Jet Flow Research Articles

Noise Reduction Using Synthetic Microjet Excitation in Supersonic Rectangular Jets

This work explores a potential methodology for rectangular jet noise reduction that employs nozzle unsteady microjet excitation. Using high-fidelity computational studies and spectral analyses, major jet noise sources impacted by the applied actuation are identified. A heated supersonic rectangular jet is considered with a nozzle aspect ratio of 2:1 at a Mach number of 1.5. The current study essentially validates the hypothesis of a previous reduced-order analysis that predicted jet noise reduction through jet excitation at the harmonic or subharmonic of the dominant frequency associated with jets’ large-scale structures. Such noise reduction was attributed to the excitation-induced nonlinear energy exchange between the coherent modes. In the current study, the synthetic microjet actuation of the jet plume shear layer using 1% of the jet mass flow rate is implemented at the excitation ports located at the nozzle lip and directed along the jet axis. A resulting jet noise reduction of up to 4 dB at the peak radiation angle is predicted. An analysis of the near-field Spectral Proper Orthogonal Decomposition (SPOD) results provides further insights into the impact of jet actuation on the modification of jet flow structures, thus addressing the effectiveness of the proposed noise control methodology.

Impact of measurement location on direct mitral regurgitation quantification using 4D flow CMR.

Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) shows promise for quantifying mitral regurgitation (MR) by allowing for direct regurgitant volume (RVol) measurement using a plane precisely placed at the MR jet. However, the ideal location of a measurement plane remains unclear. This study aims to systematically examine how varying measurement locations affect RVol quantification and determine the optimal location using the momentum conservation principle of a free jet. Patients diagnosed with MR by transthoracic echocardiography (TTE) and scheduled for CMR were prospectively recruited. Regurgitant jet flow volume (RVoljet) and regurgitant jet flow momentum (RMomjet) were quantified using 4D flow CMR at 7 locations along the jet axis, x. The reference plane (mid-plane, x=0mm) was positioned at the peak velocity of the jet at each cardiac phase, and 3 additional planes were positioned on either side of the jet, each 2.5mm apart. RVoljet was compared to RVolTTE, measured by the proximal isovelocity surface area method and RVolindirect, measured by subtracting aortic forward flow volume from the left ventricle stroke volume derived from 2D phase-contrast at the aortic valve and a stack of short-axis cine CMR techniques. RVoljet and RMomjet were quantified in 45 patients (age 63±13, male 26). In patients with RVoljet at x=0mm ≥ 10ml (n=25), RVoljet consistently increased as the plane moved downstream. RVoljet measured furthest upstream (x=-7.5mm) was significantly lower (39±11%, p<0.001) and RVoljet measured furthest downstream (x=7.5mm) was significantly higher (16±19%, p<0.001) than RVoljet at x=0mm. RMomjet similarly increased from x=-7.5 to 0mm (57±12%, p<0.001) but stabilized from x=0 to 7.5mm (-2±17%). From x=-7.5 to 7.5mm, RVoljet was in consistent moderate agreement with RVolindirect (n=41, bias=-2±24 to 8±32ml, ICC=0.55 to 0.63, p<0.001). The location of a measurement plane significantly influences RVol quantification using the direct 4D flow CMR approach. Based on the converging profile of RMomjet, we propose the peak velocity of the jet as the optimal position.

Two‐Dimensional Jet Flows for Compressible Full Euler System With General Vorticity

ABSTRACTIn this paper, we consider the well‐posedness theory of two‐dimensional compressible subsonic jet flows for steady full Euler system with general vorticity. We show that the stream function formulation for such system admits a variational structure. Then the existence and uniqueness of a smooth subsonic jet flow can be established by the variational method developed by Alt, Caffarelli and Friedman. Furthermore, the far fields behavior of the flow and the existence of a critical upstream pressure are also obtained.

