Jet Interaction in Cross Flow: Experimental and Numerical Model

2014 ◽  
Author(s):  
Celso Almeida ◽  
António A. Nunes ◽  
Senhorinha Teixeira ◽  
José Carlos Teixeira ◽  
Pedro Lobarinhas
Keyword(s):  
Wind Tunnel ◽  
Cross Section ◽  
Large Scale ◽  
Cfd Simulation ◽  
Free Stream ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Stream Velocity ◽  
Entire Cross Section ◽  
Injection Point

Ventilation of wide spaces often requires a correct mixing of a jet in a cross flow. The present paper describes the application of Computational Fluid Dynamics (CFD) to model the interaction of a free stream jet with a cross flow, taking into account temperature gradients between the two streams. The model uses the finite volume technique for solving the conservation equations of fluid: mass, momentum and energy. Buoyancy is described by the Boussinesq approximation. The convergence of the solution required a high mesh refinement in the region of flow interaction. The data were compared with experimental results obtained in a subsonic wind tunnel. The experiments were carried out along the 4.0 m long test section of a 1.4×0.8 low speed wind tunnel. The jets were injected at 90° through orifices 25 mm in diameter drawn from a plenum either at the same or higher temperature the free stream. The jet velocity to the free stream velocity ratio was set at 8 for a single jet and between 4 and 16 for multiple injections. Data include velocity, pressure and temperature. The results show that the injection of relatively small cross-flow rates can cause the development of large regions of interaction with the main flux, accompanied by the creation of large scale flow structures, which contribute effectively to rapid mixing of the two streams. A CFD simulation of temperature showed that a jet 30 diameters downstream (30D) is an extension of the plume covering almost half of the cross section and a good homogeneity, then the extension of the plume 120D which covers almost the entire cross section and an optimum mixing occurs. The CFD simulation temperature of 13 jets showed that a toroidal extension of the plume and a good homogenization as early as 30D downstream of the injection point, occurs.

scholarly journals Detailed Simulation of the Nominal Flow and Temperature Conditions in a Pre-Konvoi PWR Using Coupled CFD and Neutron Kinetics

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 161
Author(s):  
Thomas Höhne ◽  
Sören Kliem
Keyword(s):  
Cross Section ◽  
Power Distribution ◽  
Large Scale ◽  
Cfd Simulation ◽  
Cross Flow ◽  
Spacer Grid ◽  
Neutron Kinetics ◽  
Pressure Losses ◽  
The Core ◽  
Reactor Pressure

The aim of the numerical study was the detection of possible vortices in the upper part of the core of a Pre-Konvoi Pressurized Water Reactor (PWR) which could lead to temperature cycling. In addition, the practical application of this Computational Fluid Dynamic (CFD) simulation exists in the full 3D analysis of the coolant flow behavior in the reactor pressure vessel of a nuclear PWR. It also helps to improve the design of future reactor types. Therefore, a CFD simulation of the flow conditions was carried out based on a complex 3D model. The geometry of the model includes the entire Reactor Pressure Vessel (RPV) plus all relevant internals. The core is modelled using the porous body approach, the different pressure losses along and transverse to the main flow direction were considered. The spacer-grid levels were taken into account to the extent that in these areas no cross-flow is possible. The calculation was carried out for nominal operating conditions, i.e., for full load operation. Furthermore, a prototypical End of Cycle (EOC) power distribution was assumed. For this, a power distribution was applied as obtained from a stationary full-core calculation with the 3D neutron kinetics code DYN3D. In order to be able to adequately reproduce flow vortexes, the calculation was performed transiently with suitable Detached Eddy Simulations (DES) turbulence models. The calculation showed fluctuating transverse flow in the upper part of the core, starting at the 8th spacer grid but also revealed that no large dominant vortices exists in this region. It seems that the core acts as a rectifier attenuating large-scale vortices. The analyses included several spacer grid levels in the core and showed that in some areas of the core cross-section an upward increasingly directed transversal flow to the outlet nozzle occurs. In other areas of the core cross-section, on the other hand, there is nearly any cross-flow. However, the following limitations of the model apply: In the model all fuel elements are treated identical and cross flows due to different axial pressure losses for different FA types cannot be displayed. The complex structure of the FAs (eg. flow vanes in spacer grids) could also influence the formation of large-scale vortices. Also, the possible influence of two-phase flows was not considered.

