Effects of Turbulent Boundary Conditions on the Prediction of the Secondary Flow Field in a Linear Compressor Cascade

2016 ◽  
Author(s):  
Peter Busse ◽  
Andreas Krug ◽  
Martin Lange ◽  
Konrad Vogeler ◽  
Ronald Mailach
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Secondary Flow ◽  
Turbulence Model ◽  
Length Scale ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Turbulent Length Scale ◽  
Linear Compressor Cascade ◽  
Secondary Flow Field

For most technical applications, simulations of the Reynolds-Averaged-Navier-Stokes equations has become a standard analysis tool, since it brings a good compromise between computational accuracy and costs. However, turbulence models have to be implemented to close the system of differential equations. To study the effects of turbulent boundary conditions on the prediction of the secondary flow field in a linear compressor cascade with tip clearance, the state of the art RANS solver TRACE in conjunction with Wilcox’ k-ω-turbulence model is used. Besides a stagnation point anomaly prevention, no turbomachinery specific modifications of the turbulence model are applied. Transition is not considered. The current investigations focus on the influence of the imposed turbulent inlet quantities (k0, ω0) on the development of the wall-bounded flow in the cascade. The turbulent kinetic energy k is basically described as a function of the turbulence intensity level measured in an equivalent experimental setup. For the reconstruction of turbulent fluctuations beyond measuring accessibility in the vicinity of the wall, an analytical approach is proposed and validated with DNS data of turbulent flat plate and fully developed channel flows. To identify the influence of different dissipation rates ω on the characteristics of the secondary flow, the free stream turbulent length scale LtFS is varied in four steps ranging from 0.2 up to 5 millimeters. Additionally, the effects of different span-wise length scale distributions across the inlet flow boundary layer are considered.

Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade

2016 ◽  
Author(s):  
Wei Ma ◽  
Feng Gao ◽  
Xavier Ottavy ◽  
Lipeng Lu ◽  
A. J. Wang
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Leading Edge ◽  
Suction Side ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Eddy Simulation ◽  
Linear Compressor Cascade

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.

Numerical Investigations on Effect of Inflow Parameters on Development of Secondary Flow Field for Linear LP Turbine Cascade

2021 ◽  
Author(s):  
Anand P. Darji ◽  
Beena D. Baloni ◽  
Chetan S. Mistry
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Turbulence Model ◽  
Turbulence Intensity ◽  
Numerical Study ◽  
Turbine Cascade ◽  
Wall Flow ◽  
End Wall ◽  
Inflow Conditions ◽  
Secondary Flow Field

Abstract End wall flows contribute the most crucial role in loss generation for axial flow turbine and compressor blades. These losses lead to modify the blade loading and overall performance in terms of stable operating range. Present study aimed to determine the end wall flow streams in a low speed low pressure linear turbine cascade vane using numerical approach. The study includes two sections. The first section includes an attempt to understand different secondary flow streams available at end wall. Location of generation of horseshoe vortex streams and subsequent vortex patterns are identified in the section. The selection of suitable turbulence model among SST (Shear Stress Transport) k–ω and SST γ–θ to identify end wall flow streams is studied in prior in the section. The steady state numerical study is performed using Reynolds Averaged Navier-Stoke’s Equations closed by SST γ–θ turbulence model. The computational results are validated with experimental results available in the literature and are found to be in good agreement. The study is extended for different inflow conditions in later section. The second section includes effect of flow incidence and turbulence intensity on the end wall secondary flow field. Inflow incidences considered for the study are −20°, −10°, 0° (design incidence), +10° and +20°. The inlet turbulence intensities are varied by 1% and 10% for each case. The results revealed different secondary flow patterns at an end wall and found the change in behavior with an inflow conditions. SST γ–θ turbulence model with lower turbulence intensity is more suitable to identify such flow behavior.

An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

2021 ◽  
pp. 1-20
Author(s):  
Liesbeth Konrath ◽  
Dieter Peitsch ◽  
Alexander Heinrich
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Flow Topology ◽  
Linear Compressor ◽  
Near Surface ◽  
Oil Flow ◽  
Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0deg to 5deg for both blades indicates at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down.

