Main Jet Research Articles

Experimental investigation of film cooling from compound angle holes supplemented by secondary holes

Gas turbine performance largely depends on the inlet temperature. Higher the inlet temperature better is the performance of the turbine which in turn may adversely affect the turbine blades. Film cooling techniques are used to protect the turbine from hot gases. In this study, secondary holes were added to the compound angle holes to improve the turbine performance by enhancing the film cooling. Four blowing ratios were considered in this study. A Baseline case with zero orientation angle and 30° inclination angle was used as a reference. To analyze the film cooling effectiveness with reference to the Baseline case, four different cases (cases with 30° and 60° orientation angles with and without secondary holes) were studied. Thermocouples and infrared camera were used to study the effectiveness of the film cooling. Infrared camera shows its ability to capture the temperature variation in a finite area due to its high resolution. The results show that the cases with compound angle have higher effectiveness compared to the Baseline case. Also, providing secondary holes helps keep the main hole jet to move beside the test surface and results in higher effectiveness especially at high blowing ratios.

An experimental model with passively variable stiffness to investigate the effect of body stiffness on the fish fast-start maneuver

We present an experimental model to investigate the influence of body flexibility on the fast-start response. The model is fabricated with a variable stiffness, characterized by the direction of applied force. When the fluid force is applied in one direction, the structure acts flexibly and bends, and when the force is applied in the opposite direction, it remains rigid. The structure is rotated from its initial straight position in its flexible direction to a given angle (Stage 1), and then it is rotated back in its rigid direction to an angle in the opposite direction (Stage 2). The wake patterns are studied with bubble image velocimetry (BIV) showing that the main propulsive jet, previously observed in the live fish fast-start, can be produced using this model. Based on our results, we determine that flexibility during Stage 1 and increased rigidity during Stage 2 predict velocity profiles and escape angles consistent with those observed in live fish. A parametric study on the effect of angular velocity and total swept angle on the produced power reveals that the magnitude of swept angle is critical to formation of the propulsive jet. The peak power transfer is found to be more sensitive to increasing the angular velocity for larger swept angles, where a complete jet is already formed.

The Giant Herbig–Haro Flow HH 212 and Associated Star Formation

The bipolar jet HH 212, among the finest collimated jets known, has so far been detected only in near-infrared H$_2$ emission. Here we present deep optical images that show two of the major bow shocks weakly detected in optical [SII] emission, as expected for a bona fide Herbig-Haro jet. We present widefield H$_2$ images which reveal two more bow shocks located symmetrically around the source and along the main jet axis. Additionally, examination of Spitzer 4.5 $\mu$m images reveals yet another bright bow shock further to the north along the jet axis; no corresponding bow shock is seen to the south. In total, the HH 212 flow has an extent of 1050 arcsec, corresponding to a projected dimension of 2.0 pc. HH 212 thus joins the growing group of parsec-scale Herbig-Haro jets. Proper motion measurements indicate a velocity of about 170 km/sec, highly symmetric around the source, with an uncertainty of $\sim$30 km/sec, suggesting a probable age of the giant HH 212 flow of about 7000 yr. The jet is driven by a deeply embedded source, known as IRAS 05413-0104. We draw attention to a Spitzer near- and mid-infrared source, which we call IRS-B, located only 7 arcsec from the driving source, towards the outskirts of the dense cloud core. Infrared photometry and spectroscopy suggests that IRS-B is a K-type star with a substantial infrared excess, except that for an extinction of A$_V$ = 44 the star would have only a weakinfrared excess, and so in principle it could be a K-giant at a distance of about 2 kpc.

