RANS prediction of open jet aerofoil interaction and design metrics

2019 ◽  
Vol 123 (1266) ◽  
pp. 1275-1296
Author(s):  
A. A. Sheikh Al-Shabab ◽  
P. G. Tucker
Keyword(s):  
Interaction Analysis ◽  
Separation Bubble ◽  
Simulation Method ◽  
Suction Surface ◽  
Design Metrics ◽  
Surface Separation ◽  
Main Challenge ◽  
Boundary Layer Development ◽  
Rans Models ◽  
The Cost

ABSTRACTRANS models remain an attractive turbulence simulation method which could provide some open jet aerofoil interaction analysis at a fraction of the cost of a high-fidelity LES approach. The present work explores the potential and limitations of RANS in this context by simulating an open jet aerofoil noise experiment using the aerospace oriented Menter SST RANS model. This model’s tendency to transition at a critical Reynolds number lower than the experimental value was found to impact the boundary layer development. However, the introduction of a low-Re correction improved the prediction of surface pressure and skin friction, enabling the suction surface separation bubble to be captured. The free shear layer’s virtual origin characteristics exhibited sensitivity to the interaction with the aerofoil, which can be developed into a metric of the interaction. The main challenge for RANS was accounting for the rise in background disturbance level in the working section, which is caused by the high-turbulence intensity in the free shear layers.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Vol 126 (4) ◽  
pp. 663-676 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and reattachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Large-Eddy Simulation and Passive Control of Flows for a Low Pressure Turbine Cascade

2009 ◽  
Author(s):  
Jibing Lan ◽  
Yonghui Xie ◽  
Di Zhang ◽  
Jing Shu
Keyword(s):  
Pressure Fluctuation ◽  
Passive Control ◽  
Static Pressure ◽  
Separation Bubble ◽  
Suction Surface ◽  
Surface Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Fluctuation Frequency

A rectangular bar which just likes a forward-backward facing step was designed to passive control of the Low-Pressure Turbine (LPT) PakB cascade suction surface separation. Large-eddy simulation (LES) was adopted to analyze the separated-transition flows for the PakB cascade with and without the rectangular bar at Re (Reynolds number based on inlet condition and axial chord) of 86,000 and the freestream turbulence intensity of 1%. Computed results of uncontrolled condition agree well with the experimental data of Lake et al.[6, 7]. And the LES results shown that the rectangular bar control device was successful to control the LPT cascade suction surface separation and provides about 10% kinetic loss coefficient reduction from the uncontrolled one. Unsteady flow structures were also investigated in detail. Static pressure fluctuation frequency at six locations, ranging from 0.56Cx to 0.95Cx axial chord location and with a constant wall normal distance y/h = 1.0, was the same to the separation bubble vortex shedding frequency. Unsteady fluctuation velocity was examined too, which confirmed that the separation bubble vortex frequency was the same to the suction surface static pressure fluctuation frequency.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Re-Attachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Effects of Turbulence and Solidity on the Boundary Layer Development in a Low Pressure Turbine

2000 ◽  
Author(s):  
W. J. Solomon
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Suction Surface ◽  
Layer Transition ◽  
Laminar Separation ◽  
Second Stage ◽  
Boundary Layer Development ◽  
Layer Development

Multiple-element surface hot-film instrumentation has been used to investigate boundary layer development in the 2 stage Low Speed Research Turbine (LSRT). Measurements from instrumentation located along the suction surface of the second stage nozzle at mid-span are presented. These results contrast the unsteady, wake-induced boundary layer transition behaviour for various turbine configurations. The boundary layer development on two new turbine blading configurations with identical design vector diagrams but substantially different loading levels are compared with a previously published result. For the conventional loading (Zweifel coefficient) designs, the boundary layer transition occurred without laminar separation. At reduced solidity, wake-induced transition started upstream of a laminar separation line and an intermittent separation bubble developed between the wake-influenced areas. A turbulence grid was installed upstream of the LSRT turbine inlet to increase the turbulence level from about 1% for clean-inlet to about 5% with the grid. The effect of turbulence on the transition onset location was smaller for the reduced solidity design than the baseline. At the high turbulence level, the amplitude of the streamwise fluctuation of the wake-induced transition onset point was reduced considerably. By clocking the first stage nozzle row relative to the second, the alignment of the wake-street from the first stage nozzle with the suction surface of the second stage nozzle was varied. At particular wake clocking alignments, the periodicity of wake induced transition was almost completely eliminated.

The Influence of Different Endwall Contouring Locations on the Secondary Flow Losses in a Highly Loaded Low Pressure Turbine

2018 ◽  
Author(s):  
Wenhua Duan ◽  
Weiyang Qiao ◽  
Zuojun Wei ◽  
Jian Liu ◽  
Haoyi Cheng
Keyword(s):  
Secondary Flow ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Leading Edge ◽  
Low Pressure ◽  
Suction Surface ◽  
Surface Separation ◽  
Flow Losses ◽  
Endwall Contouring ◽  
Highly Loaded

A detailed experimental and numerical investigation of the effect of endwall contouring on the secondary flow was performed in a highly loaded low pressure linear cascade. A comparison between a planar and three contoured configurations has been performed, and the three-dimensional endwall secondary flow structures and the secondary flow losses are here analyzed and discussed. For the contoured endwall, three locations of the same contouring were investigated, first one with the contouring starting upstream the airfoil and ending just before the leading edge of the airfoil, secondary one with the contouring starting upstream the airfoil and ending in the middle of the airfoil passage, the last one with the contouring starting just from the leading edge of the airfoil and continuing through the airfoil passage just ending at the trailing edge. The results suggest that the numerical results offer a reliable prediction for the endwall secondary flow structure together with suction surface separation bubble. It was found that all the three locations of contouring could reduce the secondary flow losses effectively. The location through the airfoil passage got the most benefit in the reduction of secondary flow losses whereas the all contouring upstream the airfoil location got the least. It was also found that the profile losses was affected by the contoured endwall.

