Circular Jet Flow Research Articles

Trajectory and spreading of falling circular dense jets in shallow stagnant ambient water

This study investigates the trajectory and spreading of a horizontal circular dense jet flow discharged above the water surface, the flow of which falls into shallow stagnant ambient water. For this purpose, 27 experiments were performed using three diameters, flow rates, and falling heights to investigate jet trajectory. In addition, nine experiments with constant falling height were conducted to study jet spreading. The densimetric Froude number of the jet flow at the nozzle outlet and water surface of the present study ranged from 0.72 to 4.22 and 36.96 to 86.10, respectively. The data pertaining to this study were extracted and analyzed through image processing. The results of the experiments showed that by increasing both the momentum and falling height, the trajectory of the jet flow reached a farther distance from the discharge nozzle. The spreading of the outer boundaries of the dense circular falling jet flow tended to extend downstream of the impact point and had an elliptical motion on the bed. The relationship between radial distance from the impingement point to the outer boundary of flow and time was determined to have a power of 0.67 for flow along the flume and 0.59 for flow along the flume's width.

A novel compartmental approach for modeling stomach motility and gastric emptying

The stomach, a central organ in the Gastrointestinal (GI) tract, regulates the processing of ingested food through gastric motility and emptying. Understanding the stomach function is crucial for treating gastric disorders. Experimental studies in this field often face difficulties due to limitations and invasiveness of available techniques and ethical concerns. To counter this, researchers resort to computational and numerical methods. However, existing computational studies often isolate one aspect of the stomach function while neglecting the rest and employ computationally expensive methods. This paper proposes a novel cost-efficient multi-compartmental model, offering a comprehensive insight into gastric function at an organ level, thus presenting a promising alternative.The proposed approach divides the spatial geometry of the stomach into four compartments: Proximal/Middle/Terminal antrum and Pyloric sphincter. Each compartment is characterized by a set of ordinary differential equations (ODEs) with respect to time to characterize the stomach function. Electrophysiology is represented by simplified equations reflecting the “slow wave behavior” of Interstitial Cells of Cajal (ICC) and Smooth Muscle Cells (SMC) in the stomach wall. An electro-mechanical coupling model translates SMC “slow waves” into smooth muscle contractions. Muscle contractions induce peristalsis, affecting gastric fluid flow velocity and subsequent emptying when the pyloric sphincter is open. Contraction of the pyloric sphincter initiates a retrograde flow jet at the terminal antrum, modeled by a circular liquid jet flow equation.The results from the proposed model for a healthy human stomach were compared with experimental and computational studies on electrophysiology, muscle tissue mechanics, and fluid behavior during gastric emptying. These findings revealed that each “ICC” slow wave corresponded to a muscle contraction due to electro-mechanical coupling behavior. The rate of gastric emptying and mixing efficiency decreased with increasing viscosity of gastric liquid but remained relatively unchanged with gastric liquid density variations. Utilizing different ODE solvers in MATLAB, the model was solved, with ode15s demonstrating the fastest computation time, simulating 180 s of real-time stomach response in just 2.7 s. This multi-compartmental model signifies a promising advancement in understanding gastric function, providing a cost-effective and comprehensive approach to study complex interactions within the stomach and test innovative therapies like neuromodulation for treating gastric disorders.

Experimental investigation of heat transfer effects in impinging circular jets confined by inclined plates

In this study, the effects of heat transfer in turbulent flow fields of impinging circular jet confined by inclined plates were investigated experimentally. Temperature distributions on the impingement plates were acquired with thermal camera. Temperature measurements were carried out on the impingement plate in four different impinging circular jet flow setups confined by plates with inclination angles of θ = 0°, 15°, 30° and 45°, with an inter-plate spacing of 0.5 ≤ H/D ≤ 10 and a Reynolds number range of 20,000 ≤ Re ≤ 30,000. The effects of confinement plate inclination angle, intervals among plates and Reynolds number on the Nusselt distributions of the impingement plates were examined. It was found that Nusselt values on the impingement plate increase with increasing Reynolds number and decrease with increasing intervals among plates. Secondary top points become visible in the Nusselt distributions on the impingement plate at H/D ≤ 3 values of the inter-plate spacing. The position of the secondary top points on the impingement plate move towards the ends of the impingement plate with increasing inclination angle of confinement plate.

