Jet Inclination Angle Research Articles

EFFECT OF SECONDARY JET INCLINATION ANGLE ON HEAT TRANSFER IN A CONFINED IMPINGING JET ARRAY

In this study, the heat transfer effects on the impingement surface in confined impinging array jet flows with inclined secondary jets were experimentally investigated. Temperature distributions were obtained with a thermal camera throughout the center axis of the target plate for Reynolds number values of 20,000 and 30,000, inter-plate aperture values of 0.5, 1, 3, and 6, and secondary jet inclination angles of 45°, 52.5°, and 60°. From the temperature distributions obtained, the influence of Reynolds number, inter-plate aperture, and inclination angle of secondary jets on the Nusselt distributions on the target plate was investigated. It was perceived that the Nusselt values on the target plate increase with increasing Reynolds number and decrease with increasing inter-plate aperture. The location of the top points of the Nusselt number distribution is shaped on the target plate in line with the axes of the secondary jets. These distributions shift to larger ± r/D values as the aperture between the plates increases. As the inclination angle of the secondary jets increases, the positions of the secondary jets on the target plate approach the primary stagnation zone, and the top points at these positions become stronger. The most homogeneous Nusselt number distribution occurs when the secondary jet inclination angle is 60° and the aperture H/D = 1.

The Subparsec-scale Structure and Evolution of Centaurus A. III. A Multi-epoch Spectral and Polarimetric VLBA Study

Abstract The Centaurus A radio galaxy, due to its proximity, presents itself as one of the few systems that allow the study of relativistic jet outflows at subparsec distances from the central supermassive black holes, with high signal to noise. We present the results from the first multi-epoch spectropolarimetric observations of Centaurus A at milliarcsecond resolution, with a continuous frequency coverage of 4.59−7.78 GHz. Using a Bayesian framework, we perform a comprehensive study of the jet kinematics, and discuss aspects of the jet geometry, including the jet inclination angle, jet opening angle, and the jet expansion profile. We calculate an upper limit on the jet’s inclination to the line of sight to be <25°, implying the lower limit on the intrinsic jet speed to be 0.2c. On the observed very long baseline array scales, we detect new jet components launched by the central engine since our previous study. Using the observed frequency-dependent core shift in Centaurus A, we find the jet to have reached constant bulk speed and conical outflow at the regions probed by the base of the jet at 7.78−4.59 GHz, and we also estimate the location of the central black hole further upstream. Through polarimetric analysis (by applying rotation measure synthesis for the first time on very long baseline interferometry data), we find evidence to suggest the possible onset of acceleration toward the leading edge of Centaurus A’s subparsec-scale jet studied here.

Wind Turbine Enhancement via Active Flow Control Implementation

The present research enhances the efficiency of an airfoil section from the DTU-10MW Horizontal Axis Wind Turbine (HAWT) via Active Flow Control (AFC) implementation and when using synthetic jets (SJ). The flow around two airfoil sections cut along the wind turbine blade and for a wind speed of 10 m/s is initially simulated using the CFD-2D-RANS-Kω-SST turbulence model, from where the time-averaged boundary layer separation point and the associated vortex shedding frequency are obtained. On a second stage of the paper, and considering one of the two airfoil sections, the boundary layer separation point previously determined is used to locate the SJ groove as well as the groove width; the three remaining AFC parameters, momentum coefficient, jet inclination angle, and jet pulsating frequency, are parametrically optimized. Thanks to the energy assessment presented in the final part of the paper, the study shows that a considerable power increase of the airfoil section can be obtained when attaching the former separated boundary layer. The extension of the optimization process to the rest of the blade sections where the boundary layer is separated would lead to an efficiency increase of the HAWT. The Reynolds numbers associated to the respective airfoil sections analyzed in the present manuscript are Re = 14.088×106 and Re = 14.877×106, the characteristic length being the corresponding chord length for each airfoil.