Mitral Anterior Leaflet Perforation Due to Jet Flow in Aortic Valve Insufficiency

Mitral Anterior Leaflet Perforation Due to Jet Flow in Aortic Valve Insufficiency

Flow control of blade-end oscillating jets on corner separation in a high-load compressor cascade

Based on unsteady numerical simulation, the feasibility of utilizing a fluid oscillator to generate oscillating jets for relieving the compressor cascade's corner separation was investigated. First, at design incidence angle, the optimal jet position is located where corner separation is not fully developed (74% axial chord length). Jets at more upstream and downstream positions are less effective due to premature dissipation of jet effects and the occurrence of high corner losses, respectively. The effectiveness of separation control through jet injection increases with higher jet mass flow rates, and the scheme with 0.66% relative jet flow rate exhibits a wide effective jet position range. However, excessively low jet flow rates are sensitive to jet position selection, while excessively high jet flow rates lead to significant mixing losses, resulting in high overall field losses and reduced engineering applicability. Second, the optimal jet scheme remains consistent at both design and high incidence angles and exhibits effective control at other off-design incidence angles. Finally, the oscillating jet suppresses the spanwise development of wall vortex and passage vortex within the blade passage by injecting high-momentum flow. Moreover, proper orthogonal decomposition analysis indicates that the oscillating jet redistributes the modal energy of the original flow field, exciting the vortex structures into high-frequency, small-scale oscillations at the jet frequency. Meanwhile, the oscillating jet primarily facilitates momentum exchange through strong mixing with passage vortex, wall vortex, and concentrated separation vortex, ultimately mitigating corner separation and reducing corner loss.

Interpretation and prediction of the three-dimensional coherent structure and its dynamics of tornado-like vortex via delayed proper orthogonal decomposition

This study proposes a three-dimensional mode-based surrogate framework to predict the tornado-like vortex (TLV) derived from the fuzzy neural network and delayed proper orthogonal decomposition method. First, near-break-down TLV is simulated via large-eddy simulation, and its mean, fluctuating and statistical flow feature is analyzed. Then, three-dimensional spatiotemporal features of coherent structure are extracted and interpreted. Next, the capability of the proposed framework to predict the future state of an unsteady chaotic TLV flow field is systematically evaluated, including the spatiotemporal variation of velocity, pressure, and vorticities as well as flow statistics. Finally, parametric analysis is also conducted to investigate the influence of three key parameters [i.e., Fuzzy rules of the state network or output network (K1 or K2), time delayed embedding number (d)] contained in the framework and the step number of forward prediction (K) on the predicted accuracy. Results show that for near-break-down TLV, vortex wandering effect largely affects its dynamical feature, and its three-dimensional characteristics are distinct, exhibiting the essence of the swirling jet flow. 3D mode-based surrogate model can correctly predict the tornado-like vortex with a relative error of less than 2% for the radial, tangential, and vertical velocity component. It is found that fuzzy rules and time-delayed embedding number has great effect on prediction accuracy. Thus, to achieve optimal predicting effect, it is suggested that d is taken as 8, K1, and K2 are taken as 18, and when making multi-step predictions, the largest K should not exceed 7.

Investigation on drawdown dispersion process of light floating particles in a pilot scale jet flow high shear mixer

Investigation on drawdown dispersion process of light floating particles in a pilot scale jet flow high shear mixer

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&amp;deg;, 52.5&amp;deg;, and 60&amp;deg;. 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 &amp;#177; 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&amp;deg; and the aperture H/D &amp;#61; 1.

Study on pilot-scale inline jet flow high shear mixer: Discharge, macro-mixing time, and residence time distribution

Study on pilot-scale inline jet flow high shear mixer: Discharge, macro-mixing time, and residence time distribution

ENHANCING HEAT TRANSFER IN CHANNEL FLOW USING SYNTHETIC JETS

Synthetic jet's effectiveness in flow control, fluid mixing enhancement, and cooling has been established. The current study aims to examine the improvement of fluid blending and heat dissipation rate of two water inlets with varying temperatures in a channel that is disturbed by a synthetic jet at different excitation frequencies. The simulation analysis predicts the temperature distributions and the fully develop the velocity profile along symmetrical plane of the channel with interference of synthetic jet using establish CFD software. The RNG k- ε turbulence model was employed to compute the turbulent flow produced by the synthetic jet. A moving mesh approach was employed to replicate the movement of a synthetic jet diaphragm. The results indicate that the fluid flow behavior in the channel disrupted by the synthetic jet flow. Hence, indicating to an enhance in both the fluid flow velocity and the heat transfer rate. A higher frequency of the actuator enhances fluid mixing and reduces the channel distance required to achieve temperature equilibrium within the channel in comparison to a lower frequency of the actuator.