Experimental Research on Wall Pressure Distribution in C-D Nozzle at Mach number 1.1 for Area Ratio 3.24

In this experimental investigation the work reported is about the influence of control on the flow field in the suddenly expanded duct at low supersonic Mach number. A Convergent-divergent (CD) nozzle was designed and fabricated out of brass material assembled with the suddenly expanded duct which was also made of brass material. At the re-circulation zone, the flow field was controlled by using the micro jets of 1 mm diameter as an orifice and the control was arranged at an interval of 90 degrees at 6.5 mm from the central axis of the main jet. The measured wall pressure distribution was presented for Mach number 1.1 for the duct diameter of 18 mm leading to the area ratio 3.24. The L/D ratio of the duct was varied from 1 to 10, and the nozzle pressure ratio (NPR) considered for the experiments was from 3, 5, 7, 9 and 11. The present results have demonstrated that the micro jets do not influence the flow field in the duct adversely and the flow field remained identical in the presence of control or absence of control

Jet-Flipping in Scour Hole Downstream of Unsubmerged Weir with Apron

AbstractAn apron downstream of an unsubmerged weir can cause the main jet to flip up and down cyclically in a local scour hole, significantly influencing the scouring process. This behavior was exp...

Influence of Control Mechanism on the Flow field of Duct at Mach 1.2 for Area Ratio 2.56

In this paper, the outcome of the experimental investigation and the flow field development in the duct at supersonic Mach number of 1.2 is presented. The experiments were conducted at various NPR which covers the condition of correct expansion and under expansion. A Convergent-divergent (C-D) nozzle which is connected with the suddenly expanded duct of the diameter of 16 mm of area ratio 2.56. The recirculation zone is controlled by using the microjets of 1 mm of orifice diameter which are placed at 90 degrees interval at 6.5 mm from the central axis of the main jet. The L/D of the duct was used in the investigation was from 1 to 10, and the NPR at which the experiments were conducted considered are in the range from 3, 5, 7, 9 and 11.

Molecular Modeling and Opioid Receptor Binding Affinity of New Substituted Morphine Derivatives

In this paper, the outcome of the experimental investigation and the flow field development in the duct at supersonic Mach number of 1.2 is presented. The experiments were conducted at various NPR which covers the condition of correct expansion and under expansion. A Convergent-divergent (C-D) nozzle which is connected with the suddenly expanded duct of the diameter of 16 mm of area ratio 2.56. The recirculation zone is controlled by using the microjets of 1 mm of orifice diameter which are placed at 90 degrees interval at 6.5 mm from the central axis of the main jet. The L/D of the duct was used in the investigation was from 1 to 10, and the NPR at which the experiments were conducted considered are in the range from 3, 5, 7, 9 and 11

Using Mobile Health Technology to Improve Well-Being in Caregivers of Patients with Bipolar Disorder: Poster Abstract Submission

A piloted, partially premixed, liquid-fueled swirl burner is operated at high pressure (1 MPa). High-speed (6 KHz) stereoscopic PIV is used to investigate the characteristics of the stagnation line separating the pilot jet and the central recirculation zone (CRZ) with varying pilot-main ratio and global equivalence ratio. The mean curvature of the stagnation line displayed a large spatial scale pattern that was present for all operating conditions. All three components of velocity, in-plane shear, and swirling strength are conditioned upon the instantaneous stagnation line. Mean distributions of the velocity normal to the stagnation line show that velocity is oriented towards the CRZ when the stagnation line is found nearer the centerline of the combustor. The conditioned out-of-plane velocity (w) shows a distinct concentration of large mean and fluctuation RMS values towards the center of the measurement domain. Varying fuel flow does not significantly change this spatial structure, only the magnitudes of the w statistics. The in-plane shear stress was the largest for the pilot biased condition as a stronger shear layer develops. For the leanest flame, large fluctuation RMS values of shear stress were confined to a region where the pilot jet begins to interact more heavily with the main jet. Operating with less pilot fuel flow enhanced the mean conditional swirling strength indicating that the pilot shear layer was shedding more intense eddies. Disregarding spatial relations, a scatter plot of w, shear stress, and swirling strength displayed trends between the variables. The largest swirling strength values coincide with highest magnitude shear stresses and the widest range of w. These conditioned statistics highlight how certain aspects of the combustor flow field are invariant with fuel distribution. This is desirable for aeropropulsive combustors that must maintain stable ignition from a range of conditions from landing/take-off to cruise.