Fast and accurate flow measurement through dual-camera light field particle image velocimetry and ordered-subset algorithm

Light field particle image velocimetry (LF-PIV) can measure the three-dimensional (3D) flow field via a single perspective and hence is very attractive for applications with limited optical access. However, the flow velocity measurement via single-camera LF-PIV shows poor accuracy in the depth direction due to the particle reconstruction elongation effect. This study proposes a solution based on a dual-camera LF-PIV system along with an ordered-subset simultaneous algebraic reconstruction technique (OS-SART). The proposed system improves the spatial resolution in the depth direction and reduces the reconstruction elongation. The OS-SART also reduces the computational time brought by the dual-camera LF-PIV. Numerical reconstructions of the particle fields and Gaussian ring vortex field are first performed to evaluate the reconstruction accuracy and efficiency of the proposed system. Experiments on a circular jet flow are conducted to further validate the velocity measurement accuracy. Results indicate that the particle reconstruction elongation is reduced more than 10 times compared to the single-camera LF-PIV and the reconstruction efficiency is improved at least twice compared to the conventional SART. The accuracy is improved significantly for the ring vortex and 3D jet flow fields compared to the single-camera system. It is therefore demonstrated that the proposed system is capable of measuring the 3D flow field fast and accurately.

Jet flow control by synchronous drive of two DBD-PAs in nozzle and on bluff body

In this study, two dielectric barrier discharge plasma actuators (DBD-PAs) are driven at different times to control a circular jet flow. DBD-PA was installed inside a nozzle and on a disk-shaped bluff body above the nozzle. A vortex was generated in the jet using DBD-PA in the nozzle, and the development of the vortex was controlled using the DBD-PA installed in the disk-shaped bluff body above the nozzle. The two DBD-PAs were driven with a time lag based on the time the vortex reached the bluff body. The findings reveal that the vortices did not pair with each other when the DBD-PA of the bluff body was slightly delayed from the timing of the occurrence of the vortex on the circulating flow side. When the vortices did not pair, the flow was not entrained in the circulating flow, causing the jet width to widen. The vortices paired with each other when the DBD-PA of the bluff body was driven at the same time as or long after the occurrence of the vortex on the circulating flow side. When the vortex pair with each other, they collapse quickly after pairing, and the jet width narrows, as the flow is entrained in the circulating flow. The difference in jet width downstream of the bluff body was found by driving the two DBD-PAs installed inside the nozzle and on the bluff body at different times.

Chaotic Advection of a Passive Admixture in a Circular Barotropic Jet Flow

Chaotic Advection of a Passive Admixture in a Circular Barotropic Jet Flow

Experimental study of vortex formation in pulsating jet flow by time-resolved particle image velocimetry

We experimentally investigate the pulsating circular jet flow at moderate Reynolds numbers. By applying time-resolved particle image velocimetry in the axial-radial plane, we measure the near-field velocity fields with the jet source temporally modulated by sinusoidal pulsations. As a baseline, the steady jet flow with the same mean Reynolds number is tested. The direct comparisons of the mean and fluctuating velocity fields show that the whole potential core as well as the axisymmetric shear layer is modulated by the pulsation effect. Meanwhile, larger-scale vortices are formed in the shear layer with phase correlation of the pulsation cycle. As a result, the pulsation increases the turbulent mixing in the latter half of the potential core, and it extends the fluid entrainment further in the radial direction. The increased fluid entrainment of the ambient quiescent fluid is clearly identified by the attracting Lagrangian coherent structures as the bounds of the growing vortices within the shear layer. By analyzing the dynamic modes, we find that the low-frequency off-the-axis helical structures, which are dominant in the steady jet flow, are inhibited. The axisymmetric jet column mode and its harmonics along the axis are strengthened by the pulsation effect. Furthermore, the vortex formation mainly takes place particularly in the deceleration phase, whereas a shock-like wave front is formed during the acceleration, indicating the distinct roles of the pulsation phases in the jet instability.

Mean velocity equation for fluctuating flow

Arguments are presented that the momentum equation derived by Zwanzig–Mori technique of N-particle statistical mechanics is identical to the Reynolds equation for the mean velocity field in fluctuating hydrodynamics; thus, calculating the non-linear stress of the momentum equation is perhaps a means to avoid the closure problem of turbulence theory. In this paper, the third-order term of the friction force is calculated. Multilinear mode coupling theory is applied in order to obtain formulas for the third- and fourth-order equilibrium time correlation functions appearing in the expression. The force term is obtained as a multilinear convolution integral containing higher order gradients of the velocity field.As an application, circular jet flow for low Reynolds numbers is investigated. Numerical solutions have been obtained from an iteration starting with the corresponding solution of the Navier–Stokes equation. Deviations become distinct for Re>30.

