Incompressible Turbulent Jet Research Articles

An adaptive mesh refinement approach based on optimal sparse sensing

We introduce a new approach for adaptive mesh refinement in which adaptivity is driven by low rank decomposition and optimal sensing of the dynamically evolving flow field. This method seeks an ordered set of locations for mesh adaptation from the instantaneous data-driven basis of an online proper orthogonal decomposition of the velocity, which organizes features into sparse optimal orthogonal modes based on an energy norm. The sensing is achieved via a computationally expedient discrete empirical interpolation method using rank-revealing QR factorization (Drmac and Gugercin SIAM J Sci Comput 38(2):A631–A648, 2016). The methodology is applicable to a wide range of numerical discretizations, and is tested on a spatiotemporally evolving incompressible turbulent jet, a complex wind turbine wake, and supersonic flow over a forward-facing step. The proposed approach is demonstrated to predict accurate velocity statistics and yield significantly smaller grids in comparison to gradient-based methods. The algorithm is seen to focus refinement in the vicinity of dynamically significant regions such as those characterized by high turbulence kinetic energy, coherent structures and shock interactions. Moreover, the approach does not require parameters or thresholds, which may be difficult to obtain for complex flows, to be known a priori to facilitate mesh adaptation.

Robust and accurate open boundary conditions for incompressible turbulent jets and plumes

We show that a popular convective open boundary condition (OBC) is unsuitable in the direct simulation of incompressible turbulent jets and plumes, because (1) the boundary condition modifies their spreading rate; (2) the results are domain dependent; and (3) the boundary condition is liable to cause instability and therefore requires domains that are much larger than the area of interest. We demonstrate the accuracy of new axisymmetric OBCs compared to the standard OBC by conducting direct numerical simulation (DNS) of a turbulent plume and a turbulent jet. The new OBCs conform to the fundamental features of statistically axisymmetric turbulent flows, regardless of the computational domains on which they are imposed. They do not contain tunable parameters and are dynamical, accounting for the strength and extent of a flow at a given time, which eliminates the need for calibration to particular cases. The implementation presented herein is computationally efficient and robust in the vicinity of turbulent flows.

An experimental examination of an impulsively started incompressible turbulent jet

The transient morphology and entrained fluid distribution of an impulsively started turbulent jet are studied in an experiment that examines a jet of dyed water injected into a large water reservoir. The images obtained, using a video recorder, are processed to determine the time-dependent length, tip velocity, and volume of the jet. Abel inversion is used in conjunction with digital images to examine the transient distribution of the ambient fluid entrained into the jet. Results from the analysis also describe the self-similarity of the jet’s flow and entrainment.

Dynamics and Control of Coherent Structure in Turbulent Jets

Current understanding of coherent structure dynamics in incompressible turbulent jets as explained by the nonlinear stability theory is reviewed, focusing on nonswirling turbulent jets. Topics addressed include hydrodynamic stability theory and coherent structures; dynamics of energy transfers among different scales of motion; nonlinear development of amplitude; development of single-frequency coherent mode; fundamental-subharmonic interaction and vortex pairing; and reversal of Reynolds stresses. Attention is also given to the effect of initial phase-difference angle between fundamental and subharmonic, conditions for resonance interaction, modulation of spreading rate by controlling coherent structure, turbulence enhancement or suppression due to excitation, 3D effects, jet noise, and swirling jets.

Prediction of a Three-Dimensional Circular Turbulent Jet in Crossflow

A quasi-three-di mensional integral method is used to solve the problem of the isothermal incompressible turbulent jet. The jet is submerged and is circular at its origin. The mathematical model is based on two integral momentum equations, one written for a direction parallel to the jet centerline and the other for a direction perpendicular to the centerline. For their solution, the entrainment rate into the jet is determined as the linear combination of a modified straight jet entrainment and the entrainment into a vortex pair. The family of velocity profiles required for the integration of the momentum equations is three-dimensional. The profiles are determined along the jet centerline on the basis of the distorted jet cross sections, thus being nonsimilar. The mathematical model is numerically solved, yielding the internal jet flowfield. Results are compared to experiments with different injection velocity to crossflow velocity ratios and with different injection angles. Agreement between theory and experiment is found to be satisfactory in some cases and good in others.

有限長側壁への噴流付着現象

A two-dimensional incompressible turbulent jet issuing nearly parallel to a side-wall of finite length develops the pattern of either a reattaching flow or a separated flow. When the side-wall is long enough, the jet reattaches naturally to the wall. The jet is thought to be unstable and separate, if the wall is considerably short. In the present paper, an analytical model is discussed. The calculated results for steady phenomena of a wall-reattaching jet show good agreement with experiments. Experimental observations showed even if the wall length is shorter than the offset distance, the separated jet can be forced to reattach to the side-wall by an instantaneous control flow and be kept stable. Therefore, from the viewpoint of controlling flow direction or flow state, three regions along the wall, length are defined as follows: (I) Natural reattaching region-when the side-wall is long enough, the jet reattaches naturally to the wall. (II) Bistable region-in a certain section of the wall length, both the separated flow and the forced reattaching flow are possible, either of which is selectively chosen by a control flow and kept stable. (III) Separated region-the jet never reattaches, if the wall is very short. These three regions are distinctively divided by two lines; a natural reattachment limit line and a forced reattachment limit one. It was confirmed that Reynolds number has no influence either on the overall flow pattern, or on the detailed construction of the flow.

An Experimental Study on Confluence of Two Two-Dimensional Jets

An experimental study on the confluence of two two-dimensional incompressible turbulent jets, issuing from nozzles with angle θ0 against the nozzle exit plane, has been presented. The axial momentum and the energy flux of the jets along the z-axis perpendicular to the exit plane are calculated by using the measured values of velocity and pressure distributions. It has been shown that the axial momentum flux along the z-axis decreases owing to the confluence, that the energy flux also decreases remarkably owing to the confluence, that the energy flux also decreases remarkably owing to the confluence, and that the decreased values are approximately 40% of the efflux energy of the jet, independent of the ratio of a distance between two nozzles to the nozzle width and θ0. A method of predicting the velocity distribution also has been proposed. The predicted values agreed well with the experimental results.