vortex generator (MVG), segmented boundary layer suction (BLS), and combined technology (COM) on the MVG and BLS are compared by the numerical simulation method. The research results are summarized as follows. The excessive accumulated low-energy fluid in the blade passage induces the occurrence of a corner stall in the last stage stator of an axial compressor. At this time, the compressor can still work, but the performance has accelerated deterioration. The flow characteristics are effectively improved when the MVG is introduced, the stall margin improvement ΔSM and the peak efficiency improvement Δηe of the last stage are 2.1% and 1.02%, respectively. Moreover, the BLS shows advantages in removing the three-dimensional reverse flow and decreasing the total pressure loss compared with the MVG, the ΔSM of the last stage is 2.69%, and the Δηe is 1.83%. When the combined technology is applied, it shows a significant advantage in delaying the occurrence of a corner stall, and the stall margin of the last stage is improved by 2.71%. Based on a quantitative analysis method using loss sources, the three flow control schemes show significant advantages in reducing the secondary flow loss sources and the wake loss sources. Above all, the BLS shows significant advantages in reducing the total pressure loss, and the COM shows an advantage in expanding the stable operating range. The research results will provide a reference for studies of flow control methods related to reducing flow losses and widening stability margins.

Skin friction drag can be reduced through the application of bio-inspired riblet surfaces. Numerical simulations were performed using Large Eddy Simulation (LES) to investigate the effect of using riblets on reducing skin friction drag. In this study, three different riblet configurations were used; scalloped, sawtooth and a new design, hybrid, riblet. To validate the effect of using the proposed hybrid riblet design compared with other riblets used in the literature; before applying to complex geometries, they were initially applied to a flat plate in parallel arrangement. Results showed skin friction coefficient reduction of 14% using the proposed hybrid riblet. This reduction was 9.2 times and 1.2 times more compared to sawtooth and scalloped configurations, respectively. The hybrid riblet was then applied partially and fully to NACA 0012 airfoil. Skin friction coefficient reduction of 34.5% was obtained when the hybrid riblet fully applied on the airfoil surface. Furthermore, the Convergent-Divergent (C-D) arrangement was studied, where the riblets were placed fully on the NACA 0012 and aligned with a yaw angle with respect to the flow direction. The convergent lines are inspired by the sensory part of the shark skin, whereas the divergent lines or herringbone are found on the bird feather. The two different riblet configurations, sawtooth and hybrid were modeled with the C-D arrangement and the hybrid riblet with C-D arrangement contributed to higher skin friction coefficient reduction, 34.5%, than the sawtooth riblet shape, 26.75%. Moreover, the C-D arrangement was compared to the parallel arrangement and shown that the C-D arrangement increased the lift coefficient (cl) of the airfoil, the flow separation was delayed and the overall performance of the airfoil was enhanced.

In this study, we proposed an underwater robotic swimmer integrating dual-actuated composite tentacles. We employed overlapping grid technology to manipulate virtual swimmers and performed simulations of incompressible viscous flow. To facilitate the distinction between three driving modes (the reverse, homologous, and interlace modes), the rear flexible module of the swimmer was divided into three components: thigh links, calf links, and caudal fins. The cooperative motion mechanism behind the double-tentacled module exhibited special hydrodynamic properties. Under the same kinematic parameters, the reverse mode exhibited the best energy-saving and propulsion effect, whereas the homologous mode was affected by lateral energy loss, thus resulting in the worst propulsion effect. However, the joint system exhibited anti-interference and spanwise flexibility. The interlace mode produced a certain error in the lateral displacement, and the propulsion efficiency was between the former two modes. Compared with traditional fish-like robots, the diverse actuation morphologies of the swimmer reported in this study exhibit extremely powerful self-propelled functionality, and its key features, including the geometry of an aquatic squid and the kinematics of the stretched body-caudal fin pattern, offer insights into the analysis of self-propelled hydrodynamics.