Measurements of a Wall Jet Impinging Onto a Forward Facing Step

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
D. C. Langer ◽  
B. A. Fleck ◽  
D. J. Wilson
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Cfd Simulation ◽  
Velocity Ratio ◽  
Water Channel ◽  
Cross Flow ◽  
Elliptical Cross Section ◽  
Navier Stokes ◽  
Wall Jet ◽  
Elliptical Cross

This study examines a horizontal wall jet impinging onto a forward facing vertical step in a cross-flow. Planar laser induced fluorescence (PLIF) experiments in a 68×40 mm2 water channel indicate how the wall-jet flow after impinging onto the step becomes a vertical jet with an elliptical cross section. This study proposes predictive empirical correlations for the aspect ratio and perimeter of the jet’s elliptical cross section based on the step geometry and the inlet flow conditions. A numerical model is also presented, which was produced from a commercial Reynolds averaged Navier–Stokes computational fluid dynamics (CFD) code with the k-ϵ closure model. The experimental results were well represented by correlations for the perimeter P and aspect ratio S using the parameters H (the step height), L∘ (the distance from the jet represented as a point source to the step), and R (the velocity ratio). The CFD simulation was able to predict the trends in the perimeter (under different conditions), aspect ratio, and the shape of the concentration profile, but overpredicted the jet’s perimeter by approximately 50%. The results of these tests are required as input parameters when modeling jet trajectories.

A new boundary layer wind tunnel

1988 ◽  
Vol 92 (916) ◽  
pp. 224-229
Author(s):  
P. E. Roach
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Test Section ◽  
Gas Turbines ◽  
Large Scale ◽  
Free Stream ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Dimensional Boundary

Summary The procedures employed for the design of a closed-circuit, boundary layer wind tunnel are described. The tunnel was designed for the generation of relatively large-scale, two-dimensional boundary layers with Reynolds numbers, pressure gradients and free-stream turbulence levels typical of the turbomachinery environment. The results of a series of tests to evaluate the tunnel performance are also described. The flow in the test section is shown to be highly uniform and steady, with very low (natural) free-stream turbulence intensities. Measured boundary layer mean and fluctuating velocity profiles were found to be in good agreement with classical correlations. Test-section free-stream turbulence intensities are presented for grid-generated turbulence: agreement with expectation is again found to be good. Immediate applications to the tunnel include friction drag reduction and boundary layer transition studies, with future possibilities including flow separation and other complex flows typical of those found in gas turbines.

Boundary Layer Calculation for Analysis and Design

1978 ◽  
Vol 100 (2) ◽  
pp. 232-236 ◽  
Author(s):  
H. E. Weber
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Free Stream ◽  
Cross Flow ◽  
Semiempirical Method ◽  
Stream Velocity ◽  
Potential Core ◽  
Analysis And Design ◽  
Inlet Conditions

A simple, semiempirical method for calculating the laminar, transition, and turbulent boundary layer with arbitrary free stream pressure gradient is developed. Good correlation is obtained with data on general two dimensional turbulent flows, diffuser flows, and the cylinder in cross-flow. However only for the diffuser has the boundary layer flow been coupled with the potential core so that only the inlet conditions and geometry are required. In other cases the free stream velocity distribution must be known or calculable. Skin friction coefficient, momentum thickness Reynolds number, and free stream pressure gradient parameter correlation employs a simple lag theory. With the integral momentum equation the complete boundary layer parameters are obtained as functions of the distance along a surface.

Feasibility investigation of large-scale model suspended by cable-driven parallel robot in hypersonic wind tunnel test

2016 ◽  
Vol 231 (13) ◽  
pp. 2375-2383 ◽  
Author(s):  
Xiaoguang Wang ◽  
Miaojiao Peng ◽  
Zhenghong Hu ◽  
Yueshi Chen ◽  
Qi Lin
Keyword(s):  
Wind Tunnel ◽  
Large Scale ◽  
Cfd Simulation ◽  
Aerodynamic Force ◽  
Wind Tunnel Test ◽  
Special Kind ◽  
Parallel Robot ◽  
Scale Model ◽  
Hypersonic Wind Tunnel ◽  
Large Scale Model