Influence of flow parameters on the dynamic performance for the supersonic jet element

The influence of the inlet and outlet flow parameters on the dynamic performance for the supersonic jet element have been investigated numerically in details. And the precision and errors accumulation of the numerical method has also been estimated. The influence of the main jet pressure and the mass flow rate of the control flow on the output thrust as well as the switching time have been deeply studied. The results have shown that increasing the mass flow rate of the control flow can shorten the switching time and increase the effective thrust slightly, but it also can enhance the unsteadiness of flow in the wall-attached work state but decrease the energy utilization rate of the supersonic jet flow component. The effective thrust generated by the cold air is larger than the gas work medium. And the switching time for the gas working medium is also shorter, which is more conducive to the completion of the switch process. The vortical structures at different switching time together with the force variations inside the jet element have been obtained computationally and analyzed in details.

New look at the water exchange between the Arctic and North Atlantic in Iceland basin

Based on the multi-year current observations along 59.5 N in the Subpolar North Atlantic multi-jet transport of arctic water along Reykjanes Ridge eastern slope producing Iceland-Scotland overflow water (ISOW) in Iceland Basin is revealed. Main jet properties as well as their contribution to the deep water transport are discussed.

Adjustable Frequency Fluidic Oscillator with Supermode Frequency

This Paper introduces a feedback-type fluidic oscillator design with adjustable frequency at a constant flow rate. Details of the internal and external flowfields were revealed by numerical simulations with the help of frequency measurements and visualizations. Fluidic oscillator’s internal flowfield was manipulated by fluid injection from the islands of the oscillator into the interaction chamber. The interaction between the oscillator’s main jet and the control jets was observed to generate vortices in the mixing shear layers of the jets due to the Kelvin–Helmholtz instabilities. These vortices started to govern the separation bubble characteristics as the control flow rate was increased. After a certain control flow rate threshold was exceeded, the oscillations were no longer controlled by the feedback flow. Instead they were controlled by the vortices generated by the instabilities, resulting in much higher frequencies. These high-frequency oscillations in the supermode control flow rates were determined to be as high as five times the regular frequency of the oscillator. However, a reverse relationship between frequency and sweep angle was also identified. Depending on the amount of control flow at a constant total flow rate, three regions and five cases distributed in these regions are reported.

Empirical scaling analysis of supersonic jet control using steady fluidic injection

Following our previous work [Kumar et al., “Fluidic injectors for supersonic jet control,” Phys. Fluids 30(12), 126101 (2018)], we experimentally investigate the effect of fluidic injection on the mixing enhancement of a Mach 2.0 jet. The mass flow rate ratio Cm of the injectors to that of the main jet and the expansion ratio pe/pa (where pe and pa are the nozzle exit and atmospheric pressures, respectively) to understand the mixing capability at design and off-design conditions are examined in detail. Extensive Pitot pressure measurements are performed along the jet centerline, and 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* exhibits a strong dependence on Cm and pe/pa. Empirical scaling analysis of the jet control reveals that the relationship ΔLc* = f1(Cm, pe, pa, D, d) may be reduced to ΔLc* = f2(ξ), where f1 and f2 are different functions and the scaling factor ξ = MRpe/pa(Dd)1.3, where MR is the momentum ratio of the injector to the main jet, D and d are the nozzle exit diameter and the injector exit diameter, respectively. The scaling parameter ΔLc* = f2(ξ) provides important insights into the jet control physics.

