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B01: Active flow control of stator cascades at periodically-transient boundary conditions

Principal investigators:
Prof. D. Peitsch ()
Prof. R. Liebich ()

WM: Jan Mihalyovics, Dipl.-Ing.  (phone   (030) 314 29481

WM: Tobias Werder, M.Sc.  (
phone
  (030) 314 22941

Summary

At the annular cascade strongly three-dimensional secondary flow develop at the blade-wall-intersection, which is pronounced stronger at the hub than the tip, due to higher loading. To further develop the active flow and closed loop control approaches of the first funding period, this asymmetric flow pattern is simulated in the 2D cascade using a contoured wall while for the annular cascade a 3D blade design is developed to relieve the hub region. In addition to the periodic throttling due to the CVC, the influence of rotor-stator interaction is investigated for active flow control. In addition, trailing edge blowing developed in TP B06 is transferred to the annular cascade and tested in combination with the side wall blowing. Furthermore, experimental and numerical investigations of different concepts of adaptive blade using piezo actuators are validated and verified on the modified 2D-cascade. The results from the 2D-cascade are used to development a design concept of a measuring section for the 3D-test rig to investigate the suitable piezoelectric adaptive blade.

1st Funding period 2012 - 2016

Active flow control in a compressor stator under highly unsteady inflow and outflow conditions

Principal investigators:
Prof. W. Nitsche
Prof. D. Peitsch ()
Dr.-Ing. Inken Peltzer

Summary

The overall efficiency of modern gas turbines is approximately 40% and was raised in small increments only. One approach to increase efficiency currently under investigation includes the modification of the combustion process in the machine. By employing other combustion concepts such as pressure gaining combustion, the efficiency of a gas turbine could be increased.

In the design of a pulsed detonation engine can-annular combustion chambers are used, of which the inlets are closed with a mechanical shutter during combustion to prevent backflow. Closing of the combustion chamber, however, obstructs the flow in the preceding turbomachinery components, mainly on the stator vanes of the last compressor stage.

Fig. 1: Cascade Testrig
Lupe

Within the B01 project we conduct experiments on a periodically unsteady compressor stator flow of the type which would be expected in consequence of pulsed combustion. The experiments are conducted on a highly loaded compressor stator cascade consisting of seven stator blades. The cascade test rig, as it is shown in Figure 1, is operated under low speed conditions at a Reynolds number of Re = 600000. Additionally, a 3D annular wind tunnel will allow for an analysis of the flow at more turbomachinery-like conditions based on the knowledge gained by the 2D cascade.

On this setup a periodic outflow condition is imposed, inducing periodical choking of every passage at Strouhal numbers up to Sr = 0.04. Static pressure measurements on the blade surface and 2D/3C Particle Image Velocimentry (PIV) measurements qualify the baseline flow field under the influence of periodical choking with a focus on the development of the secondary flow structures in the passage and the formation of a laminar separation bubble on the blade. Measurements in the wake of the center blade with a five hole probe are evaluated to determine the phase dependent performance degradation of the stator passage. Figure 2 depicts the highly dynamic flow development in the measurement passage. The disturbance of the neighboring passages induces changes regarding the incidence angle and thereby induce periodic flow separation on the blade’s trailing edge.

Fig. 2: Dynamic Passage Flow (animated)
Lupe

Pulsed air jets emanating from rectangular orifices along the sidewalls of the passages are used for active flow control (AFC) purposes so far. The effect of AFC parameters can be evaluated in terms of reduction of total pressure loss and raise in static pressure across the center passage. It is found that the heavily disturbed uncontrolled flow field stabilizes under the influence of AFC. This implies favorable effect on total pressure loss and static pressure recovery. In future the integration of a blade actuator system will further increase the performance and hence the stability of the compressor. The highly dynamic flow structures regard different AFC parameters for every phase angle. In close cooperation with the B06 project within this collaborative research center 1029 we conduct experiments using different control algorithms.

Fig. 3: Three-dimensional Test Rig
Lupe

In addition to the 2D cascade test rig, rotating bars will be implemented in a three-dimensional test rig producing incoming wakes to the compressor stator. The wake generator is variable in the number of bars and speed to investigate different flow coefficients and blade passing frequencies. Thereby the interaction between the wakes and the periodic choking can be analyzed using independent parameter setting. The AFC concept used in the linear cascade will be adapted to the three-dimensional test rig.

Publications

M. Staats and W. Nitsche and I. Peltzer, 2015. “Active Flow Control on a Highly Loaded Compressor Cascade with Non-Steady Boundary Conditions”. In Active Flow and Combustion Control 2014, King, R., ed., Vol. 127 of Notes on Numerical Fluid Mechanics and Multidisciplinary Design. Springer International Publishing, pp. 23–37.

S. J. Steinberg, M. Staats, W. Nitsche, R. King, 2015. “Comparison of Iterative Learning and Repetitive Control Applied to a Compressor Stator Cascade”. In Active Flow and Combustion Control 2014, King, R., ed., Vol. 127 of Notes on Numerical Fluid Mechanics and Multidisciplinary Design. Springer International Publishing, pp. 39–53.

Submitted:

M. Staats and W. Nitsche, ASME TurboExpo2015 “Active Control of the Corner Separation on a Highly Loaded Compressor Cascade with Periodic non-Steady Boundary Conditions by Means of Fluidic Actuators”

S. J. Steinberg, M. Staats, R. King and W. Nitsche, ASME TurboExpo2015 “ Iterative Learning Active Flow Control Applied to a Compressor Stator Cascade with Periodic Disturbances“

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Speaker

Prof. Dr.-Ing. Dieter Peitsch

Managing director

Steffi Stehr
Room ER 102

Office

Steffi Stehr
sec. ER 2-1
Room 107
Hardenbergstr. 36a
10623 Berlin
+49 (30) 314 23110