An Experimental Study of Artificially-Generated Turbulent Spots Under Strong Favorable Pressure Gradients and Freestream Turbulence

2006 ◽  
Vol 129 (5) ◽  
pp. 563-572 ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Velocity Structure ◽  
Three Dimensional ◽  
Internal Flow ◽  
Leading Edge ◽  
Streamwise Velocity ◽  
Test Surface ◽  
Freestream Turbulence ◽  
Turbulent Spot ◽  
Turbulent Spots ◽  
Acceleration Rate

This paper presents experimental results on the internal flow structure of turbulent spots, and examines the sensitivity of this structure to streamwise acceleration rate and freestream turbulence. Measurements were performed on a flat plate, with two levels of freestream acceleration rate and three levels of freestream turbulence. The turbulent spots were generated artificially at a fixed distance from the test-surface leading edge, and the development of the spot was documented through hotwire measurements at three streamwise locations. The measurements were performed at multiple spanwise locations to allow observation of the three-dimensional spatial structure of the turbulent spot and the temporal evolution of this structure. Analysis of the perturbation velocity and rms velocity fluctuations provides insight into the variations of the streaky streamwise-velocity structure within the turbulent spot, with a focus on the effects of freestream acceleration rate and turbulence level.

Time-Split Inflow Boundary Treatment

1985 ◽  
Author(s):  
Siu Shing Tong
Keyword(s):  
Three Dimensional ◽  
Internal Flow ◽  
Leading Edge ◽  
Two Dimensional ◽  
Governing Equations ◽  
Internal Flows ◽  
One Dimensional ◽  
Boundary Treatment

This paper describes a new non-reflective inflow treatment for viscous and inviscid internal flow calculations. The method approximates the multi-dimensional governing equations at the inflow boundary in a series of one-dimensional split equations. This treatment allows the artificial inflow boundary to be brought in just in front of the leading edge, while allowing upstream running waves to penetrate without significant reflection. Calculation examples of two dimensional inviscid internal flows are presented. Extension of the method to three-dimensional problems is also discussed.

Unsteady and Three-Dimensional Flow Phenomena in a Transonic Centrifugal Compressor Impeller at Rotating Stall

2009 ◽  
Author(s):  
Kenichiro Iwakiri ◽  
Masato Furukawa ◽  
Seiichi Ibaraki ◽  
Isao Tomita
Keyword(s):  
Centrifugal Compressor ◽  
Wavelet Transforms ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Internal Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Detached Eddy Simulation ◽  
Transonic Centrifugal Compressor ◽  
Compressor Impeller

This paper presents a combined experimental and numerical analysis of rotating stall in a transonic centrifugal compressor impeller for automotive turbochargers. Stall characteristics of the compressor were examined by two high-response pressure transducers mounted on the casing wall near the impeller inlet. The pressure traces were analyzed by wavelet transforms to estimate the disturbance waves quantitatively. Three-dimensional unsteady internal flow fields were simulated numerically by Detached Eddy Simulation (DES) coupled LES-RANS approach. The analysis results show good agreements on both compressor performance characteristics and the unsteady flow features at the rotating stall. At stall inception, spiral-type breakdown of the full-blade tip leakage vortex was found out at some passages and the brokendown regions propagated against the impeller rotation. This phenomenon changed with throttling, and tornado-type separation vortex caused by the full-blade leading edge separation dominated the flow field at developed stall condition. It is similar to the flow model of short-length scale rotating stall established in an axial compressor rotor.

Three-dimensional boundary-layer instability and separation induced by small-amplitude streamwise vorticity in the upstream flow

1993 ◽  
Vol 246 ◽  
pp. 21-41 ◽  
Author(s):  
M. E. Goldstein ◽  
S. J. Leib
Keyword(s):  
Boundary Layer ◽  
Small Amplitude ◽  
Three Dimensional ◽  
Cross Flow ◽  
Leading Edge ◽  
Streamwise Velocity ◽  
Linear Perturbation ◽  
Streamwise Vorticity ◽  
Dimensional Boundary ◽  
Layer Flow

We consider the effects of a small-amplitude, steady, streamwise vorticity field on the flow over an infinitely thin flat plate in an otherwise uniform stream. We show how the initially linear perturbation, ultimately leads to a small-amplitude but nonlinear cross-flow far downstream from the leading edge. This motion is imposed on the boundary-layer flow and eventually causes the boundary layer to separate. The streamwise velocity profiles within the boundary layer become inflexional in localized spanwise regions just upstream of the separation point. The flow in these regions is therefore susceptible to rapidly growing inviscid instabilities.