Computational research on film cooling performance of different shaped holes with backward and forward injection

The present work has been performed to evaluate the effect of three shaped holes (cylindrical hole, expansion-shaped hole and fan-shaped hole) with forward injection and backward injection on film cooling effectiveness on the adiabatic wall flat plate. All the cases are computed under eight blowing ratios (M) = [0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0]. The results show that for film cooling hole structure with backward injection, a pair of rotating vortex is formed at the outlet of film cooling hole. Differing from the classical counter rotating vortex pair (CRVP) found in each hole with forward injection, the vortexes are expanded away from the test wall under the function of transverse main flow and are broken quickly. It indicates that the rotating vortex pair does not promote the mixing of main flow and jet flow. The uniformity of local film cooling effectiveness of the hole with backward injection is higher than that of the hole with forward injection. In terms of the spatially averaged film cooling effectiveness with a certain hole shape, the value under backward injection exceeds that under forward injection at a certain point: (1) M=0.5 for cylindrical hole, (2) M=0.75 for expansion-shaped hole and (3) M=1.25 for fan-shaped hole. The comparison of the calculation results of different holes with backward injection shows that in the case of high blowing ratio, a uniform distribution with higher film cooling effectiveness is easier to achieve with fan-shaped hole.

Cavitation and flow forces in the flapper-nozzle stage of a hydraulic servo-valve manipulated by continuous minijets

Electro-hydraulic servo-valves play key roles in modern electro-hydraulic power systems in many industrial applications. As one of the widely used hydraulic servo-valves, cavitation in the flapper-nozzle servo-valve could produce deleterious effects of noise, flapper vibration and cavitation erosion. In this work, a numerical investigation has been conducted on the manipulation of the flapper-nozzle pilot valve using continuous minijets. Two minijets are symmetrically deployed around the main jet of each nozzle. Vapor fraction and flow forces under the effect of the continuous minijets are compared in detail between the traditional nozzle and the nozzle with the minijets. It is found that cavitation in the flapper-nozzle stage is greatly weakened under the effect of the continuous minijets. The remarkable drop in the radial jet velocity results in the suppression of the swirling structures in the annulus, which may be responsible for the cavitation reduction. The variation trend of the flow forces with the inlet pressure remains unchanged while the magnitude of the flow forces is varied slightly, depending on the various surfaces of the flapper.

Geological and hydrological studies in the Northern Atlantic in 2017 on a section at N59°30’ (68th сruise of the research vessel Akademik Mstislav Keldysh)

The first results of the multidisciplinary expedition aboard the RV «Akademik Mstislav Keldysh» to the North Atlantic in July 2017 are given. Continuation of deep convection in the Irminger Sea to a depth of 1500 m, which began in 2015, is discovered. New information is provided on the structure of the main jets of the North Atlantic Current in the Iceland basin and in the Irminger Sea (Irminger Current), as well as the East Greenland Current. New samples of atmospheric aerosols, suspended particulate matter and bottom sediments are collected. New data on the particle fluxes have been obtained using sediment traps.

Measurement of two-dimensional heat transfer and flow characteristics of an impinging sweeping jet

This study experimentally explores the two-dimensional heat transfer characteristics of an impinging sweeping jet generated from a feedback–channel-type fluidic oscillator. The results were compared to those of a steady square jet. A phosphor thermometry technique was used to measure the surface temperature field on an aluminum plate for different Reynolds numbers and jet-to-wall spacing. A two-dimensional planar Particle Image Velocimetry (PIV) measurement of the sweeping impinging jet was also conducted to couple the flow characteristics and heat transfer performance. The local Nusselt number distributions on the flat plate were evaluated by converting the temperature fields. The heat transfer performance of the sweeping jet is much higher than that of the steady jet because the sweeping motion of the jet induces significant turbulent flow and clearly improves the thermal transport near the impingement plate. However, when the jet-wall spacing becomes greater than 5, the heat transfer performance of the sweeping jet drastically decreases due to the reduced impinging velocity, and the heat transfer of the steady square jet surpasses that of the sweeping jet. In the ensemble averaged velocity fields, two main jet streams are ejected to the plate like oblique impinging jets near the sidewalls of the exit because the jet flow is attached to sidewall one or the other for more than 70% of an oscillation period. There was high similarity between the ensemble averaged velocity profiles and the Nusselt number profiles.

