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.

The Influence of Multimode Transition Initiated by Periodic Wakes on the Profile Loss of a Linear Compressor Cascade

2000 ◽  
Author(s):  
Reinhold Teusch ◽  
Stefan Brunner ◽  
Leonhard Fottner ◽  
Marius Swoboda
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Laminar Separation ◽  
Blade Row ◽  
Linear Compressor Cascade ◽  
Profile Loss ◽  
Undisturbed Flow

This paper presents results of boundary layer and loss measurements in a high speed cascade wind tunnel on a linear compressor cascade under the influence of unsteady, periodic wakes. The wakes of an upstream blade row were simulated by cylindrical bars moved by a belt mechanism upstream of the cascade. Extensive hot-film array, hot-wire and pressure measurements with variation of steady and unsteady inlet flow conditions have been performed for a better understanding of the transition and loss mechanisms on a blade row interacting with wakes. The incoming wakes are inducing early forced transition in the boundary layer followed in time by calmed regions. Due to its higher shear stress level and its fuller velocity profile, the calmed flow is able to suppress laminar separation bubbles and to delay transition in the region with undisturbed flow between wakes, playing a significant role in the loss generation process. At the investigated low Reynolds number, where the measurements for the steady flow case showed a well-developed laminar separation bubble, reductions of profile loss up to 20% were observed for the measured configuration. In the case of the high Reynolds number, where in undisturbed flow only a small separation bubble was detected, a profile loss rise up to 30% was measured. Beside a better understanding of unsteady flow physics the goal of these basic investigations of unsteady transition is to create a wide database for the improvement of transition modeling in unsteady CFD codes.

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.

Unsteady Pressure Investigations of Corner Separated Flow in a Linear Compressor Cascade

2015 ◽  
Author(s):  
Gherardo Zambonini ◽  
Xavier Ottavy
Keyword(s):  
Transfer Functions ◽  
Leading Edge ◽  
Positive Pressure ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Linear Compressor ◽  
Corner Separation ◽  
Unsteady Pressure ◽  
Linear Compressor Cascade ◽  
End Wall

The aim of this work is to present detailed unsteady pressure measurements of three-dimensional flow field in a NACA 65 linear compressor cascade. Chord-based Reynolds number of 382000 and incidence angle of 4 degrees were chosen as target configuration of the rig, which clearly presents the corner separation phenomenon at the juncture of the blade suction side and the end-wall. Concerning the experiments, a characterization of the mean and fluctuating component of wall static pressure on the surface of a specially developed blade is achieved at first. This fluctuating component is investigated utilizing nineteen high sensitivity condenser microphones plugged into blade cavities which have been carefully calibrated. Transfer functions obtained by calibration are exploited to reconstruct the time-dependent pressure signal and finally statistics, conditional ensemble averages, coherence and spectra analyses of fluctuations are presented in order to investigate the unsteady characteristics of the corner separation. High values of root mean square are individuated near the leading edge and in the separation region on the suction surface of the blade. Skewness and kurtosis show an intermittent behavior of the separation onset, which moves upstream and downstream on the suction surface. This intermittency of the separation line is probably linked with the existence of a bimodal behavior of the size of the corner separation. The analyses of coherence and conditional ensemble average between the signals at the leading edge and at the onset of the separation suggest a critical influence of angle and velocity of the incoming end-wall boundary layer on the positive pressure signatures of the shear layer, which characterize the inception of the separation.

scholarly journals Large-eddy simulation of 3-D corner separation in a linear compressor cascade

2015 ◽  
Vol 27 (8) ◽  
pp. 085105 ◽  
Author(s):  
Feng Gao ◽  
Wei Ma ◽  
Gherardo Zambonini ◽  
Jérôme Boudet ◽  
Xavier Ottavy ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Linear Compressor Cascade

scholarly journals Parameter study on numerical simulation of corner separation in LMFA-NACA65 linear compressor cascade

2017 ◽  
Vol 30 (1) ◽  
pp. 15-30 ◽  
Author(s):  
Feng Gao ◽  
Wei Ma ◽  
Jinjing Sun ◽  
Jérôme Boudet ◽  
Xavier Ottavy ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Parameter Study ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Linear Compressor Cascade

Direct Numerical Simulation of By-Pass and Separation-Induced Transition in a Linear Compressor Cascade

2006 ◽  
Author(s):  
Tamer Zaki ◽  
Paul Durbin ◽  
Jan Wissink ◽  
Wolfgang Rodi
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Pressure Gradient ◽  
Surface Boundary ◽  
Mean Flow ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Free Stream Turbulence ◽  
Linear Compressor Cascade

Direct Numerical Simulation (DNS) of flow through a linear compressor cascade with incoming free-stream turbulence was performed. On the pressure side, the boundary layer flow is found to undergo by-pass transition: The incident vortical disturbances trigger the formation of elongated boundary layer perturbation jets (or streaks) with amplitudes on the order of 10% of the mean flow. The inception of turbulent spots, which leads to breakdown, is triggered on the backward perturbation jets (negative u-fluctuations). The turbulent patches spread and finally merge into the downstream, fully turbulent region. The suction surface boundary layer is initially subject to a Favorable Pressure Gradient (FPG), followed by a strong Adverse Pressure Gradient (APG). The FPG suppresses the formation of boundary layer streaks. The result is a stabilized boundary layer that does not undergo transition. Farther downstream, the strong APG causes the laminar boundary layer to separate, which is followed by turbulent reattachment.

Unsteady Boundary Layer Development Due to Wake Passing Effects on a Highly Loaded Linear Compressor Cascade

2004 ◽  
Vol 126 (4) ◽  
pp. 493-500 ◽  
Author(s):  
Lothar Hilgenfeld ◽  
Michael Pfitzner
Keyword(s):  
Boundary Layer ◽  
Measurement Techniques ◽  
Unsteady Boundary Layer ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Boundary Layer Development ◽  
Linear Compressor Cascade ◽  
Wake Passing ◽  
Layer Development ◽  
Highly Loaded

The effects of wake passing on boundary layer development on a highly loaded linear compressor cascade were investigated in detail on the suction side of a compressor blade. The experiments were performed in the High Speed Cascade Wind Tunnel of the Institut fuer Strahlantriebe at Mach and Reynolds numbers representative for real turbomachinery conditions. The experimental data were acquired using different measurement techniques, such as fast-response Kulite sensors, hot-film array and hot-wire measurements. The incoming wakes clearly influence the unsteady boundary layer development. Early forced transition in the boundary layer is followed in time by calmed regions. Large pressure fluctuations detectable in the ensemble averaged Kulite data reveal the existence of coherent structures in the boundary layer. Distinct velocity variations inside the boundary layer are amplified when approaching the blade surface. The time–mean momentum thickness values are reduced compared to the steady ones and therefore clarify the potential for a loss reduction due to wake passing effects.

Sign in / Sign up

Export Citation Format

Share Document