Cable-driven parallel robot is a special kind of robot, which is actuated by cables. It is already applied in the low speed wind tunnel to get aerodynamic measurement of aircraft model, and the aircraft pose could be adjusted by changing the cable length. Whether it can be used in hypersonic wind tunnel still needs further discussion. This paper presents the dynamics and aerodynamics analysis of a large-scale model supported by 6-DOF cable-driven parallel robot to investigate the feasibility of this special kind of suspension system in hypersonic wind tunnel. The description of this setup with a X-51A-like model is given, and then based on the system dynamic equations, aerodynamic force and stiffness matrix are derived. In the simulation, properties of dynamics and aerodynamics are mainly concerned. A typical shock tunnel with flow duration of about 100 milliseconds is taken as an example, and results show that the system is stable enough to meet the fundamental static wind tunnel test. From the cable tension variation under impact load and the sensitivity analysis, it is likely accessible to derive the aerodynamic forces. Compared with the sting suspension method, cable-driven parallel robot has the priority of higher inherent frequency and more flexible degrees. The interference to the flow field induced by cables is also preliminarily proved to be small by the CFD simulation, which can be acceptable and corrected. Researches conducted show the feasibility of cable-driven parallel robot’s application in hypersonic wind tunnel.

Three-dimensional laminar boundary layers in crosswise pressure gradients

1974 ◽  
Vol 66 (4) ◽  
pp. 641-655 ◽  
Author(s):  
J. H. Horlock ◽  
A. K. Lewkowicz ◽  
J. Wordsworth
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Three Dimensional ◽  
Cross Flow ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Laminar Boundary Layers ◽  
The Cross

Two attempts were made to develop a three-dimensional laminar boundary layer in the flow over a flat plate in a curved duct, establishing a negligible streamwise pressure gradient and, at the same time, an appreciable crosswise pressure gradient.A first series of measurements was undertaken keeping the free-stream velocity at about 30 ft/s; the boundary layer was expected to be laminar, but appears to have been transitional. As was to be expected, the cross-flow in the boundary layer decreased gradually as the flow became progressively more turbulent.In a second experiment, at a lower free-stream velocity of approximately 10 ft/s, the boundary layer was laminar. Its streamwise profile resembled closely the Blasius form, but the cross-flow near the edge of the boundary layer appears to have exceeded that predicted theoretically. However, there was a substantial experimental scatter in the measurements of the yaw angle, which in laminar boundary layers is difficult to obtain accurately.

Performance Impacts Due to Wake Mixing in Axial-Flow Turbomachinery

2006 ◽  
Author(s):  
T. J. Praisner ◽  
J. P. Clark ◽  
T. C. Nash ◽  
M. J. Rice ◽  
E. A. Grover
Keyword(s):  
Free Stream ◽  
Velocity Ratio ◽  
Axial Flow ◽  
Extraction Process ◽  
Stream Velocity ◽  
Cfd Simulations ◽  
Stream Tube ◽  
Blade Row ◽  
Stream Tubes ◽  
Mixing Losses

One of the last loss mechanisms remaining to be quantified and correlated for inclusion in meanline predictive systems concerns the mixing of wakes across downstream airfoil rows. Here, we demonstrate that the unsteady losses incurred as turbomachinery wakes mix in downstream rows are a function of the velocity ratio across the downstream row as calculated in the frame of reference of wake generation. Analytical and computational results, compared to measurements of wakes mixing under variable free-stream velocity conditions, reveal that wake-loss modification is primarily a result of an inviscid dilation of the stream tubes that comprise the wake fluid. Further, simulations of wakes exposed to a range of turbomachinery-specific velocity ratios indicate that wake-loss augmentation caused by stream-tube dilation is significantly more pronounced than wake-loss reductions imparted by stream-tube contraction. It is demonstrated that wakes in turbines are dilated in the adjacent downstream row, whether it is a vane or a blade row, through a work extraction process that occurs in the wake-generation reference frame. Finally, comparisons between rig data and CFD simulations suggest that wake-mixing losses, enhanced by downstream rows, can contribute as much as 1.5 percent of lost efficiency in multistage low-pressure turbines.

Free-stream turbulence and the development of cross-flow disturbances

2013 ◽  
Vol 735 ◽  
pp. 347-380 ◽  
Author(s):  
Robert S. Downs ◽  
Edward B. White
Keyword(s):  
Surface Roughness ◽  
Flow Problem ◽  
Free Stream ◽  
Flow Instability ◽  
Cross Flow ◽  
Stream Velocity ◽  
Swept Wing ◽  
Free Stream Turbulence ◽  
Flow Disturbances ◽  
The Cross

