Steady Injection Research Articles

Flexible controls to reduce DC voltage deviations in multi‐terminal DC grids

Various disturbances in voltage source converter based high-voltage, multi-terminal DC grids will significantly cause DC voltage deviations when the classical voltage droop control is adopted. The unsatisfactory voltage deviations weaken the voltage regulation ability and increase the risk of instability. Two flexible controls at the top of the classical voltage droop control to reduce voltage deviations are proposed, and the power–voltage (P–V) curves of the classical voltage droop control are translated co-ordinately. Firstly, a global DC voltage oscillation damping control designed based on the Lyapunov theory is proposed for transient voltage deviations. Secondly, a constant weighted voltage control is designed for reducing steady weighted voltage deviations. The steady active power injections keep almost unchanged under proposed controls, consistent with those under only the classical voltage droop control. The stability influence and the power flow impact are carried out to evaluate the proposed controls theoretically. Tests are conducted on a multi-terminal DC grid with five-terminal voltage source converters. Simulation results show the proposed controls' effectiveness and superiority under various fault conditions, including both the outage of a constant power voltage source converter and a droop voltage source converter.

Turbulent Gas in Lensed Planck-selected Starbursts at z ∼ 1–3.5

Abstract Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1–3.5. We analyze 162 CO rotational transitions (ranging from J up = 1 to 12) and 37 atomic carbon fine-structure lines ([C i]) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and [C i] lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed (μ L L IR ( 8 − 1000 μ m ) ∼ 10 13 − 14.6 L ⊙; 〈 μ L M ISM 〉 = (2.7 ± 1.2) × 1012 M ⊙, with μ L ∼ 10–30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( 〈 ΔV turb 〉 ∼ 100 km s−1) and ratios of gas kinetic temperature to dust temperature 〈 T kin/T d 〉 ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, Σ M ISM ∼ 103–4 M ⊙ pc−2 and Σ L IR ∼ 1011–12 L ⊙ kpc−2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.

Critical region in the spatiotemporal dynamics of a turbulent thermoacoustic system and smart passive control

We develop a passive control strategy for suppressing thermoacoustic instability in a bluff-body stabilized premixed turbulent combustor. When the equivalence ratio is varied, there is a transition from combustion noise to thermoacoustic instability via intermittency in the combustor. We perform simultaneous acoustic pressure, 2D-PIV, and CH * chemiluminescence measurements to capture the pressure fluctuations, the velocity field, and the heat release rate (HRR) field during the transition. We measure the spatial distribution of the amplitude of turbulent velocity at the acoustic frequency, time-averaged vorticity, time-averaged HRR, and Rayleigh index and identify various regions of significance. We implement a passive control strategy by targeting these regions with a steady injection of secondary micro-jet of air to optimize the injection location and determine the critical region. Targeting the critical region with secondary air leads to greater than 20 dB suppression of the dominant thermoacoustic mode. We observe that the coherent structure forming from the shear layer following the dump plane gets suppressed, leading to an incoherent spatial distribution of HRR fluctuations. We find that the turbulent velocity amplitude correctly identifies the critical region for optimized passive control during thermoacoustic instability. In contrast, the Rayleigh index identifies the region of the most significant acoustic driving; however, it does not identify the region most sensitive to control. Finally, we extend our analysis by determining the spatial distribution of the Hurst exponent measured from the turbulent velocity field. We show that the Hurst exponent identifies the critical region during thermoacoustic instability and intermittency, unlike the other physical measures. Thus, we develop a smart passive control method by combining the need for finding critical regions in the combustor with the predictive capabilities of the Hurst exponent.

Airfoil leading edge blowing to control bow shock waves

This manuscript presents a detailed characterization of active control of bow shock waves via leading edge injection, including subsonic coolant ejection and the appearance of Coanda effects. The flow phenomena occurring at steady and pulsating flow injection regimes were analyzed using steady and unsteady two-dimensional Reynolds-Averaged Navier Stokes, leading to a precise evaluation of the thermal load and drag reductions. Steady supersonic injection yields the largest abatement in thermal load and aerodynamic drag, while subsonic or fluctuating ones can also provide significant improvements at reduced cooling mass flow rates. Furthermore, a Coanda effect, causing a non-symmetric flow topology, was observed and analyzed for reduced injection port size. This Coanda effect is due to the sudden expansion happening from the injection port to the main flow and it causes the flow topology at the leading edge to become non-symmetric despite the complete symmetry of the problem. This is the first time in the literature such a phenomenon is documented for a supersonic airfoil leading edge injection. Furthermore, it enables the design of novel flow control strategies for the leading edge shock topology and flow structures in supersonic flows.