Prediction of Inner Grooved Circular Jet Flow with Artificial Neural Networks

Prediction of Inner Grooved Circular Jet Flow with Artificial Neural Networks

Coaxial Circular Jet Flows with Conical Attachments

This study is devoted to experiments on jet ows, which have many application areas. It shows the obtained jet ow structure. The experiments were carried out in a subsonic sucking wind tunnel having cross-section of 32 × 32 cm, length of 75 cm, and turbulence densities of 0.5%. One-channel hot-wire anemometer (HWA) was used in measurements. For circular jet, a steel pipe was used with a length of 120 cm and a diameter of 8 mm. Air generator was used for generating air into the jet ow and measurements were done at di erent jet ow velocities. Moreover, a conical di user with a length of 21 cm and 6◦ slope was attached to the nozzle exit and e ect of this di user on jet ow was examined. Seven types of measurement in three di erent categories were carried out. In experimental studies, velocity and turbulence distribution, axial velocity variation, jet half widths and, using these, jet di usion rates and angles were measured. Moreover, ow analyses were done by drawing moment and frequency distribution for measurement sensitivity. These experimental results were compared with the studies on jet ow.

Investigation of Grooved Circular Jet Flow Experimentally and Using Computational Fluid Dynamics

Investigation of Grooved Circular Jet Flow Experimentally and Using Computational Fluid Dynamics

Elliptic jet control with cross-wire

The effect of cross-wire on the aerodynamic mixing of circular and elliptic sonic jet flow fields is studied experimentally in the presence of favourable pressure gradient at the orifice exit. The cross-wire is found to reduce the amplitude of pitot pressure oscillation drastically, and thus weakens the shock cell structure in the jet core. In the case of elliptic jets, the effectiveness of cross-wire is found to be dependent on its location at the orifice exit. For lower aspect ratio jets (AR 2), cross-wire along the major axis proves to be more effective in enhancing mixing, but as the aspect ratio increases to higher values (AR 6), cross-wire along the minor axis becomes more effective in promoting the jet mixing. The pressure profile results indicate that the cross-wire located on the major axis advances the axis-switching phenomenon, while the cross-wire along the minor axis shifts the axis-switching location further downstream compared to uncontrolled jet. The jet bifurcation caused by the cross-wire has been captured in the shadowgraph pictures.

On the three-dimensional precessing jet flow past a sudden expansion

A circular jet flow past an abrupt expansion under some conditions switches intermittently between two states: quasi-axisymmetric expansion and gyroscopic-like precessing motion. In this work, an experimental investigation into the self-excited precessing flow generated by a 5:1 expansion of a round jet in a coaxial cylindrical chamber is carried out by means of tomographic particle image velocimetry. The experiments are performed on a jet issued from a short pipe at a Reynolds number equal to 150,000. Proper orthogonal decomposition (POD) is applied to extract information on the organization of the large coherent structures of the precessing motion. The application of this technique highlights the dominance of three modes: the most energetic two are associated with the jet precession; the third one is representative of the axial motion. An estimate of the precession probability based on the modal energy obtained from the application of POD is proposed. The precession frequency is extracted using a low-order reconstruction (LOR) of a subset of the POD modes. The reconstructed flow field topology obtained by the LOR highlights an underlying mechanism of swirl generation in proximity of the inlet nozzle; the phenomenon is closely related to the interaction between the entrainment in the far field and the recirculation regions in the near field. The application of a stability criterion shows that the self-induced swirl flow results to be unstable. The instability is responsible for the generation of helicalshaped vortices in the near field, even though the dominant feature for the unconfined jet issued from the same nozzle is the axisymmetric ring-vortices generation.

Experimental Research on the Attenuation Rules of Personalized Air-Conditioning Nozzle Jet Flow in Aircraft Cabins

A full size simulation laboratory aircraft cabin comprising three rows of seats has been built. This represents the Airbus A320 and the China C919 aircraft. Experimental research on the attenuation rule of the individual air-conditioning isothermal jet flow from nozzles positioned above the seats was conducted. The results show that axial air velocity continuously decreases with increasing cross-sectional distance. For a distance x < 0.4 m, (the axis air velocity sharp attenuation area), the velocity of attenuation slows. When 0.7 m x < 0.9 m, the velocity remains at about 1m.s-1 with the vents fully open, and at about 0.5 m.s-1 with the vents half open. The air velocity distribution of different cross-sections is axisymmetric and basically in line with the circular outlet jet flow rule. Combined with empirical formulae, the turbulent coefficient values of the isothermal jet flow in the airplane cabin was established as 0.1021 with the vents fully open and 0.1776 with the vents half open. The spread angles α of jet flow for these two conditions were found to be 19.14° and 31.12° respectively. The axial velocity attenuation rule was also confirmed. The experimental results align with those anticipated by calculation.