This study experimentally explores the effect of tabs with asymmetric projections on the mixing effectiveness of jets at different nozzle exit Mach numbers with subsonic ranges of 0.4, 0.6, and 0.8. The results obtained with the tab-controlled jet are compared with those of uncontrolled jets. In this experimental investigation, a pair of identical tabs is deployed along a diameter of a convergent nozzle with inlet and exit cross sections of a circle, where each tab has two triangular projections configured at locations offset to each other at a distance of 1 mm on a plain rectangular stem. The geometrical blockage due to the presence of both tabs is maintained at 5.09% to minimize the thrust loss incurred due to tabs. The counter-rotating vortices generated at different locations of the tabs, caused instability or shear distortions at the nozzle exit, promoting jet mixing and eventually leading to rapid velocity decay along the jet axis and accentuating the reduction of the potential core. Compared to plain jet, reductions in core length of about 70%, 76%, and 81% at Mach 0.4, 0.6, and 0.8, respectively, are observed with the tab-controlled jets. The total pressure decay characteristics in the radial profile along the tab and normal-to-tab orientations have shown significant distortion in the jet structure, making it asymmetrical again owing to the asymmetrical positioning of projections on the tabs. Besides, in comparison with the plain nozzle, the total pressure decay characteristics in the radial profiles of tab-controlled jets are significantly different along the axial locations in the downstream direction due to the same reason of the asymmetrical positioning of triangular projections on the tabs. The primary research goal of this experimental investigation with asymmetrical tabs is to promote jet mixing asymmetrically to achieve thrust vectoring of jets.

The objective of this paper is to obtain an excellent structure of a rotational hydrodynamic cavitation reactor (RHCR) by a numerical method and then to investigate the cavitating flow characteristics of the optimized RHCR experimentally. The RNG k-ε turbulence model combined with the Zwart cavitation model was applied to analyze the influence of the straight blade number, the baffle position and the baffle shape on the pressure field, bubble distribution and turbulence kinetic energy of the RHCR. The results show that compared to the original model, an RHCR with a straight blade number of 6, a baffle position of 0.74 and a triangular baffle offers better cavitation performance. Moreover, the energy performance and the cavitation development process of the optimized RHCR were studied experimentally. The results indicate that the multiscale bubbles are induced by straight blades and baffles of the optimized RHCR, accompanied by the twice quasi-periodic shedding dynamics in one cycle. The findings of this study have positive significance for the design and optimization of RHCRs.

This work is a numerical study on the effects of the flow structures of the power-law fluid between two concentric cylinders with an upward laminar axial flow on levels of mixing and mean residence time through the Taylor Couette system. The cylindrical annular duct presents a radius ratio of 0.5 and an aspect ratio of 8. The inner cylinder is rotating while the outer one is kept at rest. The residence time distributions (R.T.D.) method and the mean residence time (Tm) are used to determine the number of tanks in series and the dispersion coefficient to evaluate levels of mixing. To this end, a pulsed input injection of a tracer is computing at the outlet of the annulus. As a main objective of this study, is to analyze the effect of the flow structure of a power-law fluid between two concentric cylinders on the mixing level and mean residence time in a Taylor Couette system. The novelty of our work is the use of power-law fluids as particles-carrying fluids. Several parameters, such as the axial Reynolds number (Re), the Taylor number (Ta), and the power-law index behavior (n), are used to show their impact on levels of mixing. It is shown that when n increases, the number of stirred tanks in series N increases for pseudoplastic fluids (n<1), indicating low levels of mixing while the parameter (N) decreases for dilatants fluids (n>1), revealing high levels of mixing. The increase of the power-law index in the range of 0.6<n<1 decreases the dispersion coefficient, indicating the non-ideal mixing in the duct. In addition, for further increase of the power-law index in the range of n>1 increases the dispersion coefficient points to the well-mixing.

