An Investigation of the Flow Physics of Vane Clocking Using Unsteady Flow Measurements

2008 ◽  
Author(s):  
Nicole L. Key ◽  
Patrick B. Lawless ◽  
Sanford Fleeter
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Flow Measurements ◽  
Rotor Wake ◽  
Efficiency Condition ◽  
Vane Clocking ◽  
Stage Efficiency

Vane clocking, the circumferential indexing of adjacent vane rows with similar vane counts, has been shown to affect stage efficiency in compressors and turbines. Steady flow measurements acquired in the embedded stage of the Purdue 3-Stage Compressor showed a change in stage efficiency with vane clocking, as discussed in a companion paper. The optimum efficiency condition at design loading occurred when the upstream vane wake impinged on the downstream vane, as had been reported by other vane clocking studies. However, at high loading, the impingement of the upstream vane wake triggered a vane suction side boundary layer separation and resulted in the worst efficiency condition. The objective of this research is to experimentally investigate the maximum and minimum efficiency clocking configurations with unsteady flow measurements to illuminate the flow physics associated with the measured changes in Stage 2 performance. Vane exit unsteady total pressure, velocity, and flow angle measurements were acquired at 50 pitchwise locations spanning one vane passage. Fourier decomposition is used to identify the impact of the upstream rotor wake on the shedding characteristics of the Stator 2 boundary layer and how the placement of the upstream vane wake affects this phenomenon. For the clocking configuration that located the Stator 1 wake at the leading edge of the Stator 2 vane at design loading, it dampened the boundary layer response to the fluctuating incidence associated with rotor wake chopping, leading to a reduction in the size of the structures shed in the Stator 2 vane wake. At the high loading condition, the placement of the Stator 1 wake at the leading edge of Stator 2 triggered a suction side boundary layer separation, resulting in an absence of the upstream rotor blade pass frequency in the spectrum measured in the Stator 2 wake.

scholarly journals Secondary Flow Mixing Losses in a Centrifugal Impeller

1982 ◽  
Author(s):  
M. W. Johnson ◽  
J. Moore
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Centrifugal Impeller ◽  
Cross Sectional ◽  
Flow Measurements ◽  
Layer Separation ◽  
Flow Mixing ◽  
Rotating Impeller

Detailed flow measurements made in a 1-m dia shrouded centrifugal impeller running at 500 rpm are presented. All 3 mutually perpendicular components of relative velocity and rotary stagnation pressures were measured on 5 cross-sectional planes between the inlet and the outlet, using probes which were traversed within the rotating impeller passage. The reduced static pressures were also calculated from these flow measurements. The measurements were made for an impeller flow rate corresponding to approximately zero incidence at the blade leading edges. Shroud boundary layer separation and secondary flow were observed to lead to the formation of a wake in the suction-side/shroud corner region. It is concluded that the turbulent mixing associated with the shroud boundary layer separation and the strength of the secondary flow strongly influence the size and location of the wake respectively.

scholarly journals Influence of Upstream and Downstream Compressor Stators on Rotor Exit Flow Field

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Nicole L. Key
Keyword(s):  
Potential Field ◽  
Computational Models ◽  
Leading Edge ◽  
Suction Side ◽  
Rotor Wake ◽  
Flow Angle ◽  
Absolute Flow ◽  
Measurement Plane ◽  
Vane Clocking

Measurements acquired at the rotor exit plane illuminate the interaction of the rotor with the upstream vane row and the downstream vane row. The relative phase of the upstream and downstream vane rows is adjusted using vane clocking so that the effect of the upstream propagating potential field from the downstream stator can be distinguished from the effects associated with the wakes shed from the upstream stator. Unsteady absolute flow angle information shows that the downstream potential field causes the absolute flow angle to increase in the vicinity of the downstream stator leading edge. The presence of Stator 1 wake is also detected at this measurement plane using unsteady total pressure data. The rotor wakes are measured at different circumferential locations across the vane passage, and the influence of Stator 1 wake on the suction side of the rotor wake is evident. Also, the influence of the downstream stator is detected on the pressure side of the rotor wake for a particular clocking configuration. Understanding the role of the surrounding vane rows on rotor wake development will lead to improved comparison between experimental data and results from computational models.

Secondary Flow Mixing Losses in a Centrifugal Impeller

1983 ◽  
Vol 105 (1) ◽  
pp. 24-32 ◽  
Author(s):  
M. W. Johnson ◽  
J. Moore
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Centrifugal Impeller ◽  
Cross Sectional ◽  
Flow Measurements ◽  
Layer Separation ◽  
Flow Mixing ◽  
Rotating Impeller

Detailed flow measurements made in a 1-m dia shrouded centrifugal impeller running at 500 rpm are presented. All three mutually perpendicular components of relative velocity and rotary stagnation pressures were measured on five cross-sectional planes between the inlet and the outlet, using probes which were traversed within the rotating impeller passage. The reduced static pressures were also calculated from these flow measurements. The measurements were made for an impeller flow rate corresponding to approximately zero incidence at the blade leading edges. Shroud boundary layer separation and secondary flow were observed to lead to the formation of a wake in the suction-side/shroud corner region. It is concluded that the turbulent mixing associated with the shroud boundary layer separation and the strength of the secondary flow strongly influence the size and location of the wake, respectively.