Flow behavior and heat transfer characteristics of liquid film on vertical hot surface by inclined jet impingement

In this study, the flow behavior and heat transfer characteristics of the liquid film on the hot wall by inclined jet impingement are experimentally studied in detail. The effects of jet parameters, such as jet inclination angle, impingement distance, jet Reynolds number (Rej), and nozzle diameter are explored. The liquid film flow is visualized using a high-speed camera, and the surface temperature and heat flux are obtained by solving the inverse heat conduction problem. The results indicate that the liquid film shape is strongly affected by jet inclination angle but is almost unaffected by other parameters. As the inclination angle increases, the liquid film shape changes from elliptical to fusiform. In addition, the onset, enhancement, and disappearance of boiling cause the expansion and contraction of liquid film. The splashing rate is barely affected by jet parameters and remains within the range of 80–95 % under all conditions. The propagation of wetting fronts exhibits anisotropy. Except for the impingement distance, the position of wetting fronts along y-axis direction displays a high dependence on all parameters. The Rej and nozzle diameter have a significant effect on the heat flux at the impingement point and parallel flow zone, while the jet inclination angle and impingement distance only effect the impingement point. The visualization image proves that the droplet impingement pattern is the main reason for the increase in heat flux at higher impingement distances. Optimizing jet parameters can promote the wall to enter the rapid cooling stage in advance and increase maximum heat flux, thereby improving the maximum cooling capacity of the jet. Finally, an empirical equation is proposed to predict the maximum Nusselt number.

Constraining the physical properties of large-scale jets from black hole X-ray binaries and their impact on the local environment with blast-wave dynamical models

ABSTRACT Relativistic discrete ejecta launched by black hole X-ray binaries (BH XRBs) can be observed to propagate up to parsec-scales from the central object. Observing the final deceleration phase of these jets is crucial to estimate their physical parameters and to reconstruct their full trajectory, with implications for the jet powering mechanism, composition, and formation. In this paper, we present the results of the modelling of the motion of the ejecta from three BH XRBs: MAXI J1820$+$070, MAXI J1535–571, and XTE J1752–223, for which high-resolution radio and X-ray observations of jets propagating up to $\sim$15 arcsec ($\sim$0.6 pc at 3 kpc) from the core have been published in the recent years. For each jet, we modelled its entire motion with a dynamical blast-wave model, inferring robust values for the jet Lorentz factor, inclination angle and ejection time. Under several assumptions associated to the ejection duration, the jet opening angle and the available accretion power, we are able to derive stringent constraints on the maximum jet kinetic energy for each source (between $10^{43}$ and $10^{44}$ erg, including also H1743–322), as well as placing interesting upper limits on the density of the ISM through which the jets are propagating (from $n_{\rm ISM} \lesssim 0.4$ cm$^{-3}$ down to $n_{\rm ISM} \lesssim 10^{-4}$ cm$^{-3}$). Overall, our results highlight the potential of applying models derived from gamma-ray bursts to the physics of jets from BH XRBs and support the emerging picture of these sources as preferentially embedded in low-density environments.

DNS on flame and flow characteristics of a H2-O2-H2O lifted flame with inclining impinging jets geometry

Hydrogen-fueled gas turbines play one of the key roles in future carbon-neutral energy structure. Due to hydrogen’s high flame speed and extreme flame temperature, design of burners applying hydrogen as fuel is of challenge. In this work, we conduct direct numerical simulations to investigate a non-premixed steam-diluted oxygen/hydrogen combustion, which is formed by inclined impinging fuel and oxidizer jets injected by sub-millimeter nozzles. This configuration inherently prevent flashback and has a higher mixing efficiency enhanced by jet impingement, thereby leveraging advantages of both conventional premixed and non-premixed configurations. The flame is lifted flame held at the jet impinging position far away from the wall boundary. The most intensive mixing process occurs at the outer sides of the two branches of hydrogen jet after impinging, forming the flame base and resulting in an edge-flame configuration. A larger jet inclination angle leads to more effective bulk turbulence mixing because of the increased mixing volume, thereby enhancing combustion completeness. Simultaneously, it results in lower wall heat flux due to gentler upstream recirculation of burnt products. Chemical explosive mode analysis is conducted to analyze the combustion procedure from ignition to burnt out. The flame is held by the recirculation of high-temperature burnt products upstream of the impingement position, and its structure is primarily formed by the simultaneous ignition of a widespread explosive mixture enhanced by intense turbulence.