Simulations of Slot Film-Cooling With Freestream Acceleration and Turbulence

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Yousef Kanani ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Leading Edge ◽  
Test Surface ◽  
Freestream Turbulence ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Pin Fins ◽  
Turbulence Condition ◽  
Slot Film Cooling

Slot film cooling in an accelerating boundary layer with high freestream turbulence is studied numerically using large eddy simulations (LES). Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. The synthetic eddy method is used to generate different levels of turbulence and length scales at the inflow cross-plane. Calculations are done for a Reynolds number of 250,000 and freestream turbulence levels of 0.7%, 3.5%, 7.8%, and 13.7% to predict both film cooling effectiveness and heat transfer coefficient over the test surface. These conditions correspond to the experimental measurements of (Busche, M. L., Kingery, J. E., and Ames, F. E., 2014, “Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence,” ASME Paper No. GT2014-25360.) Numerical results show good agreement with measurements and show the observed decay of thermal effectiveness and increase of Stanton number with turbulence intensity. Velocity and turbulence exiting the slot are nonuniform laterally due to the presence of pin fins in the plenum feeding the slot which creates a nonuniform surface temperature distribution. No transition to fully turbulent boundary layer is observed throughout the numerical domain. However, freestream turbulence increases wall shear stress downstream driving the velocity profiles toward the turbulent profile and counteracts the laminarizing effects of the favorable pressure gradient. The effective Prandtl number decreases with freestream turbulence. The temperature profiles deviate from the self-similar profile measured under low freestream turbulence condition, reflecting the role of the increased diffusivity in the boundary layer at higher freestream turbulence.

Performance Evaluation of an Internal Flow Navier-Stokes Solver for Compressible Viscous Flow Simulations

2002 ◽  
Author(s):  
H. Tug˘rul Tınaztepe ◽  
Ahmet S¸. U¨c¸er ◽  
I˙. Sinan Akamandor
Keyword(s):  
Flow Field ◽  
Separation Bubble ◽  
Turbulent Viscosity ◽  
Three Dimensional ◽  
Internal Flow ◽  
Leading Edge ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Local Scaling ◽  
Characteristic Boundary

A three-dimensional compressible full Navier-Stokes solver is developed for the analysis of the flow field inside turbomachinary cascades. The solver uses an explicit second order accurate (cell-vertex) finite volume Lax-Wendroff scheme over hexahedral cells. The viscous and heat conduction terms are discretized in conservative form at the cell center. Second and fourth order numerical smoothing terms are added with local scaling factors. Eddy viscosity is calculated by the Baldwin-Lomax model and is adapted to the pointered cell based algorithm. Turbulent viscosity is blended by inverse distance square weighting functions near corners. Characteristic boundary conditions are used. A computational analysis has been carried out to present the capability of the solver in capturing secondary velocity patterns, flow angles and total pressure loss distributions inside a linear high turning turbine cascade. A controlled diffusion compressor cascade at high incidence has been analyzed. Main features of the flow field in this compressor cascade were resolved (secondary and end wall flows and leading edge laminar separation bubble) as in the experimental data. The main aim of the work is to demonstrate the performance of the code in capturing the details of the complicated flow fields using grids that can be regarded as coarse.

scholarly journals Numerical Flow Simulation in a Centrifugal Pump at Design and Off-Design Conditions

2007 ◽  
Vol 2007 ◽  
pp. 1-8 ◽  
Author(s):  
K. W. Cheah ◽  
T. S. Lee ◽  
S. H. Winoto ◽  
Z. M. Zhao
Keyword(s):  
Centrifugal Pump ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Internal Flow ◽  
Leading Edge ◽  
Design Flow ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Pump Impeller ◽  
Rate Condition

The current investigation is aimed to simulate the complex internal flow in a centrifugal pump impeller with six twisted blades by using a three-dimensional Navier-Stokes code with a standardk-εtwo-equation turbulence model. Different flow rates were specified at inlet boundary to predict the characteristics of the pump. A detailed analysis of the results at design load,Qdesign, and off-design conditions, Q = 0.43Qdesignand Q = 1.45Qdesign, is presented. From the numerical simulation, it shows that the impeller passage flow at design point is quite smooth and follows the curvature of the blade. However, flow separation is observed at the leading edge due to nontangential inflow condition. The flow pattern changed significantly inside the volute as well, with double vortical flow structures formed at cutwater and slowly evolved into a single vortical structure at the volute diffuser. For the pressure distribution, the pressure increases gradually along streamwise direction in the impeller passages. When the centrifugal pump is operating under off-design flow rate condition, unsteady flow developed in the impeller passage and the volute casing.

scholarly journals Navier-Stokes Analysis of Turbine Blade Heat Transfer

1990 ◽  
Author(s):  
R. J. Boyle
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Freestream Turbulence ◽  
Eddy Viscosity Model ◽  
Experimental Heat ◽  
Experimental Heat Transfer

Comparisons with experimental heat transfer and surface pressures were made for seven turbine vane and blade geometries using a quasi-three-dimensional thin-layer Navier-Stokes analysis. Comparisons are made for cases with both separated and unseparated flow over a range of Reynolds numbers and freestream turbulence intensities. The analysis used a modified Baldwin-Lomax turbulent eddy viscosity model. Modifications were made to account for the effects of: 1) freestream turbulence on both transition and leading edge heat transfer; 2) strong favorable pressure gradients on re-laminarization; and 3) variable turbulent Prandtl number on heat transfer. In addition, the effect on heat transfer of the near-wall model of Deissler is compared with the Van Driest model.