Large Eddy Simulation of Boundary Layer Separation and Reattachment in a LPT Blade at Different Incidence Angles

2015 ◽  
Author(s):  
Yunfei Wang ◽  
Huaping Liu ◽  
Yanping Song ◽  
Fu Chen
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Leading Edge ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Reattachment Point ◽  
Eddy Simulation ◽  
Large Eddy

In order to predict the phenomenon of laminar flow separation, transition and reattachment in a high-lift low-pressure turbine (LPT), a self-developed large eddy simulation program to solve three dimensional compressible N-S equations was used to simulate the flow structures in T106A LPT blade passage. The outlet Mach number is 0.4 and the Reynolds number is 1.1×105 based on the exit isentropic velocity and the axial chord. The distributions of the time-averaged static pressure coefficient, kinetic loss coefficient and wall shear stress on the blade surface at +7.8° incidence angle agree well with the results of experiment and direct numerical simulation (DNS). The locations of laminar separation and reattachment point occur around 83.6% and 97% axial chord respectively. The evolutionary process of spanwise vorticity and large-scale coherent structure near the trailing edge on the suction side in one period indicates that the two-dimensional shear layer is gradually unstable as a result of spanwise fluctuation and Kelvin-Helmholtz (K-H) instability. The boundary layer separates from the suction surface and the hairpin vortex appears in succession, which leads to transition to turbulence. Analysis of the incidence angle effect on the boundary layer separation point as well as separation bubble scale was also performed. A small scale separation bubble exists around the leading edge at positive incidences. As the incidence angle changes from positive to negative, the separation bubble near the leading edge disappears and the boundary layer thickness reduces gradually. The separation point at the rear part of suction side moves downstream, yet the reattachment point barely changes. The Reynolds stress and turbulent kinetic energy profiles change dramatically at zero and positive incidence. This illustrates that the incidence angle has great influence on the development of the boundary layer and the flow field structures.

scholarly journals Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

2021 ◽  
Vol 11 (6) ◽  
pp. 2593
Author(s):  
Yasir Al-Okbi ◽  
Tze Pei Chong ◽  
Oksana Stalnov
Keyword(s):  
Boundary Layer ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Shear Instability ◽  
Vortical Flow ◽  
High Angle ◽  
High Angle Of Attack ◽  
Layer Separation ◽  
Aerodynamic Performances

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively.

Stall Behavior in an Ultra-High-Pressure-Ratio Centrifugal Compressor: Backward-Traveling Rotating Stall

2021 ◽  
pp. 1-51
Author(s):  
Yingjie Zhang ◽  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Ziqing Zhang ◽  
Xu Dong ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Shock Intensity ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Rotating Stall ◽  
High Pressure Ratio ◽  
Ultra High Pressure

Abstract This paper describes the stall mechanism in an ultra-high-pressure-ratio centrifugal compressor. A model comprising all impeller and diffuser blade passages is used to conduct unsteady simulations that trace the onset of instability in the compressor. Backward-traveling rotating stall waves appear at the inlet of the radial diffuser when the compressor is throttled. Six stall cells propagate circumferentially at approximately 0.7% of the impeller rotation speed. The detached shock of the radial diffuser leading edge and the number of stall cells determine the direction of stall propagation, which is opposite to the impeller rotation direction. Dynamic mode decomposition is applied to instantaneous flow fields to extract the flow structure related to the stall mode. This shows that intensive pressure fluctuations concentrate in the diffuser throat as a result of changes in the detached shock intensity. The diffuser passage stall and stall recovery are accompanied by changes in incidence angle and shock wave intensity. When the diffuser passage stalls, the shock-induced boundary-layer separation region near the diffuser vane suction surface gradually expands, increasing the incidence angle and decreasing the shock intensity. The shock is pushed from the diffuser throat toward the diffuser leading edge. When the diffuser passage recovers from stall, the shock wave gradually returns to the diffuser throat, with the incidence angle decreasing and the shock intensity increasing. Once the shock intensity reaches its maximum, the diffuser passage suffers severe shock-induced boundary-layer separation and stalls again.

scholarly journals Measurement of Unsteady Flow and Heat Transfer in a Linear Turbine Cascade

1992 ◽  
Author(s):  
X. Liu ◽  
W. Rodi
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Unsteady Flow ◽  
Boundary Layers ◽  
Suction Side ◽  
Turbine Cascade ◽  
Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Background Turbulence ◽  
Hot Film

A detailed experimental study has been conducted on the wake-induced unsteady flow and heat transfer in a linear turbine cascade. The unsteady wakes with passing frequencies in the range zero to 240 Hz were generated by moving cylinders on a squirrel cage device. The velocity fields in the blade-to-blade flow and in the boundary layers were measured with hot-wire anemometers, the surface pressures with a pressure transducer and the heat transfer coefficients with a glue-on hot film. The results were obtained in ensemble-averaged form so that periodic unsteady processes can be studied. Of particular interest was the transition of the boundary layer. The boundary layer remained laminar on the pressure side in all cases and in the case without wakes also on the suction side. On the latter, the wakes generated by the moving cylinders caused transition, and the beginning of transition moves forward as the cylinder-passing frequency increases. Unlike in the flat-plate study of Liu and Rodi (1991a) the instantaneous boundary layer state does not respond to the passing wakes and therefore does not vary with time. The heat transfer increases under increasing cylinder-passing frequency even in the regions with laminar boundary layers due to the increased background turbulence.