AbstractThe cross-flow instability that arises in swept-wing boundary layers has resisted attempts to describe the path from disturbance initiation to transition. Following concerted research efforts, surface roughness and free-stream turbulence have been identified as the leading providers of initial disturbances for cross-flow instability growth. Although a significant body of work examines the role of free-stream turbulence in the cross-flow problem, the data more relevant to the flight environment (turbulence intensities less than 0.07 %) are sparse. A series of recent experiments indicates that variations within this range may affect the initiation or growth of cross-flow instability amplitudes, hindering comparison among results obtained in different disturbance environments. To address this problem, a series of wind tunnel experiments is performed in which the free-stream turbulence intensity is varied between 0.02 % and 0.2 % of free-stream velocity,${U}_{\infty } $. Measurements of the stationary and travelling mode amplitudes are made in the boundary layer of a 1.83 m chord,$45{{}^\circ} $swept-wing model. These results are compared to those of similar experiments at higher turbulence levels to broaden the current knowledge of this portion of the cross-flow problem. It is observed that both free-stream turbulence and surface roughness contribute to the initiation of unsteady disturbances, and that free-stream turbulence affects the development of both stationary and unsteady cross-flow disturbances. For the range tested, enhanced free-stream turbulence advances the transition location except when a subcritically spaced roughness array is employed.

Numerical investigation of the flow dynamics past a three-element aerofoil

2013 ◽  
Vol 732 ◽  
pp. 401-444 ◽  
Author(s):  
Sébastien Deck ◽  
Romain Laraufie
Keyword(s):  
Numerical Investigation ◽  
Large Scale ◽  
Free Stream ◽  
Pressure Fluctuations ◽  
Phase Relationship ◽  
Feedback Mechanism ◽  
Flow Dynamics ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Detached Eddy Simulation

AbstractA numerical investigation of the flow dynamics around a two-dimensional high-lift configuration was carried out by means of a zonal detached eddy simulation (ZDES) technique for flow conditions corresponding to aircraft approach. Both slat and flap regions have been scrutinized and compared with experimental data available in the literature. It is shown that slat and flap coves behave like shallow cavities. The distance between the upstream cusp and the downstream edge is the relevant length scale for each cove taken separately. Consistently with previous findings, this study indicates that the maximum of the broadband spectrum of slat (respectively flap) pressure fluctuations occurs for Strouhal numbers $0. 5\leq \mathit{St}\leq 4$ when based on slat chord (respectively on flap chord) and free-stream velocity. It is shown that mode $(n)$ of the slat cove and mode $(n+ 1)$ of the flap cove are very close making a coherent phase relationship possible. A large-scale coupled self-sustained oscillations mechanism between slat and flap cavities, evidenced by spectral analysis, occurs at a Strouhal number $\mathit{St}= 3{\unicode{x2013}} 6$ based on the main wing chord and free-stream velocity. This yields to an acoustic feedback mechanism characterized by a normalized frequency depending on the free stream Mach number like $\mathit{St}= (1- { M}_{0}^{2} )/ 2{M}_{0} $. The present result appears to line up with the findings by Hein et al. (J. Fluid Mech., vol. 582, 2007, pp. 179–202) who showed that two types of resonance could exist: surface waves ones, scaling with the total aerofoil length and longitudinal cavity-type resonances, scaling with the slat cove length.

INFLUENCE OF THE INLET SHAPE ON THE PERFORMANCE OF DOUBLE OFFSET TRANSITION S-DUCT WITH DIFFUSION

2008 ◽  
Vol 05 (01) ◽  
pp. 1-19 ◽  
Author(s):  
RAJESH KUMAR SINGH ◽  
SIDHNATH SINGH ◽  
V. SESHADRI
Keyword(s):  
Total Pressure ◽  
Free Stream ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Cross Flow ◽  
Area Ratio ◽  
Stream Velocity ◽  
Crucial Component ◽  
Flow Investigation ◽  
Cross Flow Velocity

Transition S-shaped intake duct is a crucial component of dual engine used in modern combat aircrafts. Present flow investigation demonstrates the flow behavior of double offset transition S-duct for different inlet geometries having circular exit (ϕ = 72.5 mm) and uniform roughness. The inlet geometries namely rectangular, square, elliptical, oval, and semicircular have been analyzed for double offset transition S-duct having 300 mm centerline length and an area ratio of 2.0. Incompressible flow analysis carried out for free stream velocity at 30 m/s with RNG k–ε turbulence model has shown that the elliptical inlet shape gives the best performance whereas square inlet gives the worst performance in terms of longitudinal and cross-flow velocity distribution, pressure recovery, total pressure loss, distortion coefficient, and swirl coefficient at the exit of the duct.

Sign in / Sign up

Export Citation Format

Share Document