Film cooling simulation on an entire gas turbine blade with square pulsed coolant injection

Film cooling is an effective method to keep the gas turbine blades from high temperature gases and thermal stresses. Square pulsating film cooling on different sections of a modified NASA C3X blade is numerically investigated. Temperature distribution and film cooling performance are investigated for various blowing ratios of 0.5, 0.75, 1.0, 1.5, 2 and 2.5 in pulse frequency of 50Hz. Reynolds-Averaged Navier-Stokes equations for steady and pulsating injection considered. The shear stress transport ( ) model applied for turbulence effects. Simulations are performed using finite volume method. Obtained results show different findings of pulsating film cooling on the various blade surfaces. For large blowing ratios, averaged pulsed film covering effectiveness at leading edge and pressure side of blade is reduced compared to small and middle values of blowing ratios. This trend is reversed in the suction side. Reynolds number of mainstream has the maximum effect on film effectiveness distribution on pressure section. The averaged centerline pulsed film coolant performance on the pressure surface and leading edge at blowing ratio of 0.5 and for suction side at blowing ratio 2.5 was maximum.

Condition of Occurrence of Large Man-Made Earthquakes in the Zone of Oil Production, Oklahoma

Man-made seismicity is a response of the brittle crust to fluid injection at depth and to the subsequent increase in pore-pressure and stress field perturbations. In Oklahoma, where the sharp increase in earthquake rate correlates with injection operations, we show that the earthquake-size distribution can differ significantly on the volume of injected fluid. The size distribution of M 2) may be documented for larger magnitude ranges. This change shows statistically significant positive dependence on injection activity. In addition, largest events occur at the border of the injection area at some distance from massive injection, and in the periods of steady injection rate. These observations suggest that a deficit of large induced earthquakes under conditions of high injection rate can be accompanied by an overall increase of natural seismicity along pre-existing faults in the surrounding volume, where large events are more likely to be triggered over longer space-time scales.

Altered neuronal excitability in a Hodgkin-Huxley model incorporating channelopathies of the delayed rectifier potassium channel.

Channelopathies involving acquired or genetic modifications of the delayed rectifier K+ channel Kv1.1 include phenotypes characterized by enhanced neuronal excitability. Affected Kv1.1 channels exhibit combinations of altered expression, voltage sensitivity, and rates of activation and deactivation. Computational modeling and analysis can reveal the potential of particular channelopathies to alter neuronal excitability. A dynamical systems approach was taken to study the excitability and underlying dynamical structure of the Hodgkin-Huxley (HH) model of neural excitation as properties of the delayed rectifier K+ channel were altered. Bifurcation patterns of the HH model were determined as the amplitude of steady injection current was varied simultaneously with single parameters describing the delayed rectifier rates of activation and deactivation, maximal conductance, and voltage sensitivity. Relatively modest changes in the properties of the delayed rectifier K+ channel analogous to what is described for its channelopathies alter the bifurcation structure of the HH model and profoundly modify excitability of the HH model. Channelopathies associated with Kv1.1 can reduce the threshold for onset of neural activity. These studies also demonstrate how pathological delayed rectifier K+ channels could lead to the observation of the generalized Hopf bifurcation and, perhaps, other variants of the Hopf bifurcation. The observed bifurcation patterns collectively demonstrate that properties of the nominal delayed rectifier in the HH model appear optimized to permit activation of the HH model over the broadest possible range of input currents.

