Investigation of the Effect of Inlet Turbulence on Transitional Wall-Bounded Flows

2017 ◽  
Author(s):  
Burak Ahmet Tuna ◽  
Xianguo Li ◽  
Serhiy Yarusevych
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Initial Conditions ◽  
Hydraulic Diameter ◽  
Transition To Turbulence ◽  
Duct Flow ◽  
Entrance Length ◽  
Hot Wire ◽  
Boundary Layer Development ◽  
Layer Development

The present work investigates experimentally the effects of grid-generated turbulence on the transition and the hydrodynamic entrance length in a developing duct flow. Particle Image Velocimetry (PIV) and hot-wire anemometry are used to characterize the flow in a rectangular duct with a length of 1m (∼40Dh) and an aspect ratio of 2 (20mm × 40mm). The inlet turbulence intensity is controlled using different grids, and experiments are performed for a Reynolds number based on hydraulic diameter ReDh = 17,750. Hot-wire and PIV results show that the inlet turbulence intensity has a substantial effect on the flow evolution in the duct, as it substantially changes the boundary layer characteristics in the hydrodynamic entrance region. Analysis shows that, as expected, transition to turbulence advances upstream as the inlet turbulence intensity increases, leading to the decrease in the entrance length. The primary effect is confined to boundary layer development, as the turbulence intensity decays rapidly in the core flow, becoming independent of the initial conditions after about 10 hydraulic diameter (Dh) downstream from the grid. Thus, the analysis is focused on characterizing the boundary layer development and quantifying the associated changes in the flow development along the duct.

scholarly journals Effect of turbulence on the wake of a wall-mounted cube

2016 ◽  
Vol 804 ◽  
pp. 513-530 ◽  
Author(s):  
R. Jason Hearst ◽  
Guillaume Gomit ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Reattachment Length ◽  
Free Stream Turbulence ◽  
Boundary Layer Development ◽  
Image Velocimetry ◽  
Shedding Frequency ◽  
Layer Development

The influence of turbulence on the flow around a wall-mounted cube immersed in a turbulent boundary layer is investigated experimentally with particle image velocimetry and hot-wire anemometry. Free-stream turbulence is used to generate turbulent boundary layer profiles where the normalised shear at the cube height is fixed, but the turbulence intensity at the cube height is adjustable. The free-stream turbulence is generated with an active grid and the turbulent boundary layer is formed on an artificial floor in a wind tunnel. The boundary layer development Reynolds number ($Re_{x}$) and the ratio of the cube height ($h$) to the boundary layer thickness ($\unicode[STIX]{x1D6FF}$) are held constant at $Re_{x}=1.8\times 10^{6}$ and $h/\unicode[STIX]{x1D6FF}=0.47$. It is demonstrated that the stagnation point on the upstream side of the cube and the reattachment length in the wake of the cube are independent of the incoming profile for the conditions investigated here. In contrast, the wake length monotonically decreases for increasing turbulence intensity but fixed normalised shear – both quantities measured at the cube height. The wake shortening is a result of heightened turbulence levels promoting wake recovery from high local velocities and the reduction in strength of a dominant shedding frequency.

Numerical Simulation of Boundary Layer Variables Using ē–ε Closure Scheme

1995 ◽  
Vol 34 (2) ◽  
pp. 542-548 ◽  
Author(s):  
N. Ramanathan ◽  
K. Srinivasan ◽  
B. V. Seshasayee
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Initial Conditions ◽  
Closure Model ◽  
Model Simulations ◽  
First Order ◽  
Closure Scheme ◽  
Boundary Layer Development ◽  
History Of ◽  
Layer Development

Abstract In this study, a one-and-a-half-order ē–ε closure scheme is used to study the planetary boundary layer development over a full diurnal cycle using Wangara 33d-day observations as initial conditions. The simulated results are compared with a first-order closure model and higher-order closure model results. A scheme of this kind has the advantage of taking into account the history of turbulence state in terms of a prognostic equation for turbulence kinetic energy and provides a better basis for the representation of clouds. The results of the model simulations compare favorably with other investigators’ results.

