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 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.

The Influence of Mach Number on the Boundary Layer Development of High-Lift Low Pressure Turbine in Low Reynolds Number

2020 ◽  
Author(s):  
Wenhua Duan ◽  
Jian Liu ◽  
Weiyang Qiao
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Turbine Blade ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Layer Development

Abstract A numerical analysis of the effect of Mach number on the boundary layer development and aerodynamic performance of a high-lift, after loaded low pressure turbine blade is presented in this paper. The turbine blade is designed for the GTF engine and works in a low Reynolds number, high Mach number environment. Three different isentropic exit Mach numbers (0.14, 0.87 and 1.17) are simulated by large eddy simulation method, while the Reynolds number based on the axial chord length of the blade and the exit flow velocity is kept the same (1 × 105). The condition Mais,2 = 0.14 represents the lowspeeed wind tunnel environment which is usually used in the low pressure turbine investigation. The condition Mais,2 = 0.87 represents the design point of the turbine blade. The condition Mais,2 = 1.17 represents the severe environment when the shock wave shows up. A comparison of the boundary layer development is made and the total pressure loss results from the boundary layer is discussed.

The Combined Effects of Surface Roughness with Upstream Wakes on the Boundary Layer Development of an Ultra-High-Lift LPT Blade

2017 ◽  
Vol 34 (1) ◽  
Author(s):  
Sun Shuang ◽  
Lei Zhijun ◽  
Lu Xin’gen ◽  
Zhang Yanfeng ◽  
Zhu Junqiang
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Combined Effects ◽  
High Lift ◽  
Linear Cascade ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Large Measurement ◽  
Lp Turbine ◽  
Layer Development

AbstractThe combined effects of upstream wakes and surface roughness on boundary layer development have been investigated experimentally to improve the performance of ultra-high-lift low-pressure turbine (LPT) blades. The measurement was performed on a linear cascade with an ultra-high-lift LP turbine profile named IET-LPTA with a Zweifel loading coefficient of about 1.4. The wakes were simulated by the moving cylindrical bars upstream of the cascade. The surface roughness was achieved using sandpaper strips which were placed into the slot incised on the blades surfaces. Three types of slots combined with three types of roughness heights formed a large measurement matrix. The roughness with a height of 8.82 μm (1.05×10

Effects of periodic wakes on boundary layer development on an ultra-high-lift low pressure turbine airfoil

2016 ◽  
Vol 231 (1) ◽  
pp. 25-38 ◽  
Author(s):  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Wei Li ◽  
Shuzhen Hu ◽  
Junqiang Zhu
Keyword(s):  
Boundary Layer ◽  
Transition Process ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Turbulent Transition ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Layer Development

The laminar-turbulent transition process in the boundary layer is of significant practical interest because the behavior of this boundary layer largely determines the overall efficiency of a low pressure turbine. This article presents complementary experimental and computational studies of the boundary layer development on an ultra-high-lift low pressure turbine airfoil under periodically unsteady incoming flow conditions. Particular emphasis is placed on the influence of the periodic wake on the laminar-turbulent transition process on the blade suction surface. The measurements were distinctive in that a closely spaced array of hot-film sensors allowed a very detailed examination of the suction surface boundary layer behavior. Measurements were made in a low-speed linear cascade facility at a freestream turbulence intensity level of 1.5%, a reduced frequency of 1.28, a flow coefficient of 0.70, and Reynolds numbers of 50,000 and 100,000, based on the cascade inlet velocity and the airfoil axial chord length. Experimental data were supplemented with numerical predictions from a commercially available Computational Fluid Dynamics code. The wake had a significant influence on the boundary layer of the ultra-high-lift low pressure turbine blade. Both the wake’s high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the ultra-high-lift low pressure turbine airfoil. The upstream unsteady wake segments convecting through the blade passage behaved as a negative jet, with the highest turbulence occurring above the suction surface around the wake center. Transition of the unsteady boundary layer on the blade suction surface was initiated by the wake turbulence. The incoming wakes promoted transition onset upstream, which led to a periodic suppression of the separation bubble. The loss reduction was a compromise between the positive effect of the separation reduction and the negative effect of the larger turbulent-wetted area after reattachment due to the earlier boundary layer transition caused by the unsteady wakes. It appeared that the successful application of ultra-high-lift low pressure turbine blades required additional loss reduction mechanisms other than “simple” wake-blade interaction.

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.

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