Polymeric Membrane Sensors for Batch and Flow Injection Potentiometric Determination of Procainamide

Three new potentiometric membrane sensors responsive to procainamide hydrochloride (PR) were constructed and their general performance characteristics were determined. The sensors were constructed from PR ion-association complexes with tetraphenylborate (NaTPB) (1), phosphomolybdic acid (PMA) (2) and phosphotungstic acid (PTA) (3) as exchange sites in a polyvinyl chloride (PVC) matrix. The sensors exhibited stable, rapid and near-Nernstian properties for PR at concentrations of $1\times 10^{{-2 }}$ – $4\times 10^{-6}$ , $1\times 10^{-2}- 5\times 10^{-6}$ , $1\times 10^{-2}$ – $6\times 10^{-6}$ M at 25 °C with cationic slopes of 58 ± 0.5, 57 ± 0.5 and 56 ± 0.5 (mV/decade) for sensor 1, 2 and 3 respectively. The response time of the sensors was 20s in the optimum pH range of 4-8. The sensors were used in steady state and flow injection mode (automated system). Method validation revealed the sensors have high selectivity, low detection limits, long life, wide dynamic ranges as well as high accuracy and precision. Direct determination of 5- $2000~\mu \text{g}$ /ml of PR in solution returned average recoveries of 98.5%, 99.0% and 98.5% and mean relative standard deviations of 1.6%, 1.6% and 1.8% at $200.0~\mu \text{g}$ /ml for sensor 1, 2 and 3 respectively. Further, detection of procainamide in spiked urine exhibited favorable relative standard deviation (1.60-1.76%) and high recovery (98.83-99.26%). The sensors were used as end-point indicators for titration of procainamide with NaTPB.

Effect of frequency during cyclic hydraulic fracturing and the process of fracture development in laboratory experiments

Cyclic injection in hydraulic fracturing has been reported to reduce the level of induced seismicity compared to the conventional continuous injection. We investigate the evolution of acoustic emission (AE) activity, hydraulic energy, fracture area, and fracture development for cyclic injection schemes with different cycle time durations (td) at a repeated maximum cyclic pressure through laboratory experiments. These test were compared with a case under conventional continuous injection at an injection rate of 50 mm3/s. Pocheon granite samples with an outer diameter of 50 mm, height of 100 mm, and an inner borehole of 8 mm were used. The maximum pressure of 5.5 MPa for each cycle represents approximately 77% of the average breakdown pressure from continuous injection cases. Four td values of 30 s, 60 s, 120 s, and 240 s were selected. The results show an exponential decrease in the number of cycles until failure with increasing td. Similarly, the total number of AEs, the peak AE rate, and the cumulative AE energy also decreased with increasing td. These values contrasted with those for continuous injection which reported the lowest number of AEs, and the highest cumulative AE energy. The td influence was also evident on the AE occurrence, with fewer high amplitude AEs at a high td, and all lower than continuous injection. In general, the hydraulic energy and cumulative AE energy decreased with increased with increasing td, although a slight deviation was related to the total testing time. The fracture areas during cyclic injection reported a positive correlation with the cumulative AE energy. Moreover, detailed analysis of the instantaneous injection rate, and the cumulative AEs suggested a three-stage damage process, which was supported with X-ray computed tomography observations. The second stage was characterized by a steady linear injection rate increase, and its slope correlated with the fatigue life or number of cycles to failure. Finally, based on the injection rate evolution, an interpretation of the damage evolution and fracture onset during cyclic hydraulic fracturing could be made.

Study and Practice of stabilized injection technologies in injection well life cycle

The technologies to steady pressure and injection rate and that to reduce pressure and increase injection rate are along with multiple stages of secondary and tertiary oil recovery. The ongoing injection process will subject most wells to pressure rise, reduced injection volume, fouling and plugging of reservoir, and corrosion of tubing string. In this paper, a portfolio of feasible measures can be provided for the steady injection in injection well life cycle by taking a closer look at cleaning & anti-swelling & anti-migrating technology, interlayer pressure influence balancing technology, slow releasing solid acid unpowered acidizing technology, low damage & low reaction rate acidizing technology, and degrading & acidizing technology for polymer injection wells.