The Three Dimensional Flow Structure and Turbulence in the Tip Region of an Axial Flow Compressor

2015 ◽  
Author(s):  
David Tan ◽  
Yuanchao Li ◽  
Huang Chen ◽  
Ian Wilkes ◽  
Joseph Katz
Keyword(s):  
Refractive Index ◽  
Shear Layer ◽  
Flow Rate ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Streamwise Velocity ◽  
Leakage Flow ◽  
Single Structure

Continuing preliminary data submitted last year, this paper focuses on effect of operation point on the structure of a tip leakage vortex (TLV) in compressor-like settings. Experiments are being performed at the Johns Hopkins University refractive index-matched facility. The transparent acrylic blades of the one and a half stage compressor have the same geometry, but lower aspect ratio as the inlet guide vanes and the first stage of the Low Speed Axial Compressor facility at NASA Glenn. The refractive index of the liquid, an aqueous NaI solution is matched with that of the blades and transparent casing, facilitating unobstructed stereo-PIV measurements. As the flow rate is reduced close to stall conditions, the leakage flow is confined to rotor chordwise sections further towards the leading edge, and the TLV rollup occurs further upstream, and more radially inward. However, as the leakage flow stops in the aft part of the passage, the near-stall TLV migrates faster to the PS side of the next blade. Instantaneous realizations demonstrate that the TLV consists of multiple interlaced vortices and never rolls up into a single structure, but when phased-averaged, it appears as single structure. The circumferential velocity peak is located radially inward of the mean vorticity center. Turbulent kinetic energy (TKE) is high in the TLV center, in the shear layer connecting the suction side (SS) corner to the TLV feeding vorticity into it, as well as in the region of flow separation on the endwall casing where the leakage flow meets the passage flow. The normal and shear Reynolds stress demonstrate high inhomogeneity and anisotropy, with the streamwise velocity fluctuations being the largest contributor to TKE. The dominant inplane contributors to TKE production rate involve contraction in the region of endwall casing separation and near the SS tip corner, and shear production in the shear layer. Fragmentation and rapid growth of the TLV occurs at mid passage, moving upstream with decreasing flow rate.

A visual study of turbulent spots

1981 ◽  
Vol 104 ◽  
pp. 387-405 ◽  
Author(s):  
A. E. Perry ◽  
T. T. Lim ◽  
E. W. Teh
Keyword(s):  
Flow Visualization ◽  
Boundary Layers ◽  
Three Dimensional ◽  
Basic Structure ◽  
Turbulent Boundary Layers ◽  
Wall Jet ◽  
Turbulent Spot ◽  
Turbulent Spots ◽  
Visual Study ◽  
Visualization Experiment

From the results of a flow visualization experiment, certain physical characteristics of a turbulent spot are suggested by the authors. The spot was artificially initiated at a point by a small intermittent wall jet. The authors also carried out experiments behind vibrating trip wires and observed the ‘signatures’ or ‘footprints’ of the A-shaped vortices seen by other workers. The fact that these ‘signatures’ are also observed in a turbulent spot leads one to suspect that these spots consist essentially of an array of A-shaped vortices. The formation of the spot is subsequently described in terms of three-dimensional disturbances of the cross-stream vortex filaments.The basic structure of the turbulent spot proposed here is similar to the suggested structure of fully developed turbulent boundary layers first put forward by Theodorsen (1955) and more recently by Bandyopadhyay & Head (1979).

Experimental and Numerical Analysis of a Motorcycle Air Intake System Aerodynamics and Performance

2020 ◽  
Vol 17 (1) ◽  
Author(s):  
M. A. Abd Halim ◽  
N. A. R. Nik Mohd ◽  
M. N. Mohd Nasir ◽  
M. N. Dahalan
Keyword(s):  
Combustion Process ◽  
Three Dimensional ◽  
Engine Performance ◽  
Internal Flow ◽  
Rapid Expansion ◽  
Navier Stokes ◽  
Turbulent Fluctuation ◽  
Ansys Fluent ◽  
Induction System ◽  
Acceleration And Deceleration

Induction system or also known as the breathing system is a sub-component of the internal combustion system that supplies clean air for the combustion process. A good design of the induction system would be able to supply the air with adequate pressure, temperature and density for the combustion process to optimizing the engine performance. The induction system has an internal flow problem with a geometry that has rapid expansion or diverging and converging sections that may lead to sudden acceleration and deceleration of flow, flow separation and cause excessive turbulent fluctuation in the system. The aerodynamic performance of these induction systems influences the pressure drop effect and thus the engine performance. Therefore, in this work, the aerodynamics of motorcycle induction systems is to be investigated for a range of Cubic Feet per Minute (CFM). A three-dimensional simulation of the flow inside a generic 4-stroke motorcycle airbox were done using Reynolds-Averaged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) solver in ANSYS Fluent version 11. The simulation results are validated by an experimental study performed using a flow bench. The study shows that the difference of the validation is 1.54% in average at the total pressure outlet. A potential improvement to the system have been observed and can be done to suit motorsports applications.

Sign in / Sign up

Export Citation Format

Share Document