Numerical Experiments for the Case of Acceleration of a Body of Revolution

Reducing the aerodynamic drag of bodies of revolution at supersonic speeds due to the creation of a bottom thrust is an important subject of aeromechanics. In the framework of this problem, it is proposed to perform numerical experiments on a model with a detachable bottom. It is assumed that the detachable bottom is affected by the main air flow jets separating from the surface of the body of revolution. The gas is reflected from the bottom and acts on the body of revolution, creating a bottom thrust and accelerating it.

Intermittent round jet controlled by lateral pulse-modulated synthetic jets

A round air jet was actively controlled by a pair of lateral control jets. The control jets were generated by a pair of opposing synthetic jet actuators, which were driven by the pulse-modulated sinusoidal signal. Two carrier frequencies were tested, namely 160 Hz and 840 Hz. Moreover, control jets driven by un-modulated sinusoidal signals were also tested. An unforced continuous jet was used as the reference case, and for all cases, the Reynolds number of the main round jet was 1570 (related to the nozzle exit diameter of 10 mm). Experiments (flow visualization and hot-wire anemometry) revealed that the flow control caused a suppression of the jet core and a more rapid jet flow decay. In addition, the pulse modulation caused jet intermittency that was distinguished by the periodicity of the time-averaged and fluctuating velocity components. For the case of the lower carrier frequency of 160 Hz, a flapping motion of the controlled jet occurred and the jet formed a zigzag pattern.

Cavitation reduction of a flapper-nozzle pilot valve using continuous microjets

The flow cavitation in the flapper-nozzle stage is one of the main factors that produce the flapper vibration and thus deteriorate the performance of the flapper-nozzle servo valves. This work proposes a novel method, deploying two continuous microjets around the main jet of each nozzle, to suppress the cavitation. The cavitation reduction using continuous microjets is numerically examined in detail by comparing the vapor fraction with and without the microjets at different inlet pressure, housing diameter and the null clearance. The mass flow rate measurements and the flow visualization are conducted to validate the numerical simulation. It is found that the cavitation in the flapper-nozzle stage is significantly reduced under the effect of the continuous microjets. And the flow cavitation exhibits a great dependence on the inlet pressure, housing diameter and the null clearance. In the traditional flapper-nozzle structure, the cavitation is strongly enhanced at high inlet pressure, small housing diameter or large null clearance. Nevertheless, the cavitation in the flapper-nozzle structure with the microjets is still remarkably suppressed at the same condition. This indicates that the continuous microjets are highly effective in reducing the cavitation of the flapper-nozzle valve.

Влияние вдува малоразмерных струй различных конфигураций на структуру и акустическое излучение сверхзвуковой струи

The work is devoted to experimental study of the structure and acoustic radiation of a supersonic underexpanded jet Ma = 1, Npr = 5 with the presence of vortexgenerators in the form of small-sized jets injections. Ten different configurations were tested, in which following the gas-dynamic and geometrical parameters of the microjets were changed one by one: microjets pressure, the injection distance from the main nozzle section, azimuthal, tangential, and axial angles of micronozzles inclination. The flow visualization, azimuthal Pitot pressure profiles and characteristics of jet noise in the far field were obtained. It has been revealed that the injection of microjets in general leads to an increase in the jet long-range and a decrease in its mixing. The advantageous parameters of the microjets injection for reducing the jet acoustic emission are the injection point vicinity to the main nozzle section, micronozzles inclination to main jet axis and the small tangential angle of micronozzles. The micronozzles quantity effect is non-linearly in relation to the structure and the jet noise. The average pressure measuring distribution near artificial longitudinal vortices in a jet stream cannot predict the characteristics of its mixing and acoustic radiation.