Simulation of a Nozzle‐Jet Configuration Including the Acoustic Near‐Field

AbstractA numerical simulation setup is presented which allows to study a circular jet flow configuration in which the nozzle is included in the simulation domain. Direct Numerical Simulations (DNS) are performed using up to 10th order compact finite‐difference schemes which are stabilized by applying a mild low‐pass filter. A parallelization approach has been implemented which shows good weak and strong scaling behavior. At the inflow the Synthetic Eddy Method is employed to generate turbulent fluctuations in the nozzle boundary layer with prescribed statistics, which are imposed by a sponge (forcing) layer technique. Simulation results for the jet flow field obtained at Reynolds number ReD = 19000 and a Mach number Ma = 0.9 as well as for the acoustic near‐field are found to be in good agreement with recent nozzle‐jet simulation results as well as experimental findings. (© 2012 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Wind power of small wind turbines in turbulent open jets

Open jet wind tunnel testing provides an alternative solution to expensive online wind power measurements for researchers and small wind turbine developers. However, there is a lack of knowledge for high Reynolds number and large diameter jet flows. In this paper, the structure of circular open jet flows is reviewed. Theories and experimental correlations are combined to extend our understanding of fully developed turbulent jets. Analytical relations are derived to calculate the correct wind power of the jets. The corresponding reduction in power generated by small wind turbines is explained. The effects of various parameters on the power production of a small wind turbine, such as the jet diameter, the distance of the wind turbine from the jet nozzle and the wind turbine hub diameter, are investigated and the results are discussed.

Effects of notch geometry and sharpness on turbulent jets issuing from indeterminate-origin notched nozzles

An experimental investigation using hot-wire anemometry to identify the effects of notch configuration and relative sharpness on notched indeterminate-origin turbulent jets at R e = 20,500 was carried out. The notches are characterized by their V- and A-shaped cuts, as well as their relative sharpness due to the design aspect ratio ( A R = 2 and 4) of the notch. Regardless of exact notch geometry, high aspect-ratio nozzles are shown to produce significant flow differences between measurements taken along peak and trough planes, in contrast to low aspect-ratio nozzles. Half-jet width results demonstrate that as the aspect-ratio increases, smooth peaks result in a constant increase within the measurement range while sharp peaks produce an initial decrease till some downstream location before increasing thereafter. In contrast, smooth and sharp trough produces significant nonlinear increases in the half-jet widths with the aspect-ratio increment. Cross-over points linked to axis-switching behaviour are observed for all nozzles except A R = 4 A-notched nozzle, when half-jet widths along peak and trough planes for each nozzle are compared. Increasing the aspect ratio also results in a 50% reduction in the distance away from the nozzle origin where the cross-over point occurs for V-notched nozzles. On the other hand, similar increase in the aspect ratio produces no cross-over point for A-notched nozzles. These results indicate that suitably configured notched nozzles are able to impart significant control over circular jet flow behaviour by inducing and manipulating axis-switching behaviour typically found in noncircular jets.

Visualization of circular subsonic jet flow by DNS

Visualization of circular subsonic jet flow by DNS

Nose Blowing for Side Force Control on Slender Cones at High Incidence

Vortex asymmetry on axisymmetric pointed forebodies at high angles of incidence results in side forces and adverse yawing moments even in symmetric flight. An experimental investigation has been carried out at low speeds to study the effectiveness of axial nose blowing against the oncoming flow for side force control on two slender cones. Tests were made on the 8 and 12 deg cone models with (circular)jet flow over a Reynolds number range of $0.4\times10^6$ to $5.4\times10^6$. Jet-to-freestream velocity ratio was varied up to 2.0, and the blowing diameter was varied as well. Force measurements were carried over the incidence range of 0 to 45 deg, and limited surface pressure distributions were obtained on the 12 deg cone model. The results explicitly show the effectiveness of nose blowing for side force control over a wide range of Reynolds numbers, and minimum side force was reached around a jet velocity ratio of 1.0. An important result is that the side force reduction correlates with jet velocity ratio in the range of parameters studied. Broad similarities in the trend of side force reduction with the nose blowing and the nose bluntness suggest that the interaction of axial jet with freestream flow results, possibly, in what we may call fluid dynamic blunting.

Experimental investigation on mixing enhancement mechanism of turbulent jet flow with tabbed nozzle

Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generated by the tabs of different sizes and numbers were observed from the flow visualization images. Combined with flow visualization, hot-wire measurement gave a quantitative insight of the effect of various tabbed jet flows. Instantaneous two-component velocity signals (longitudinal and transverse velocity components) at different cross sections along radius direction and streamwise direction with different tabbed jet nozzles were measured using hot-wire anemometer. Average flow field parameters of tabbed jet flow such as mean velocity, turbulence intensity, vorticity were analyzed and the effects of tabs with different sizes and numbers were compared with that of circular no-tab jet flow. It is revealed that the generation of a series of counter-rotating quasi-streamwise vortices, azimuthal vortices and double-row azi-muthal vortex are the reasons for mixing enhancement of tabbed turbulent jet flow.