For diesel engines equipped with a combined spiral/tangential inlet, the main object of the valve structure and valve lift dissimilitude strategies is the valve, the changes of both will alter the motion state of the in-cylinder airflow, which has an important impact on the formation and combustion of the mixture. In order to investigate the flow performance of valve structure and valve lift dissimilitude, this paper used computational fluid dynamics (CFD) numerical simulation and multi-parameter regression methods to optimize the dual intake valve structure and obtained three valve structures with better intake performance first. Then, the optimized intake valve structure models were combined with the valve lift dissimilitude schemes to conduct steady-flow tests for the intake port. Through the reasonable combining of the two, the intake performance of the original engine was further improved. The results show that the valve structure has a relatively small influence on the intake mass, while it has a greater effect on the formation of the swirl in the cylinder, increasing the swirl ratio by 8.0%. The optimized valve structure model was combined with the valve lift dissimilitude scheme. It was found that the valve structure with optimal intake mass combined with the dissimilitude scheme of the largest valve lift of the spiral inlet could increase the flow coefficient by a maximum of 1.9%. The valve structure of the optimal swirl ratio combined with the dissimilitude scheme of the largest valve lift of the tangential inlet could increase the swirl ratio by a maximum of 9.7%. This study can guide diesel engines with combined intakes to increase the intake mass and improve the intake performance.

Wind energy is a renewable energy source that has grown rapidly in recent decades. This energy is converted into electricity using advanced INVELOX wind turbines. However, the wind velocity is critical, and predicting this velocity in real-time is challenging. As a result, a deep learning (DL) model has been developed to predict the velocity in advanced wind turbines using a novel enhanced Long Short-Term Memory (LSTM) model. The LSTM enhancement is executed by employing the Black Widow optimization with Mayfly optimization in the Python platform as application software. The dataset has been prepared using Ansys Fluent fluid flow analysis. In addition to that, the wind turbine power generation was computed analytically. A subsonic wind tunnel test is also performed by employing a 3-Dimensional printed physical model to validate the simulation dataset for this innovative design. The proposed MFBW-LSTM model (Enhanced LSTM with BWO and MFO) predicts efficiently, with an accuracy of 95.34%. Furthermore, the performance of the proposed model is compared to LSTM, BW-LSTM, and MF-LSTM. Accuracy, MAE, MAPE, MSE, and RMSE are among the performance criteria the proposed DL model achieves efficiently. As a result, the proposed DL model is best suited for velocity prediction of an Advanced INVELOX wind turbine in various cross sections with high accuracy.

Synthetic jet has been confirmed as a novel flow control technology. However, the existing application research on synthetic jet in axial flow compressor is still confined to cascade or low-speed axial flow compressors, and rarely high-speed axial flow compressor. The effects of three vital parameters (i.e., the action position, frequency, peak velocity) on the aerodynamic performance and stability margin are systematically studied, with a high-speed compressor rotor as the object of numerical simulation. An optimal excitation position is determined, corresponding to the core position of the compressor top blockage, as indicated by the results, which increases the stability margin and efficiency of the compressor by 13.2% and 1.15% respectively. The excitation frequency has a threshold ranging from 300Hz to 600Hz. Only when the frequency of synthetic jet exceeds this threshold can it suppress the tip leakage flow. Besides, the jet peak velocity may not have a threshold. However, the higher the peak velocity, the greater the mixing loss between the jet and the mainstream of the compressor rotor will be, thus limiting the further increase of the compressor efficiency.

The effects of inflow variations due to the working environment and flight attitude changes on turbomachines are considerable in the real world. Nevertheless, uncertainty quantification can be adopted to assess mean performance changes and perform the aerodynamic shape design as well as optimization. Thus, an uncertainty quantification method of adaptive sparse grid collocation (ASGC) was first introduced to address the inflow uncertainties’ effect issue effectively and accurately. Then, ASGC was utilized to evaluate the impacts of inlet incidence perturbations at different perturbation scales and reference inflow Mach numbers on the aerodynamic performance of a controlled diffusion cascade. The results showed that compared with the Monte Carlo simulation and static sparse gird collocation, the statistical accuracy and response accuracy of ASGC were maintained, and meanwhile its model construction efficiency was significantly improved because of the nested adaptive sampling feature. Under the perturbations of inlet incidences with high reference incidences, the mean aerodynamic loss always aggravates. The changes in aerodynamic loss nonlinearly depend on the inlet incidence perturbations, and the nonlinear dependence becomes greater when the perturbation scale. expands. At the same perturbation scale, the nonlinear dependence on the inlet incidence perturbations is further enhanced when the reference inflow Mach number rises. Finally, uncertainty quantification of the flow field revealed that the fluctuation of flow accelerations at the leading edge plays a fundamental role in determining the uncertainty of the aerodynamic loss.