A Parameterized Prediction Method for Turbulent Jet Noise based on Physics-informed Neural Networks

Abstract Turbulent noise prediction is integral to fluid equipment design, and multiple simulations or experiments are often required for noise distribution under varying operating conditions during the design optimization process, which could be expensive. Recently, the Physics Informed Neural Networks (PINNs) method has emerged as an efficient machine learning method for solving parameterized partial differential equations with geometric shapes, boundary conditions, and equation parameters as variable parameters through a single training session without data. In this study, a parameterized prediction method is developed to predict turbulent jet noise based on PINNs without any training datasets. Both two-dimensional (2D) and three-dimensional (3D) jet flow problems are solved. The 2D problem is solved with the Reynolds number as a variable parameter, and the 3D problem is solved with the Reynolds number and nozzle eccentricity as variable parameters. The predicted results are in good agreement with those from conventional computational fluid dynamics (CFD), with average errors of 3% and 6% for the 2D and 3D flow and acoustic power fields, respectively. In terms of computational efficiency, the time required by the method for the three-dimensional problem with two variable parameters is only one-seventh of that of the traditional CFD method. This study demonstrates that for engineering noise scenarios with varying parameters, the method based on PINNs offers a more efficient parameterized predicting approach and is promising for future applications.

Cosmic ray contributions from rapidly rotating stellar mass black holes: cosmic Ray GeV to EeV proton and anti-proton sources

In Radio Super Novae (RSNe) a magnetic field of (B × r) = 1016.0±0.12 Gauss × cm is observed; these are the same numbers for Blue Super Giant (BSG) star explosions as for Red Super Giant (RSG) star explosions, despite their very different wind properties. The EHT data for M87 as well for low power radio galaxies all show consistency with just this value of the quantity (B × r), key for angular momentum and energy transport, and can be derived from the radio jet data. We interpret this as a property of the near surroundings of a black hole (BH) at near maximal rotation, independent of BH mass. In the commonly used green onion model, in which a 2 π flow changes over to a jet flow we interpret this as a wind emanating from the BH/accretion disk system and its surroundings. Near the BH collisions in the wind can produce a large fraction of anti-protons. In this scenario the cosmic Ray (CR) population from the wind/jet is proposed to be visible as EeV protons and anti-protons in the CR data to EeV energy, with a E−7/3 spectrum. This can be connected to a concept of inner and outer Penrose zones in the ergo-region. The observed numbers for the magnetic field imply the Planck time as the governing time scale: A BH rotating near maximum can accept a proton per log bin of energy in an extended spectrum with the associated pions every Planck time.

THE USE OF FLOW MIXERS IN OXIDIZED BITUMEN PRODUCTION

In the process of road bitumen production, the raw material mixture is fed into an oxidizing column, where it is oxidized with air oxygen. Using this production method, a large amount of oxygen, without reacting, is sent to the scrubber and then to the afterburning furnace. One of the ways to use air oxygen more efficiently in the process of oxidized bitumen production is the use of pre-oxidant mixers. There is also a problem related to such a quality indicator as bitumen aging due to the use of air for mixing commercial bitumen, this problem is solved in a similar way – using a flow jet hydraulic mixer with a cone swirl. This article compares the existing remote gas-liquid cavitation vortex apparatus with a flow jet hydraulic mixer based on building their models in the Ansys CFX program and determining the air concentration in the mixture passing through the mixer. This indicator will reveal the most effective apparatus for the preoxidation of raw materials for bitumen production. A simulation of the flow of tar through a flow jet hydraulic mixer with a conical flow swirl is also performed to determine the turbulence and turbolization of the flow, which shows its effectiveness in mixing compounded bitumen.