Using High-Frequency Pulsed Supersonic Microjets to Control Resonant High-Speed Cavity Flows

A novel actuator concept is evaluated in a series of active flow control experiments on a resonant high-speed cavity flow. The actuator generates pulsed supersonic microjets by using the resonance of an impinging microjet source, and with smart materials incorporated into its design, the actuator’s resonant frequency can be actively controlled. The actuator was designed such that its resonant frequency would lie within the range of predicted cavity resonance. Results from Mach 1.5 flow over a cavity of length are presented, and the actuator’s performance is evaluated across three modes of operation: pulsed, active pulsed, and steady. In the active pulsed mode, the smart materials are used to actively vary the actuator’s resonant frequency, enabling frequency modulation of the actuator’s output. When the actuator operates in both pulsed modes, the amplitude of the dominant peak in the cavity’s unsteady pressure spectra is reduced by as much as 7 dB. However, steady microjet injection yields more effective control. The dominant peak is substantially attenuated (by 25 dB) in this mode of operation. The effectiveness of the steady mode is attributed to higher momentum flux that can be attained in contrast to the pulsed modes of operation.

Effects of temperature and density evolution in MHD simulations of HIT-SI

The helicity injected torus-steady inductive (HIT-SI) experiment uses steady inductive helicity injection to form a spheromak equilibrium and sustain the structure against resistive decay. Helicity injection is performed using two half-tori “injectors” connected to the main plasma volume, whose fields are oscillated in an AC manner. The properties of the sustained spheromak equilibrium have been experimentally observed to vary with the frequency of the injector oscillation, producing higher current gains and more-symmetric and outwardly shifted current centroids with higher frequency. A computational scan of injector frequency using the 3D MHD code PSI-Tet, which models the entire HIT-SI plasma volume including the injectors, has been performed, including a comparison of the results using the full Hall MHD model to those obtained using a simplified “zero-beta” (constant temperature and density) model. The results of both PSI-Tet models are also compared with experimental data and with simulations using the NIMROD code, which does not model the injector regions. The results of the PSI-Tet simulations show that the average temperature and current gain increase with injector frequency, in agreement with experimental trends. The simulations also show qualitative changes in the dynamics of several quantities with increasing injector frequency, such as density oscillations and current evolution. However, the outward shift and symmetrizing of the current centroid, observed experimentally, are not observed in these MHD simulations, indicating that unresolved or excluded dynamics may be important.

Effect of Valve Opening Manner and Sealing Method on the Steady Injection Characteristic of Gas Fuel Injector

The steady-state injection characteristic of gas fuel injector is one of the key factors that affects the performance of gas fuel engine. The influences of different injection strategies, such as different injection angles and different injection positions, on the mixing performance in gas-fueled engine have been emphasized in previous literatures. However, the research on the injection characteristics of the gas fuel injector itself are insufficient. The three-dimensional steady-state computational fluid dynamics (CFD) models of two kinds of injectors, in different opening manners, and the other two kinds of injectors, in different sealing methods, were established in this paper. The core region speed, stagnation pressure loss and mass flow rate were compared. Additionally, the effective injection pressure (EIP) concept was also used to evaluate the injection efficiency of gas fuel injector. The simulation results show that the jet speed of the pull-open injector is higher than the push-open injector under the same operating conditions. The injection efficiency of the pull-open valve is about 56.0%, while the push-open valve is 50.3%. In general, the steady-flow characteristic of the pull-open injector is better than that of the push-open one. The injection efficiency of the flat sealing injector is 55.2%, slightly lower than the conical sealing method.

Automatic stability control using tip air injection in a multi-stage axial flow compressor

Automatic stability control is experimentally investigated using tip air injection in a multi-stage axial flow compressor. The warning signal is obtained according to the auto- and cross-correlation algorithm integrated in the digital signal processing controller for online monitoring wall pressure signal at different stages. It is used as a feedback signal to drive the discrete proportional jet valves. The control law depends on the stall margin improvement (SMI) versus injected momentum ratio relationship. The real-time detection algorithms based on the correlation theory are experimentally studied using a collection of pressure transducers installed symmetrically on the casing at different stages. The results reveal that because of the initial appearance of stall inception at the first stage, which induced a stall in all stages of the compressor, only the correlation coefficient detected at the first stage exhibits a decreasing trend in the throttling process. Moreover, only the tip air injection at the first stage can obtain a large SMI. Therefore, the correlation coefficient detected at the first stage is used as the feedback signal in the controller after verifying the influence of injected air on the correlation coefficient. Compared with steady injection, the proposed automatic stability control can save energy when the compressor is stable and provide protection to extend the stall margin when close to the stall point. With a nearly equal SMI as the steady injection (the maximum SMI is 20%), the energy of the active injected air is approximately one-fifth of the steady injection. This active control can fully consider the failure control such that when the control system is inoperative, the aero-engine continues safe operate under normal circumstances.