The 2018 Outburst of MAXI J1820+070 as Seen by Insight-HXMT

We present an analysis of the whole 2018 outburst of the black hole X-ray binary MAXI J1820+070 with Insight-HXMT data. We focus our study on the temporal evolution of the parameters of the source. We employ two different models to fit the disk’s thermal spectrum: the Newtonian model diskbb and the relativistic model nkbb. These two models provide different pictures of the source in the soft state. With diskbb, we find that the inner edge of the disk is close to the innermost stable circular orbit of a fast-rotating black hole and the corona changes geometry from the hard to the soft state. With nkbb, we find that the disk is truncated in the soft state and that the coronal geometry does not change significantly during the whole outburst. However, the model with nkbb can predict an untruncated disk around a fast-rotating black hole if we assume that the disk inclination angle is around 30° (instead of ∼60°, which is the inclination angle of the jet and is usually adopted as the disk inclination angle in the literature) and we employ a high-density reflection model. In such a case, we measure a high value of the black hole spin parameter with observations in the soft state, in agreement with the high spin value found from the analysis of the reflection features and in disagreement with the low spin value found by previous continuum-fitting method measurements with the disk inclination angle set to the value of the jet inclination angle.

Study on heat transfer and pressure steady-state characteristics of a floating nozzle under a moving wall

This work considers the flow field as two-dimensional turbulent flow and studies the steady-state properties of heat transfer and the pressure of the suspension nozzle. An adiabatic wall parallel to the moving wall and two slit entrances at either end of the adiabatic wall make up the rectangular flow field. The SST k-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k - \\omega$$\\end{document} turbulence model is used in the turbulence computation. Both qualitative and quantitative analyses are conducted on the distribution of the flow field, temperature field, local Nusselt number, local pressure coefficient, average Nusselt number, and average pressure coefficient under various combination conditions. The findings indicate that when the suspension nozzle's flow field varies greatly, wall-jet velocity ratio is 0.1. A rise in Jet inclination angle is not helpful for the wall's suspension, and it has minimal effect on the flow field. The flow field is greatly influenced by separation space-slit width ratio. Larger separation space-slit width ratio values are advantageous for the wall's heat transmission but unfavorable for the wall's suspension. The flow field is most influenced by wall-jet velocity ratio. The wall's ability to convey heat is stronger the higher the wall-jet velocity ratio, but its ability to support weight falls.

A Multiwavelength Study of the Hard and Soft States of MAXI J1820+070 During Its 2018 Outburst

We present a comprehensive multiwavelength spectral analysis of the black hole (BH) X-ray binary MAXI J1820+070 during its 2018 outburst, utilizing AstroSat far-UV, soft X-ray, and hard X-ray data, along with (quasi-)simultaneous optical and X-ray data from the Las Cumbres Observatory and NICER, respectively. In the soft state, we detect soft X-ray and UV/optical excess components over and above the intrinsic accretion disk emission (kT in ∼ 0.58 keV) and a steep X-ray power-law component. The soft X-ray excess is consistent with a high-temperature blackbody (kT ∼ 0.79 keV), while the UV/optical excess is described by UV emission lines and two low-temperature blackbody components (kT ∼ 3.87 and ∼0.75 eV). Employing continuum spectral fitting, we determine the BH spin parameter (a = 0.77 ± 0.21), using the jet inclination angle of 64° ± 5° and a mass spanning 5–10 M ☉. In the hard state (HS), we observe a significantly enhanced optical/UV excess component, indicating a stronger reprocessed emission in the outer disk. Broadband X-ray spectroscopy in the HS reveals a two-component corona, each associated with its reflection component, in addition to the disk emission (kT in ∼ 0.19 keV). The softer coronal component dominates the bolometric X-ray luminosity and produces broader relativistic reflection features, while the harder component gets reflected far from the inner disk, yielding narrow reflection features. Furthermore, our analysis in the HS suggests a substantial truncation of the inner disk (≳51 gravitational radii) and a high disk density (∼1020 cm−3).