The Use of Hot-Wire Anemometry to Investigate Unsteady Wake-Induced Boundary-Layer Development on a High Lift LP Turbine Cascade

2000 ◽  
Author(s):  
Stefan Wolff ◽  
Stefan Brunner ◽  
Leonhard Fottner
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Data Acquisition ◽  
Suction Side ◽  
Data Acquisition System ◽  
Hot Wire ◽  
Flow Conditions ◽  
Inlet Flow ◽  
Boundary Layer Development ◽  
Layer Development

Recent research has revealed positive effects of unsteady flow on the development of boundary layers in turbine cascades, especially at conditions with a laminar suction side separation bubble at low Reynolds-numbers. Compared to steady flow a reduction of total pressure loss coefficient over a broad range of Reynolds-numbers has been shown. Taking into account the positive effects of wake-induced transition already during the design process, new high lift bladings with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole turbine module for a constant stage loading. Unsteady flow in turbomachines is caused by the relative motion of rotor and stator rows. For simulating a moving blade row upstream of a linear cascade in the High Speed Cascade Wind Tunnel of the Universität der Bundeswehr München, a wake generator has been designed and built. The wakes are generated with bars, moving with a velocity of up to 40 m/s in the test section upstream of the cascade inlet plane. Unsteady flow causes the transition on the surface of the suction side of a low pressure turbine blade to move upstream whenever an incoming wake is present on the surface, moreover a laminar separation bubble can be diminished or even suppressed. In order to detect the effects of wakes on the boundary layer development a new hot-wire data acquisition system is required. Due to the fact that hot-wires give a good insight into boundary layer development a new hot-wire data acquisition system has been set up. The anemometry system is able of acquiring four channels simultaneously, therefore being capable of logging a triple hot-wire sensor and a bar trigger simultaneously. One further channel is utilised for a once-per revolution trigger. The once-per revolution trigger is used to start the measurement of one data block. Using the well established ensemble averaging technique, 300 ensembles each consisting of 5 wake passing periods have been acquired. Ensemble averaging can be directly performed without any data reduction. The adaptation of this new hot-wire anemometry data acquisition system to the High Speed Cascade Wind Tunnel of the Universität der Bundeswehr München is pointed out. First results on unsteady periodic boundary layer development of a highly loaded low pressure turbine cascade under unsteady inlet flow conditions are presented. During the present investigation four boundary layer traverses, ranging from x/lax = 0.82 to x/lax = 0.99 (suction side), at steady and unsteady inlet flow conditions (Ubar = 10 m/s) at an outlet Reynolds-number of Re2th = 100000 have been conducted.

Effect of Surface Roughness on Loss Behaviour, Aerodynamic Loading and Boundary Layer Development of a Low-Pressure Gas Turbine Airfoil

2010 ◽  
Author(s):  
Marco Montis ◽  
Reinhard Niehuis ◽  
Andreas Fiala
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Low Pressure ◽  
Test Facility ◽  
Hot Wire ◽  
Wire Probe ◽  
Aerodynamic Loading ◽  
Boundary Layer Development ◽  
Layer Development ◽  
Effect Of Surface

Aerodynamic measurements on the linear low-pressure turbine cascade T106C were conducted in a high speed test facility, in order to investigate the effect of surface roughness on loss behaviour, aerodynamic loading, and boundary layer development. Three different roughnesses were investigated, with a ratio of the center line average roughness to the profile chord of 0.8·10−5, 5·10−5 and 25·10−5. Tests were carried out under design outlet Mach number (Ma2th = 0.6), outlet Reynolds number ranging from Re2th = 5·104 to Re2th = 7·105 and inlet turbulence level Tu1 = 3% and Tu1 = 6%. The flow field downstream of the cascade and the loading distribution on the profiles were measured for each investigated operating point using five hole probes and surface static pressure taps. Additional measurements with a hot-wire probe in the suction surface (SS) boundary layer were also conducted, in order to investigate the differences in boundary layer development due to surface roughness. From loss and blade loading measurements it was found that roughness has no influence on the pressure distribution on the profile, although the highest investigated roughness produces a significant loss reduction at low Reynolds numbers. Hot-wire probe surveys show that at Re2th = 9·104 the boundary layer for the highest roughness immediately upstream of the flow separation point on the SS is substantially thinner than for the middle roughness and the smooth profile.

Investigation of the Effect of Inlet Turbulence and Reynolds Number on Developing Duct Flow

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Burak A. Tuna ◽  
Serhiy Yarusevych ◽  
Xianguo Li ◽  
Yi Ren ◽  
Fanghui Shi
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Turbulence Intensity ◽  
Substantial Effect ◽  
Layer Growth ◽  
Transition To Turbulence ◽  
Duct Flow ◽  
Layer Interaction ◽  
Laminar To Turbulent Transition

This study investigates experimentally the effects of upstream flow conditions and Reynolds number on a developing duct flow. Particle image velocimetry (PIV) and hot-wire (HW) anemometry are employed to explore the flow dynamics in a rectangular duct with an aspect ratio of 2 and a length of 40 hydraulic diameters (Dh). Experiments are employed for two Reynolds numbers, ReDh = 17,750 and 35,500 where the inlet turbulence intensity is controlled using different turbulence grids. The results show that the inlet turbulence intensity and Reynolds number have a substantial effect on the flow evolution, the onset of shear layer interaction zone, and the subsequent relaxation to the fully developed flow. The main effect is linked to the development of the boundary layer, as the turbulence intensity decays rapidly in the core flow. The detailed analysis indicates that transition to turbulence advances upstream as the inlet turbulence intensity is increased, leading to an earlier onset of shear layer interaction and the decrease in entrance length. A similar upstream advancement of laminar-to-turbulent transition is induced as the Reynolds number is increased. However, a delay in the onset of shear layer interaction regime is observed at higher Reynolds number due to lower overall boundary layer growth rate. Thus, the focus of the analysis characterization of the boundary layer development and quantification of the associated changes in the duct flow development.