Permeability measurement and discovery of dissociation process of hydrate sediments

The study on the permeability of methane hydrates in fine quartz sands contributes to the accurate prediction of gas/water production and can effectively express the characteristics of fluid migration. In this study, the water effective permeability (kw) of methane hydrates in three fine quartz sands containing various hydrate saturation (SH) were carried out under steady water injection and production. Experimental results indicated that the effect of particle sizes on kw was significant even though the difference in the average particle size of three fine quartz sands was relatively limited. The differential pressure of the hydrate sediments was completely recorded during permeability measurement, and the stabilization and decomposition process of hydrate could be clearly represented by differential pressure. The kw increased rapidly with the decomposition of hydrate and the appearance of flow channel in the hydrate sediments. Hydrate dissociation process was recorded in situ by Cold Field Emission Scanning Electron Microscopy (CFE–SEM), the dissociation of hydrates in pore space was clearly visible, and the hydrates in pore space were first dissociated into many small regions. A new reduction model between water relative permeability (krw) and SH was proposed on the basis of experimental results, and the experimental data fitted well with hydrates occupying pore centers. The effect of particle sizes on krw was eliminated, the Archie saturation exponent n tended to increase with the increase of SH, and n was recommended between 20 and 30.

EXPERIMENTAL STUDY ON THE EFFECT OF CAVITATION ON PRESSURE FLUCTUATIONS IN OPTICAL DIESEL NOZZLES AND SPRAY CHARACTERISTICS

The influence of the cavitation effect on the diesel engine nozzle is based on the following aspects: flow and spray characteristics, cavitation erosion on the nozzle wall, and pressure fluctuations of diesel fuel in the system. The first two have been extensively studied, but the research on the third one is rather limited. In this article, the synchronous acquisition, data processing system of cavitation, pressure fluctuations of diesel fuel, and spray characteristics inside the transparent nozzle were examined, then the direct correspondence among pressure fluctuations and cavitation phenomenon was explored. Experimental studies under steady injection pressure and fixed needle lift show that: during the process of transforming hole-to-hole string cavitation to needle-originated string cavitation, the pressure fluctuation amplitude increases significantly. String cavitation under low pressure is easily converted into geometry-induced cavitation due to morphological instability, which has a large disturbance to the spray cone angle. String cavitation under high pressure is more intense with the pressure fluctuation is relatively large and its intensity is weaker than the geometry-induced cavita-tion intensity under the same pressure; however, both the pressure fluctuation amplitude and spray cone angle are much larger. The peak pressure of string cavitation is higher than that of geometry-induced cavitation. In the process of the disappearance, fracture, and fusion of string cavitation, the pressure fluctuation amplitude increases significantly. The results of this experiment play a crucial role in the effective control of pressure fluctuations in the system.

Modulation of aerodynamic characteristics of a finite wall-mounted square cylinder through steady jet injection