Effect of hot air inclined jet impingement to container for controlling of energy storage of PCM: experimental and numerical investigation

Purpose This study aims to focus on understanding how different jet angles and Reynolds numbers influence the phase change materials’ (PCMs) melting process and their capacity to store energy. This approach is intended to offer novel insights into enhancing thermal energy storage systems, particularly for applications where heat transfer efficiency and energy storage are critical. Design/methodology/approach The research involved an experimental and numerical analysis of PCM with a melting temperature range of 22 °C–26°C under various conditions. Three different jet angles (45°, 90° and 135°) and two container angles (45° and 90°) were tested. Additionally, two different Reynolds numbers (2,235 and 4,470) were used to explore the effects of jet outlet velocities on PCM melting behaviour. The study used a circular container and analysed the melting process using the hot air inclined jet impingement (HAIJI) method. Findings The obtained results showed that the average temperature for the last time step at Ф = 90° and Re = 4,470 is 6.26% higher for Ф = 135° and 14.23% higher for Ф = 90° compared with the 45° jet angle. It is also observed that the jet angle, especially for Ф = 90°, is a much more important factor in energy storage than the Reynolds number. In other words, the jet angle can be used as a passive control parameter for energy storage. Originality/value This study offers a novel perspective on the effective storage of waste heat transferred with air, such as exhaust gases. It provides valuable insights into the role of jet inclination angles and Reynolds numbers in optimizing the melting and energy storage performance of PCMs, which can be crucial for enhancing the efficiency of thermal energy storage systems.

Effects of cavitation and hydraulic flip on liquid film formed by jet impinging on the wall

The technology of the liquid film formed by jet impinging on the wall is widely applied in the aerospace, steel quenching, and cleaning. In this paper, the spreading and evolution of the liquid film are experimentally studied. The effects of the cavitation and hydraulic flip on the film are examined, and it is identified that they are a serious problem of the nozzle design. Results demonstrate that the jets formed by using a nozzle with 120° contraction angle and 3.5 mm outlet length sequentially produce the cavitation and hydraulic flip as the Reynolds number increases. Small contraction angle or long outlet length promotes the stability of the discharge coefficient and jet states and inhibits the occurrence of the cavitation and hydraulic flip. For the flip jet, the jet cross section is axially switched. Several patterns of the liquid film, such as the gravity flow, gravity flow with dry patch formation, rivulet flow with outward streams, and outward flow with triple rivulets, etc., are observed as the jet regime and inclination angle change. Particularly, for the film formed by the cavitation jet, the rivulets and dry patches emerge in the tail of the film; meanwhile, a lot of splashing droplets are generated. For the film generated by the flip jet, the bifurcation of the film shapes occurs. An impressive flow feature is that the two sprays are formed when the flip jet impinges on the wall, which is caused by the collision of the fluids in the secondary impingement zones.

Influence of inclined unconfined circular air jet impingement on local heat transfer characteristics of smooth flat plate