scholarly journals Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-Attachment Along the Suction Surface of a Low Pressure Turbine Blade

2005 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re = 110,000.

scholarly journals Uncertainty Cost Functions in Climate-Dependent Controllable Loads in Commercial Environments

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2885
Author(s):  
Daniel Losada ◽  
Ameena Al-Sumaiti ◽  
Sergio Rivera
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Simulation Method ◽  
Electricity Sector ◽  
Cost Functions ◽  
Density Estimator ◽  
Monte Carlo Simulation Method ◽  
Commercial Building ◽  
Complementary Method ◽  
The Cost

This article presents the development, simulation and validation of the uncertainty cost functions for a commercial building with climate-dependent controllable loads, located in Florida, USA. For its development, statistical data on the energy consumption of the building in 2016 were used, along with the deployment of kernel density estimator to characterize its probabilistic behavior. For validation of the uncertainty cost functions, the Monte-Carlo simulation method was used to make comparisons between the analytical results and the results obtained by the method. The cost functions found differential errors of less than 1%, compared to the Monte-Carlo simulation method. With this, there is an analytical approach to the uncertainty costs of the building that can be used in the development of optimal energy dispatches, as well as a complementary method for the probabilistic characterization of the stochastic behavior of agents in the electricity sector.

Large Eddy Simulation of Transitional Flow in a Compressor Cascade

2017 ◽  
Author(s):  
Syed Anjum Haider Rizvi ◽  
Joseph Mathew
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Transitional Flow ◽  
Transitional Region ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Large Eddy

At off-design conditions, when the blade Reynolds number is low, a significant part of the blade boundary layer can be transitional. Then, standard RANS models are unable to predict the flows correctly but explicit transition modeling provides some improvement. Since large eddy simulations (LES) are improvements on RANS, the performance of LES was examined by simulating a flow through a linear, compressor cascade for which experimental data are available — specifically at the Reynolds number of 210,000 based on blade chord when transition processes occur over a significant extent of the suction surface. The LES were performed with an explicit filtering approach, applying a low-pass filter to achieve sub-grid-scale modeling. Explicit 8th-order difference formulas were used to obtain high resolution spatial derivative terms. An O-grid was wrapped around the blade with suitable clustering for the boundary layer and regions of large changes along the blade. Turbulent in-flow was provided from a precursor simulation of homogeneous, isotropic turbulence. Two LES and a DNS were performed. The second LES refines the grid in the vicinity of the separation bubble on the suction surface, and along the span. Surface pressure distributions from all simulations agree closely with experiment, thus providing a much better prediction than even transition-sensitive RANS computations. Wall normal profiles of axial velocity and fluctuations also agree closely with experiment. Differences between LES and DNS are small, but the refined grid LES is closer to the DNS almost everywhere. This monotonic convergence, expected of the LES method used, demonstrates its reliability. The pressure surface undergoes transition almost immediately downstream of the leading edge. On the suction surface there are streaks as expected for freestream-turbulence-induced transition, but spots do not appear. Instead, a separating shear layer rolls up and breaks down to turbulence at re-attachment. Both LES capture this process. Skin friction distribution reveals the transition near the re-attachment to occur over an extended region, and subsequent relaxation is slower in the LES. The narrower transition zone in the DNS is indicative of the essential role of smaller scales during transition that should not be neglected in LES. Simulation data also reveal that an assumption of laminar kinetic energy transition models that Reynolds shear stress remains small in the pre-transitional region is supported. The remaining differences in the predictions of such models is thus likely to be the separation-induced transition which preempts the spot formation.

Effect of the Leakage Flows and the Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade

2006 ◽  
Author(s):  
E. de la Rosa Blanco ◽  
H. P. Hodson ◽  
R. Vazquez
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Separation Bubble ◽  
Tangential Velocity ◽  
Low Pressure ◽  
Leakage Flow ◽  
Backward Facing Step ◽  
Surface Separation ◽  
Pressure Surface

This work describes the effect that the injection of leakage flow from a cavity into the mainstream has on the endwall flows and their interaction with a large pressure surface separation bubble in a low-pressure turbine. The effect of a step in hub diameter ahead of the blade row is also simulated. The blade profile under consideration is a typical design of modern low-pressure turbines. The tests are conducted in a low speed linear cascade. These are complemented by numerical simulations. Two different step geometries are investigated, i.e., a backward-facing step and a forward-facing step. The leakage tangential velocity and the leakage mass flow rate are also modified. It was found that the injection of leakage mass flow gives rise to a strengthening of the endwall flows independently of the leakage mass flow rate and the leakage tangential velocity. The experimental results have shown that below a critical value of the leakage tangential velocity, the net mixed-out endwall losses are not significantly altered by a change in the leakage tangential velocity. For these cases, the effect of the leakage mass flow is confined to the wall, as the inlet endwall boundary layer is pushed further away from the wall by the leakage flow. However, for values of the leakage tangential velocity around 100% of the wheelspeed, there is a large increase in losses due to a stronger interaction between the endwall flows and the leakage mass flow. This gives rise to a change in the endwall flows structure. In all cases, the presence of a forward-facing step produces a strengthening of the endwall flows and an increase of the net mixed-out endwall losses when compared with a backward-facing step. This is because of a strong interaction with the pressure surface separation bubble.

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