This paper presents the results of an experimental study that investigates the flow behavior around a finite wall-mounted square cylinder (with the aspect ratio of AR = 7) subjected to a steady jet issued from the cylinder’s front face. Two wavy and continuous jets were considered to examine the jet velocity distribution effect. The wind tunnel measurements consist of smoke flow visualization, mean drag force, mean surface pressure, and velocity data obtained from hotwire probe, mostly at Reynolds number (Red, based on the cylinder width and inlet velocity) of 1.2 × 104. The ratio of the jet flow to the freestream, Г, was changed as 0 ≤ Г < 5. Both the wavy and continuous jets reduce the downwash flow contribution with the flow from the lateral faces. An increase of Г continuously amplifies this effect, and improves the flow control performance in drag reduction. The maximum pressure drag reduction of 29% and 16% were obtained for the wavy and continuous jets, respectively. Two characteristic continuous jet flow modes, namely deflected jet (Г < 1) and deflected oscillating jet (1 < Г < 2), were identified. The both continuous jet deflection mode have a leading role in the pressure reduction on the front face, and subsequently in drag reduction. Oscillation of the deflected continuous jet at high-Г also significantly increases the vortex shedding frequency in the upper half of the cylinder, and makes the mean wake flow asymmetrical. On the other hand, the base pressure recovery is the major reason for the drag reduction when the wavy jet is applied. The wavy jet shows a slight deflection at high-Г; however, the mean wake flow remains symmetrical. Finally, the influence of jet flow control on the flow topology was discussed.

Experimental study on recharge capacity of a mixed well injection in Xi’an

The over-exploitation of groundwater can be controlled and prevented by using mixed well to recharge groundwater. A seepage model of semi-confined aquifers was established for simulating recharge well in a cone of depression. Two mathematical expression formulas were proposed for estimating recharge capacity. To analyze the response of recharge capacity, stepwise injections were introduced. It can be pointed out that recharge capacity increases with that of injection flow; moreover, it tends to attenuate during steady injection, which is closely related to injection flow. An attenuation equation of recharge capacity was constructed finally. Recharge capacity was not related to injection mode. The results indicate that under similar conditions, recharge capacity of a mixed well was about one-third of pumping capacity. A minimum value of recharge capacity was maintained with constant injection. Mixed wells were used to recharge and recover groundwater from the cone of depression.

Flow structures and thermal field with modulated jet near the semi-circular leading edge

Influence of external modulation on unsteady flow and heat transfer near the leading edge of a constant thickness aerofoil has been described through large eddy simulation. This is a simplified approach to study film cooling activities near the leading edge of a turbine blade. Discrete jets, which are forced at a Strouhal number (St) of 0.37 with an averaged blowing ratio of unity, are ejected normally from a series of film cooling holes to a separated boundary layer. The results are compared against the corresponding steady injection. Larger coherent structures appear for a forced jet with an augmented vortex dynamics resulting in high jet lift-off, earlier break down, enhanced mixing with the cross flow and dilution of coolant layer. Resolved hairpins, which are the signature of coherent structures, illustrate that the vorticity and thermal field are highly correlated. Furthermore, evolution of hairpins and their advection control scalar transport and mixing. In brief, the modulation of coolant jet near the leading edge appears not beneficial for the combination of blowing ratio and frequency considered here.

Impact of tab location relative to the nozzle exit on the shock structure of a supersonic jet

This paper presents an experimental study of a Mach 2.0 jet manipulated using rectangular tabs to understand the mixing enhancement at the overexpanded and perfectly expanded state of the jet. This paper also compares the mixing effectiveness of the tabs in comparison with the fluidic injection reported in our previous work [Kumar et al., “Empirical scaling analysis of supersonic jet control using steady fluidic injection,” Phys. Fluids 31(5), 056107 (2018)]. Tabs used in this investigation were rectangular strips of aspect ratio, AR, 2 (AR = length of the tab/width of the tab) and are positioned at 0De, 0.25De, 0.5De, and 0.95De (De is the nozzle exit diameter) downstream of the nozzle exit. Pitot pressure measurements were carried out along the jet centerline and in the radial directions to examine the supersonic core length (Lc*) and jet spread, respectively. The jet stream has been visualized using the shadowgraph technique in the orthogonal planes of the manipulated jet. The mixing capability of the manipulated jet quantified based on the reduction in supersonic core length ΔLc* strongly depends on the control technique and its location along the downstream direction. Three types of flow categories are identified, i.e., the “jet bifurcation,” “complex and strong shock-cell structure,” and “weak shock structure,” which depend on the tab location (xt*) and account for the jet mixing. The present study reveals that the tabs should be positioned downstream of the first shock crossover point which results in shorter core length and, hence, higher jet mixing. A conceptual model of the flow structure under control is proposed.