The influence of inclined unconfined circular air jet impingement on local heat transfer characteristics of smooth flat plate is studied experimentally. The experimental investigation was conducted with jet inclination angles of 45°, 60° and 75°, jet Reynolds number of 12000–28000 and nozzle to target surface distance of 1–6. The Nu characteristics is studied in different radial direction angles on flat plate ranging from θ = 0° to 180° in stagnation and wall jet area for different z/d, Re and jet inclination configurations. The Nu characteristics are obtained by using an IR thermal imaging and thin foil approach. The Nu characteristics of different jet inclination angles (φ = 75°, 60° and 45°) was compared with vertical jet (φ = 90°) for different z/d and Re. Asymmetric in Nu characteristics increases with decrease in jet inclination about the geometric impingement point. With jet inclination, the maximum Nu value shifts away from geometric impinging point towards the uphill area of target plate. The displacement of maximum Nu from geometric impinging point towards the uphill area is highly pronounced at lower z/d and higher Re for a given jet inclination configuration. The isothermal Nu ring is reported at r/d ∼2 from geometric point in wall jet area. Within isothermal ring, Nu increases with radial direction angles from 0° to 180° and reverse behavior is observed outside the isothermal Nu ring. Correlations of Nu are obtained at geometric point and maximum Nu point with maximum deviation of ±10 %. Moreover, correlation for average Nu is also presented with and accuracy of ±3.4 %.

Experimental study on air impinging jet for effective cooling of multiple protruding heat sources

Air Impinging Jet is an effective cooling method for various applications, ensuring optimal performance and reliability of heat-generation systems. In the present work, a novel technique of cooling discrete protruding heat sources mounted in a rectangular channel by using a double air jet is introduced experimentally. A constant and uniform heat flux is produced from protruding heat source surfaces where the bottom and the upper channel walls are insulated. The effects of various parameters on the heat source cooling performance such as the Nusselt number for single and double air jets are obtained. Various parameters such as the air Reynolds number, aspect ratio, double jet position ratio, and jet inclination angle are investigated. The results show that those parameters effectively affect the average temperatures and the standard deviation of all protruding heat sources. It is indicated that the maximum value of the average Nu number occurs at the heat source just underneath the impinging air jet compared to other downstream heat sources. The highest average Nu is achieved at a position ratio of 3/7 and an inclination angle of 10o. The cooling system accomplishes an acceptable Nu and temperature uniform distribution for a position ratio of 4/7 compared to the other position ratios. The improved performance and longevity of heat sources are achieved by the innovative double-air jet method, which archives a consistent temperature distribution for all projecting heat sources.

Cooling performance of droplet-shaped Kagome truss structure combined with jet array impingement composite cooling structure

Gas turbine is one of the most efficiency conversion equipment of heat into power, which is widely used in aviation propulsion and power generation. With the gas inlet temperature of gas turbine skyrocketing recently, gas turbine can achieve higher efficiency but the super high temperature far exceeds the bearable temperature limits of blade material. This causes a great threaten in lifespan of turbine blades and making advanced and efficient cooling structures for blades essential. To enhance the cooling effectiveness of middle chord region of gas turbine blade, a novel droplet-shaped Kagome truss structure (DKTS) is proposed and investigated through experimental and numerical analysis. Subsequently, within jet impingement channel, DKTS is compared against circular pin-fins (CPF), droplet-shaped pin-fins (DPF), and circular Kagome truss structures (CKTS) for fluid flow and heat transfer performance. The experimental method is used to study effects on cooling characteristics between DKTS and CKTS under different operating conditions. The numerical method is used to study effects on cooling characteristics among CPF, DPF, CKTS and DKTS, and to study influences of investigated parameters on cooling performance of DKTS. Experimental results show that under equivalent windward areas, both heat transfer efficiency and flow performance of DKTS are better than those of CKTS. The results of numerical simulations indicate that at the same porosity across jet Reynolds numbers ranging 5000–50000, DKTS increases thermal-hydraulic performance by 11.1%–17.5% relative to CKTS. Moreover, DPF and DKTS reduce flow resistance and augment heat transfer capabilities as compared to CPF and CKTS. This shows that turbulators with droplet-shaped rods have better thermal-hydraulic performance. Finally, the effects of differing jet Reynolds numbers, diameter, tail angles, and inclination angles on fluid flow and heat transfer characteristics of DKTS are conducted. These results may provide a reference for further optimization researches or industrial applications of DKTS.