One-dimensional temperature measurement of supersonic jet flow by resonantly ionized photoemission thermometry of molecular nitrogen

As the field of fluid dynamics progresses, the demand for sophisticated diagnostic methods to accurately assess flow conditions rises. In this work, resonantly ionized photoemission thermometry (RIPT) has been used to directly target and ionize diatomic nitrogen (N2) to measure one-dimensional (1D) temperature profiles in a supersonic jet flow. This technique can be considered non-intrusive as the premise uses resonantly enhanced multiphoton ionization (REMPI) to target molecular nitrogen. This resonance excites N2 into absorption bands of the P, Q, and R rotational branches of N2 (b1Π u ). The ideal (3 + 1) REMPI scheme excites from the ground state and ionizes N2 (b1Π u ←X1Σ g +) where de-excitation results in photoemission from the first negative band of ionized N2+(B2Σu+→X2Σ g +) as nitrogen returns to the ground state. The resulting emission can be observed using an intensified camera, thus permitting inference of the rotational temperature of ground-state molecular nitrogen. A linearly regressive Boltzmann distribution is applied based on previous calibration data for this technique to quantify the temperature along the ionized line. This work applies this technique to a pure N2 supersonic jet in cross-flow and counter-flow orientations to demonstrate N2 RIPT’s applications in a supersonic flow. Temperature variations are observed at different locations downstream of the exit in cross-flow, and axisymmetric in counter-flow, to generate profiles characterizing the flow dynamics. Due to the collisional effects resulting from the number density of N2 at higher pressures, a (3 + 2) REMPI scheme is observed throughout this text.

Volumetric supraglottal jet flow field analysis in synthetic multilayered self-oscillating vocal fold model

Volumetric supraglottal jet flow field analysis in synthetic multilayered self-oscillating vocal fold model

Axisymmetric cavity noise control using passive protrusion

This paper introduces a passive protrusions to reduce undesirable structural loading and high-amplitude noise radiation in axisymmetric cavities, are common in industries, including pipelines and aerospace. A comprehensive experimental investigation of the pipe-cavity noise control system is conducted, exploring various protrusion locations and lengths at different Nozzle Pressure Ratios (NPRs). The study examines protrusions placed at the leading, trailing, and both leading and trailing edges of the axisymmetric cavity. Additionally, detailed experiments are performed to analyze the impact of protrusion lengths on unsteady cavity pressure and far-field noise radiation. Cavity pressure fluctuations and far-field noise levels are measured for both cases: with and without protrusions in the pipe-cavity setup. The Proper Orthogonal Decomposition (POD) technique is applied to the time-resolved Schlieren images to show the effect of passive protrusions on the exit jet flow structure. Results demonstrate that a protrusion located at the trailing edge yields superior noise reduction compared to other configurations. The efficacy of this protrusion in mitigating cavity noise is attributed to its ability to efficiently alleviate the feedback mechanism responsible for cavity noise generation and break down the recirculation region within the cavity system. Significant noise reduction, approximately 4 dB, is achieved at lower NPRs, and substantial noise reductions are also observed for the underexpanded jet condition.

Spontaneous snapping-induced jet flows for fast, maneuverable surface and underwater soft flapping swimmer.

Manta rays use wing-like pectoral fins for intriguing oscillatory swimming. It provides rich inspiration for designing potentially fast, efficient, and maneuverable soft swimming robots, which, however, have yet to be realized. It remains a grand challenge to combine fast speed, high efficiency, and high maneuverability in a single soft swimmer while using simple actuation and control. Here, we report leveraging spontaneous snapping stroke in the monostable flapping wing of a manta-like soft swimmer to address the challenge. The monostable wing is pneumatically actuated to instantaneously snap through to stroke down, and upon deflation, it will spontaneously stroke up by snapping back to its initial state, driven by elastic restoring force, without consuming additional energy. This largely simplifies designs, actuation, and control for achieving a record-high speed of 6.8 body length per second, high energy efficiency, and high maneuverability and collision resilience in navigating through underwater unstructured environments with obstacles by simply tuning single-input actuation frequencies.

Effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets

The effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets was experimentally investigated in this study. A single jet from a pair of dual jets was pulsed by a loudspeaker. The flow evolution processes were examined using the laser-light sheet-assisted smoke flow visualization method. The visual spread of the jet flow was measured using the binary boundary edge detection technique. A hotwire anemometer was used to detect the instantaneous velocities, mean velocities, turbulence intensities, Lagrangian integral time, and length scales. The dispersion capabilities of the jet fluid were evaluated employing the tracer-gas concentration detection technique. Two characteristic flow modes, namely the coherent vortices and vortex breakup, could be classified based on pulsation intensity. At Ip < 1.0, the flow was characterized by coherent vortices, which maintained coherence within one excitation cycle. At Ip > 1.0, vortex breakup occurred, where vortices deformed, lost coherence, and transformed into puff-shaped vortical structures within one excitation cycle. The vortices emerging from the pulsed jet undergo deformation, evolving into puff-shaped vortices, and subsequently fragment into smaller turbulent eddies more quickly than the synchronized vortices from the non-pulsed jet. This leads to significant penetration and velocity fluctuations in the trajectory of the pulsed jet. Consequently, the overall spread width and concentration reduction index of the single-pulsed dual parallel plane jets exceed those of the non-pulsed dual parallel plane jets.

CFD Investigation of Mechanical Heart Valve Orientations in Modulating Left Ventricular Hemodynamics

This study provides a comprehensive computational analysis of how mechanical heart valve orientations impact left ventricular (LV) hemodynamics, with potential implications for surgical valve placement. Focusing on monoleaflet valves (MLV) and bileaflet valves (BLV), the research explores how different valve angles influence blood flow patterns within the LV chamber. The analysis includes velocity contours, streamline patterns, vorticity contours, and temporal velocity fluctuations to elucidate the effects of valve orientation on LV performance. Findings indicate that valve orientation significantly influences flow coherence and blood velocity. For instance, a 20-degree orientation in the MLV alters jet flow in ways that could affect wall shear stress distribution. At a 45-degree angle, the MLV produces a more centralized jet flow, enhancing flow uniformity and aligning more closely with physiological conditions. In contrast, a 55-degree angle skews the jet flow, potentially leading to adverse hemodynamic effects. Similarly, BLV orientations at 45, 55, 60, and 70 degrees showed that lower angles improved flow efficiency, reducing energy losses and minimizing the risk of regurgitation, while higher angles led to turbulent and potentially damaging flow patterns. Comparative results at a 45-degree orientation demonstrated the superior performance of BLV in regulating normal velocity, with BLV reducing average blood velocity by 38.77% compared to a 29.53% reduction with MLV. These results underscore the importance of optimizing mechanical heart valve orientations to enhance left ventricular hemodynamics. The findings carry significant clinical implications, supporting evidence-based valve placement decisions that can substantially improve patient outcomes, survival rates and long-term cardiovascular health.

Flow analysis of steady state forward flow of aortic valve prostheses using Particle Image Velocimetry

Abstract Transcatheter aortic valve replacement (TAVR) has become the standard therapy for aortic valve stenosis in patients with high surgical risk. Understanding the flow dynamics in TAVR is crucial for its evaluation and optimization. Experimental flow measurement by means of Particle Image Velocimetry (PIV) is increasingly applied alongside numerical analyses. This study introduces a novel test rig concept enabling the determination of velocity fields using Stereo-PIV under steady forward flow conditions through a TAVR during the peak systole matching the ISO 5840-1:2021 requirements. The experimental setup utilized an impeller pump to generate steady forward flow through a silicone aortic root model with implanted TAVR. A Stereo-PIV setup captured velocity fields in both ventricular inflow and aortic outflow regions. Test conditions were based on physiological flow rates determined from pulsatile measurements. Illumination of the added particles in the test fluid was achieved using an Nd:YAG laser. Fluorescent polystyrol particles (size: 50 μm) were used for flow visualization. Results showed characteristic flow patterns: a central jet flow entering the TAVR in the ventricular flow field. A jet flow directed towards the sinus side and a recirculation zone forming on the opposite side of the sinus could be detected in the aortic outflow. The width of the recirculation zone increases with distance from the TAVR. Maximum flow velocities were detected at 0.78 m/s for the ventricular flow field and 0.94 m/s for the aortic flow field. This study provides a comprehensive approach for fluid dynamic analysis of TAVR under steady flow conditions, offering insights into flow mechanics performance crucial for device optimization. Further investigations could enhance the PIV - measurement procedure by increasing both the spatial resolution and the tracer particle density within the acquired images for a comprehensive characterization of TAVR flow dynamics.