The Use of Hot-Wire Anemometry to Investigate Unsteady Wake-Induced Boundary-Layer Development on a High-Lift LP Turbine Cascade

2000 ◽  
Vol 122 (4) ◽  
pp. 644-650 ◽  
Author(s):  
Stefan Wolff ◽  
Stefan Brunner ◽  
Leonhard Fottner
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Data Acquisition ◽  
Suction Side ◽  
Data Acquisition System ◽  
Hot Wire ◽  
Flow Conditions ◽  
Inlet Flow ◽  
Boundary Layer Development ◽  
Layer Development

Recent research has revealed positive effects of unsteady flow on the development of boundary layers in turbine cascades, especially at conditions with a laminar suction side separation bubble at low Reynolds numbers. Compared to steady flow, a reduction of total pressure loss coefficient over a broad range of Reynolds numbers has been shown. Taking into account the positive effects of wake-induced transition already during the design process, new high lift bladings with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole turbine module for a constant stage loading. Unsteady flow in turbomachines is caused by the relative motion of rotor and stator rows. For simulating a moving blade row upstream of a linear cascade in the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen, a wake generator has been designed and built. The wakes are generated with bars, moving with a velocity of up to 40 m/s in the test section upstream of the cascade inlet plane. Unsteady flow causes the transition on the surface of the suction side of a low-pressure turbine blade to move upstream whenever an incoming wake is present on the surface; moreover, a laminar separation bubble can be diminished or even suppressed. In order to detect the effects of wakes on the boundary layer development a new hot wire data acquisition system is required. Due to the fact that hot wires give a good insight into boundary layer development, a new hot-wire data acquisition system has been set up. The anemometry system can acquire four channels simultaneously, therefore being capable of logging a triple hot-wire sensor and a bar trigger simultaneously. One further channel is utilized for a once-per-revolution trigger. The once-per-revolution trigger is used to start the measurement of one data block. Using the well-established ensemble-averaging technique, 300 ensembles each consisting of five wake passing periods have been acquired. Ensemble averaging can be directly performed without any data reduction. The adaptation of this new hot-wire anemometry data acquisition system to the High-Speed Cascade Wind Tunnel of the Universita¨t der Bundeswehr Mu¨nchen is pointed out. First, results on unsteady periodic boundary layer development of a highly loaded low-pressure turbine cascade under unsteady inlet flow conditions are presented. During the present investigation four boundary layer traverses, ranging from x/lax=0.82 to x/lax=0.99 (suction side), at steady and unsteady inlet flow conditions Ubar=10 m/s at an outlet Reynolds number of Re2th=100,000 have been conducted. [S0889-504X(00)00204-X]

Assessing the Influence of Aerosol on Radiation and Its Roles in Planetary Boundary Layer Development

2021 ◽  
Vol 35 (2) ◽  
pp. 384-392
Author(s):  
Zhigang Cheng ◽  
Yubing Pan ◽  
Ju Li ◽  
Xingcan Jia ◽  
Xinyu Zhang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Boundary Layer Development ◽  
Layer Development

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Some Boundary Layer-Porous Wall Coupling Effects in Laminar Flows With Surface Injection

1970 ◽  
Vol 92 (3) ◽  
pp. 257-266
Author(s):  
D. A. Nealy ◽  
P. W. McFadden
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Balance ◽  
Transfer Problem ◽  
Porous Wall ◽  
Laminar Flows ◽  
Stream Velocity ◽  
Axial Conduction ◽  
Boundary Layer Development ◽  
Layer Development

Using the integral form of the laminar boundary layer thermal energy equation, a method is developed which permits calculation of thermal boundary layer development under more general conditions than heretofore treated in the literature. The local Stanton number is expressed in terms of the thermal convection thickness which reflects the cumulative effects of variable free stream velocity, surface temperature, and injection rate on boundary layer development. The boundary layer calculation is combined with the wall heat transfer problem through a coolant heat balance which includes the effect of axial conduction in the wall. The highly coupled boundary layer and wall heat balance equations are solved simultaneously using relatively straightforward numerical integration techniques. Calculated results exhibit good agreement with existing analytical and experimental results. The present results indicate that nonisothermal wall and axial conduction effects significantly affect local heat transfer rates.

Sign in / Sign up

Export Citation Format

Share Document