An experimental study and analysis of lift-off length in inclined nonpremixed turbulent jet flames

The lifted flame behavior of inclined turbulent jets, considering the relative angle between the fuel jet momentum and flame buoyancy was investigated experimentally by varying the inclination angle of nonpremixed fuel jets. Variations of lift-off length from the flame base to the nozzle exit was quantified experimentally with nozzles of various diameters (2, 3, and 5 mm) and inclination angles (range of −90° to 90°). The data was analyzed based on the experimental finding of upstream preheating effect depending on inclination angles. Major findings are as follows: (1) The lift-off length (h) increases linearly with the increase in initial fuel jet velocity (ue) at a fixed inclination angle. The proportionality slope κ of the linear relationship between h versus ue decreases appreciably with jet inclination angle for the negatively inclined flames; while for the positively inclined flames, the lift-off length decreases relatively weakly. (2) Physical analysis on the flow characteristics of inclined jets was conducted, and the preheating effect was proposed based on the combustion behaviors, especially for the negatively inclined jet flames. The preheating temperatures of unburned fuel/air mixtures at the flame base and nozzle exit were experimentally quantified, revealing that the negatively inclination angle can have a significant influence on the preheating temperatures. (3) Based on the proposed preheating mechanism, a physical model accounting for the effect of jet inclination angle was developed to quantify the lift-off length of inclined jet flames. The proposed model successfully represented lift-off lengths at all the experimental conditions with various inclination angles and nozzle diameters. The present findings provide new data set and a reasonable physical model for lifted flame behavior of inclined turbulent jet flames, revealing the effect of the relative angle between fuel jet momentum and flame buoyancy.

Effect of single and multiple protrusions on thermal performance of slot jet impingement with curved surface

The current study uses numerical methods to evaluate the thermal and flow characteristics of air jet impinging on concave surfaces with single and multiple protrusions on a surface. The impact of different operating parameters is also studied, including Reynolds number, jet inclination angle and nozzle-to-plate distance (H/B). No significant improvement in the overall thermal performance is noted with a single protrusion on the surface, although a higher heat transfer is observed in the stagnation zone. On the other side, the multiple protrusions on the surface have shown an increase or decrease in the overall thermal performance of jet impingement depending on protrusion diameter and height. The maximum improvement in the overall Nu is noted up to 19 % for the multi-protruded surface at H/B = 6 with orthogonal jet impingement. An oblique jet decreased the overall thermal performance compared to the orthogonal jet, regardless of the jet inclination angle.

Air curtain in informal shopping malls: Optimization of the air curtain operating parameters for heat and smoke confinement

The operating parameters of commercially available air curtains, due to their promise in the confinement of fire-generated heat and smoke, have been systematically examined. Operating parameters such as the jet velocity, jet inclination angle, jet width, flow rate, and the number of air curtain jets are explored for the maximum possible sealing effectiveness in case of a fire event in informal shopping malls. Fire scenarios for nine different fire-source locations having two types of fuel loading in three informal shopping mall designs are numerically analyzed in this study. Against the extremely dense fuel load typically seen in informal shopping malls of different regions, the optimization of operating parameters of the air curtains yields about a 6% to 38% increase in sealing effectiveness in comparison with a commercial air curtain. The optimized air curtains in pairs, at the fire-origin and at the staircase, could confine up to 84% of the oncoming heat and provide crucial improvement in safe evacuation time. The findings of the present study provide a comprehensive understanding of the optimum configuration of the commercially available air curtains for improved effectiveness in heat and smoke confinement in such fire events.