Investigations of Three-Dimensional Flow Field Development in an Axial Compressor Cascade

2019 ◽  
Author(s):  
Saeed A. El-Shahat ◽  
Hesham M. El-Batsh ◽  
Ali M. A. Attia ◽  
Guojun Li ◽  
Lei Fu
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Computational Results ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Blade Passage ◽  
Field Development ◽  
Hole Pressure ◽  
Sensor Module ◽  
Linear Compressor Cascade

Abstract This paper presents a complete study about three-dimensional (3-D) flow field development in a linear compressor cascade where flow field in the blade passage has been studied experimentally as well as numerically. In the experimental work, a linear compressor cascade test section was installed in an open loop wind tunnel. The experimental data was acquired for a Reynolds number of 2.98 × 105 based on the blade chord and the inlet flow conditions. The flow field characteristics in blade passage including 3-D flow velocity and velocity magnitude have been measured by using calibrated five and seven-hole pressure probes connected to ATX sensor module data acquisition system (DAQ). To investigate flow development in the blade passage, velocity coefficient through streamwise planes has been calculated from the measured data. The computational fluid dynamics (CFD) study of the flow field was performed to gain a better understanding of the flow features. Present computational study was first validated with previous experimental and numerical work to check mesh accuracy and give confidence for computational results. Then, two turbulence models, Spalart-Allmaras (S-A) and shear stress transport SST (k-ω) were used for the present work. From both parts of study, the flow field development through the cascade have been investigated and compared. Moreover, the received data demonstrated a good agreement between the experimental and computational results. The predicted flow streamlines by numerical calculations showed regions characterized by flow separation and recirculation zones such as corner separation that could be used to enhance the understanding of the loss mechanism in compressor cascades. All measurements taken by the two probes, 5 and 7-hole pressure probes, have been analyzed and compared. The 5-hole pressure probe measurements have showed more agreements with computational results than 7-hole probe. Furthermore S-A turbulence model calculations showed more consistencies with experimental results than SST (k-ω) model.

scholarly journals Calibration of Spalart-Allmaras model for simulation of corner flow separation in linear compressor cascade

2021 ◽  
pp. 1-16
Author(s):  
Kotaro Matsui ◽  
Ethan Perez ◽  
Ryan Kelly ◽  
Naoki Tani ◽  
Aleksandar Jemcov
Keyword(s):  
Mach Number ◽  
Numerical Simulations ◽  
Turbulence Model ◽  
Flow Separation ◽  
Model Parameters ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Calibration Process ◽  
Corner Flow ◽  
Linear Compressor Cascade

This study focuses on the calibration of Spalart--Allmaras turbulence model parameters using the Bayesian inference approach to reproduce experimental measurements of corner flow separation in linear compressor cascade. The quantity of interest selected for the calibration process is the pitchwise distribution of Mach number in the wake of the linear compressor cascade. The model parameters are assumed to be random variables obeying uniform prior probability distributions. Sensitivity analysis is used to rank the importance and select the most influential turbulence model parameters for the calibration process. The sensitivity ranking indicates that two model parameters cb1 and kappa are the most influential random variables resulting in a two--parameter Bayesian calibration process. The likelihood distribution is specified in the form of the Gauss distribution to include the experimental uncertainty. The likelihood distribution is used together with prior distribution to compute posterior probabilities of selected model parameters. The polynomial chaos expansion is employed as a surrogate model to reduce the cost of posterior calculation. Numerical simulations with calibrated turbulence parameters show a significant increase in the accuracy of Mach number profile prediction for separated flows in linear compressor cascade. Numerical simulations also demonstrate that the calibrated set of model coefficients produce accurate predictions of the total pressure and Mach number profiles for the range of incidence angles that were not part of the calibration process.

A Study of Loss Mechanism in a Linear Compressor Cascade at the Corner Stall Condition

2017 ◽  
Author(s):  
Zhiyuan Li ◽  
Juan Du ◽  
Aleksandar Jemcov ◽  
Xavier Ottavy ◽  
Feng Lin
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Main Flow ◽  
Wake Flow ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Flow Loss ◽  
Linear Compressor Cascade ◽  
Profile Loss