Numerical Study of Wall Influence on Boundary-Layer Transition for Two-Dimensional NACA 16-012 and 4412 Hydrofoil Sections

1990 ◽  
Vol 34 (01) ◽  
pp. 38-47
Author(s):  
R. Latorre ◽  
R. Baubeau
Keyword(s):  
Boundary Layer ◽  
Test Section ◽  
Numerical Study ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Turbulent Separation ◽  
Side Pressure ◽  
Effective Angle

One of the difficulties in hydrofoil model tests is the relatively low Reynolds number of the test piece and the presence of the test section walls. This paper presents the results of systematic calculations of the potential flow field of NA 4412 and NACA 16-012 hydrofoil in a test section with wall-to-chord ratios h/c -1.0. The corresponding boundary-layer calculations using the CERT calculation scheme are presented to show the influence of the nearby walls on shifting the location of the boundary-layer laminar-turbulent separation as well as turbulent separation. By introducing an effective angle of attack, it is possible to obtain close agreement in the calculated and measured suction side pressure distortion as well as the locations of the boundary-layer separation and transition.

Numerical Predictions of Turbine Cascade Secondary Flows and Heat Transfer With Inflow Turbulence

2020 ◽  
Author(s):  
Yousef Kanani ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Leading Edge ◽  
Suction Side ◽  
Lateral Spreading ◽  
Secondary Flows ◽  
Pressure Side ◽  
Initial Flow ◽  
Numerical Predictions ◽  
Inflow Turbulence

Abstract Turbine passage secondary flows are studied for a large rounded leading edge airfoil geometry considered in the experimental investigation of Varty et al. (J. Turbomach. 140(2):021010) using high resolution Large Eddy Simulation (LES). The complex nature of secondary flow formation and evolution are affected by the approach boundary layer characteristics, components of pressure gradients tangent and normal to the passage flow, surface curvature, and inflow turbulence. This paper presents a detailed description of the secondary flows and heat transfer in a linear vane cascade at exit chord Reynolds number of 5 × 105 at low and high inflow turbulence. Initial flow turning at the leading edge of the inlet boundary layer leads to a pair of counter-rotating flow circulation in each half of the cross-plane that drive the evolution of the pressure-side and suction side of the near-wall vortices such as the horseshoe and leading edge corner vortex. The passage vortex for the current large leading-edge vane is formed by the amplification of the initially formed circulation closer to the pressure side (PPC) which strengthens and merges with other vortex systems while moving toward the suction side. The predicted suction surface heat transfer shows good agreement with the measurements and properly captures the augmented heat transfer due to the formation and lateral spreading of the secondary flows towards the vane midspan downstream of the vane passage. Effects of various components of the secondary flows on the endwall and vane heat transfer are discussed in detail.

Unsteady Operation of a Highly Supersonic Organic Rankine Cycle Turbine

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Enrico Rinaldi ◽  
Rene Pecnik ◽  
Piero Colonna
Keyword(s):  
Boundary Layer ◽  
Organic Rankine Cycle ◽  
Suction Side ◽  
Rankine Cycle ◽  
Boundary Layer Separation ◽  
Expansion Ratio ◽  
Ideal Gas ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Shock Interactions

Organic Rankine cycle (ORC) turbogenerators are the most viable option to convert sustainable energy sources in the low-to-medium power output range (from tens of kWe to several MWe). The design of efficient ORC turbines is particularly challenging due to their inherent unsteady nature (high expansion ratios and low speed of sound of organic compounds) and to the fact that the expansion encompasses thermodynamic states in the dense vapor region, where the ideal gas assumption does not hold. This work investigates the unsteady nonideal fluid dynamics and performance of a high expansion ratio ORC turbine by means of detailed Reynolds-averaged Navier–Stokes (RANS) simulations. The complex shock interactions resulting from the supersonic flow (M ≈ 2.8 at the vanes exit) are related to the blade loading, which can fluctuate up to 60% of the time-averaged value. A detailed loss analysis shows that shock-induced boundary layer separation on the suction side of the rotor blades is responsible for most of the losses in the rotor, and that further significant contributions are given by the boundary layer in the diverging part of the stator and by trailing edge losses. Efficiency loss due to unsteady interactions is quantified in 1.4% in absolute percentage points at design rotational speed. Thermophysical properties are found to feature large variations due to temperature even after the strong expansion in the nozzle vanes, thus supporting the use of accurate fluid models in the whole turbine stage.

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