Radio observations of the Black Hole X-ray Binary EXO 1846−031 re-awakening from a 34-year slumber

ABSTRACT We present radio [1.3 GHz MeerKAT, 4–8 GHz Karl G. Jansky Very Large Array (VLA), and 15.5 GHz Arcminute Microkelvin Imager Large Array (AMI-LA)] and X-ray (Swift and MAXI) data from the 2019 outburst of the candidate Black Hole X-ray Binary (BHXB) EXO 1846−031. We compute a Hardness–Intensity diagram, which shows the characteristic q-shaped hysteresis of BHXBs in outburst. EXO 1846−031 was monitored weekly with MeerKAT and approximately daily with AMI-LA. The VLA observations provide sub-arcsecond-resolution images at key points in the outburst, showing moving radio components. The radio and X-ray light curves broadly follow each other, showing a peak on ∼MJD 58702, followed by a short decline before a second peak between ∼MJD 58731–58739. We estimate the minimum energy of these radio flares from equipartition, calculating values of Emin ∼ 4 × 1041 and 5 × 1042 erg, respectively. The exact date of the return to ‘quiescence’ is missed in the X-ray and radio observations, but we suggest that it likely occurred between MJD 58887 and 58905. From the Swift X-ray flux on MJD 58905 and assuming the soft-to-hard transition happened at 0.3–3 per cent Eddington, we calculate a distance range of 2.4–7.5 kpc. We computed the radio:X-ray plane for EXO 1846−031 in the ‘hard’ state, showing that it is most likely a ‘radio-quiet’ BH, preferentially at 4.5 kpc. Using this distance and a jet inclination angle of θ = 73°, the VLA data place limits on the intrinsic jet speed of βint = 0.29c, indicating subluminal jet motion.

Aerodynamic Efficiency Improvement on a NACA-8412 Airfoil via Active Flow Control Implementation

The present paper introduces a parametric optimization of several Active Flow Control (AFC) parameters applied to a NACA-8412 airfoil at a single post-stall Angle of Attack (AoA) of 15∘ and Reynolds number Re = 68.5×103. The aim is to enhance the airfoil efficiency and to maximize its lift. The boundary layer separation point was modified using Synthetic Jet Actuators (SJA), and the airfoil optimization was carried on by systematically changing the pulsating frequency, momentum coefficient and jet inclination angle. Each case has been evaluated using Computational Fluid Dynamic (CFD) simulations, being the Reynolds Averaged Navier–Stokes equations (RANS) turbulence model employed the Spalart Allmaras (SA) one. The results clarify which are the optimum AFC parameters to maximize the airfoil efficiency. It also clarifies which improvement in efficiency is to be expected under the operating working conditions. An energy balance is presented at the end of the paper, showing that for the optimum conditions studied the energy saved is higher than the one needed for the actuation. The paper clarifies how a parametric analysis has to be performed and which AFC parameters can be initially set as constant providing sufficient previous knowledge of the flow field is already known. A maximum efficiency increase versus the baseline case of around 275% is obtained from the present simulations.

A New Hybrid Optimization Method, Application to a Single Objective Active Flow Control Test Case

Genetic Algorithms (GA) are useful optimization methods for exploration of the search space, but they usually have slowness problems to exploit and converge to the minimum. On the other hand, gradient based methods converge faster to local minimums, although are not so robust (e.g., flat areas and discontinuities can cause problems) and they lack exploration capabilities. This article presents a hybrid optimization method trying to combine the virtues of genetic and gradient based algorithms, and to overcome their corresponding drawbacks. The performance of the Hybrid Method is compared against a gradient based method and a Genetic Algorithm, both used alone. The rate of convergence of the methods is used to compare their performance. To take into account the robustness of the methods, each one has been executed more than once, with different starting points for the gradient based method and different random seeds for the Genetic Algorithm and the Hybrid Method. The performance of the different methods is tested against an optimization Active Flow Control (AFC) problem over a 2D Selig–Donovan 7003 (SD7003) airfoil at Reynolds number 6×104 and a 14 degree angle of attack. Five design variables are considered: jet position, jet width, momentum coefficient, forcing frequency and jet inclination angle. The objective function is defined as minus the lift coefficient (−Cl), so it is defined as a minimization problem. The proposed Hybrid Method enables working with N optimization algorithms, multiple objective functions and design variables per optimization algorithm.