The loss-generating mechanism of a linear compressor cascade at the corner stall condition was numerically studied in this paper. The hybrid RANS/LES method was used to perform the high-fidelity simulations. By comparing the results captured by SSTDES, DDES, SAS models with the experimental data, the SSTDES model is proven to be more accurate in capturing the detailed flow structure of the corner stall than the other two models. Taking the turbulence dissipation term of SSTDES model into account, the volumetric entropy generation rate and a new dimensionless local loss coefficient are proposed and used to analyze the loss-generating mechanism in this work. It was found that the main flow loss generated in this cascade could be sorted as the wake flow loss, the profile loss, the secondary flow loss and the endwall loss according to their amounts. The corner separation significantly affects the secondary flow loss, wake flow loss and profile loss in the cascade passage. The mixing between the separated boundary layer flow and the main flow, the shear between a tornado vortex and the main flow are the main sources of the secondary flow loss. The wake flow loss is the largest loss source of the cascade, accounting for 41.8% of the total loss. There are two peaks of the wake flow loss along the spanwise direction near the corner stall region. This phenomenon is related to the appearance of large velocity gradient flows when the main flows and the corner separation flows mix together. The profile loss takes up 40.06 % of the total loss. The profile loss intensity in the corner region is lower than the mid blade span due to the interaction of the boundary layer on the suction side with the corner separation.

An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

2020 ◽  
Author(s):  
Liesbeth Konrath ◽  
Dieter Peitsch ◽  
Alexander Heinrich
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Flow Topology ◽  
Linear Compressor ◽  
Near Surface ◽  
Oil Flow ◽  
Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0° to 5° for both blades indicate at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down, while the rear blade seems unaffected.

Experimental Investigations of Corner Stall in a Linear Compressor Cascade

2011 ◽  
Author(s):  
Wei Ma ◽  
Xavier Ottavy ◽  
Lipeng Lu ◽  
Francis Leboeuf ◽  
Feng Gao
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Three Dimensional ◽  
Suction Side ◽  
Experimental Results ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Inlet Flow ◽  
Linear Compressor ◽  
Linear Compressor Cascade

In order to gain a better knowledge of the mechanisms of corner stall and to calibrate computational-fluid-dynamics (CFD) tools including both Reynolds-averaged Navier-stokes and large eddy simulation, a detailed and accurate experiment of three-dimensional flow field through a linear compressor cascade has been set up. Experimental data were acquired for a Reynolds number of 3.82 × 105 based on blade chord and inlet flow conditions. First, inlet flow conditions were surveyed by hot-wire anemometry in boundary layers. Second, in order to investigate the effects of incidence, measurements then were acquired at five incidences from −2° to 6°. The results included the outlet flow variables of the cascade, measured by a five-hole pressure probe, and static pressures on both blade and endwall surfaces, measured by pressure taps. Third, the flow field details were measured at an incidence angle of 4°. In this configuration the corner stall region was large enough to be investigated, and without two-dimensional (2D) separation at mid-span on the blade suction side near the trailing edge. The velocity field was then measured by 2D Particle Image Velocimetry in cross-sections parallel to the endwall. And the velocity field in the vicinity of the blade suction side was measured with 2D Laser Dropper Anemometry. In order to test the performance of CFD and also to validate the experimental results, a series of numerical simulations were carried out and compared with the experimental results. We thus obtained a set of detailed measurements which constitute an original and complete data base and in good agreement with the published experimental results in literature. These data were also compared with CFD results and showed that the improvements needed in turbulence modeling in order to accurately simulate the three-dimensional separation configuration of corner stall.

Multiscale Partially Averaged Navier Stokes Approach for the Prediction of Flow in Linear Compressor Cascade With Moving Casing

2011 ◽  
Author(s):  
Domenico Borello ◽  
Giovanni Delibra ◽  
Franco Rispoli
Keyword(s):  
Turbulence Models ◽  
Navier Stokes ◽  
Test Case ◽  
Compressor Cascade ◽  
Preliminary Assessment ◽  
Linear Compressor ◽  
Tip Leakage ◽  
Experimental Campaign ◽  
Elliptic Relaxation ◽  
Linear Compressor Cascade

In this paper we present an innovative Partially Averaged Navier Stokes (PANS) approach for the simulation of turbomachinery flows. The elliptic relaxation k-ε-ζ-f model was used as baseline Unsteady Reynolds Averaged Navier Stokes (URANS) model for the derivation of the PANS formulation. The well established T-FlowS unstructured finite volume in-house code was used for the computations. A preliminary assessment of the developed formulation was carried out on a 2D hill flow that represents a very demanding test case for turbulence models. The turbomachinery flow here investigated reproduces the experimental campaign carried out at Virginia Tech on a linear compressor cascade with tip leakage. Their measurements were used for comparisons with numerical results. The predictive capabilities of the model were assessed through the analysis of the flow field. Then an investigation of the blade passage, where experiments were not available, was carried out to detect the main loss sources.

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