scholarly journals High-Speed PIV of shock boundary layer interactions in the transonic buffet flow of a compressor cascade

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Joachim Klinner ◽  
Alexander Hergt ◽  
Sebastian Grund ◽  
Christian E. Willert
Keyword(s):  
High Speed ◽  
Transverse Velocity ◽  
Laser System ◽  
Suction Side ◽  
High Repetition Rate ◽  
Bow Shock ◽  
Compressor Cascade ◽  
Time Resolved ◽  
Set Up ◽  
Transonic Buffet

AbstractThe dynamics of a transonic buffet flow on the suction side of a highly loaded 2-D compressor blade model is investigated at a chord-based Reynolds number of $$1.4 \times 10^6$$ 1.4 × 10 6 and an inlet Mach number of 1.05. Near stall the detached bow shock exhibits pronounced modal shock oscillations at buffet frequencies of $${\omega ^*}=2\pi f c / U_1=2.27$$ ω ∗ = 2 π f c / U 1 = 2.27 which are not related to any structural aeroelastic modes. High-speed PIV at several stations along the chord provides chordwise velocity spectra and wave propagation velocities of shock-induced perturbations. For this purpose, a double-pulse laser system with a high-repetition rate was set up consisting of two combined DPSS lasers. This enables time-resolved PIV using frame straddling at up to 100 kfps and pulse separations down to 800 ns. Synchronized high-speed shadowgraph imaging simultaneously locates the position of the bow shock. Based on cross-correlations between velocity time records at two points and between velocity and shock position, the propagation velocity of the modal perturbations is determined upstream and downstream from the shock. The measured data indicate that feedback occurs between a region immediately downstream of the shock foot and a plane upstream of the shock, up to which transverse velocity disturbances are convected. This observation is contrary to Lee’s model Lee (AIAA J 28(5):942–944, 1990) which describes self-sustained shock-buffet as a consequence of shock–trailing edge interactions. Graphic Abstract

scholarly journals Time-resolved flow field investigation in an industrial centrifugal compressor application involving TR-PIV synchronized with unsteady pressure measurements

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Joachim Klinner ◽  
Melanie Voges ◽  
Michael Schroll ◽  
Alessandro Bassetti ◽  
Christian Willert
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Laser System ◽  
Power Spectra ◽  
Field Investigation ◽  
High Repetition Rate ◽  
Pressure Measurements ◽  
Time Resolved ◽  
Unsteady Pressure ◽  
Unsteady Pressure Measurements

We report on combined velocity and unsteady pressure measurements obtained on an radial compressor with vaneless diffuser and asymmetric volute. Time-resolved PIV recordings were acquired at 26 kHz both upstream of the impeller as well as within the vaneless diffusor at several rotation speeds at clean conditions and prior to the onset of instabilities within the rotor. The velocity data was acquired with a high-repetition rate, double-pulse laser system consisting of two combined DPSS lasers and a high-speed CMOS camera that was synchronized with multi-point unsteady pressure measurements. Details on the facility, the utilized instrumentation and data processing are provided with particular focus on the spectral and coherence analysis. Power spectra obtained from time records of the inlet velocity and unsteady pressure reveal an increase of low-frequency fluctuations below the blade passing frequency and the occurrence of a mode-locked behaviour indicating the presence of rotating instabilities. High levels of correlation between velocity and unsteady pressure signals not only confirm the temporal coherence of the acquired data but also reveal a direct coupling between flow field and pressure signature that is more prominent upstream of the rotor rather than in the diffusor.

Numerical Investigations of Active Flow Control Using Synthetic Jets on a Highly Loaded Compressor Stator Cascade

2010 ◽  
Author(s):  
Christoph Gmelin ◽  
Mathias Steger ◽  
Vincent Zander ◽  
Wolfgang Nitsche ◽  
Frank Thiele ◽  
...  
Keyword(s):  
Separation Bubble ◽  
Active Flow Control ◽  
Suction Side ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Time Resolved ◽  
Laminar Separation ◽  
Zero Net Mass Flux

Time-resolved Reynolds-Averaged Navier-Stokes simulations of a 3D stator compressor cascade are performed. At the design point of the airfoil under investigation, pronounced secondary flow effects are observed. Strong corner vortices emerge from the casing walls and the flow separates from the blade suction side towards the trailing edge. Transition from laminar to turbulent flow occurs within a laminar separation bubble. Using a commercial CFD software, the influence of the spatial resolution is investigated by means of a spanwise coarsening and refinement of the created mesh. Zero net mass flux synthetic jet actuation is used to control the separated regions. The work presents a variation of the temporal discretization and an analysis of the driving parameters of the actuation.

Numerical Investigations of the Efficiency of Circulation Control in a Compressor Stator

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Arne Vorreiter ◽  
Susanne Fischer ◽  
Horst Saathoff ◽  
Rolf Radespiel ◽  
Joerg R. Seume
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Design Method ◽  
Active Flow Control ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Circulation Control ◽  
Compressor Cascade ◽  
First Results ◽  
Active Flow

Airfoil active flow control has been attempted in the past in order to increase the permissible loading of boundary layers in gas turbine components. The present paper presents a stator with active flow control for a high-speed compressor using a Coanda surface near the trailing edge in order to inhibit boundary layer separation. The design intent is to reduce the number of vanes while—in order to ensure a good matching with the downstream rotor—the flow turning angle is kept constant. In a first step, numerical simulations of a linear compressor cascade with circulation control are conducted. The Coanda surface is located behind an injection slot on the airfoil suction side. Small blowing rates lead to a gain in efficiency associated with a rise in static pressure. In a second step, this result is transferred to a four-stage high-speed research compressor, where the circulation control is applied in the first stator. The design method and the first results are based on steady numerical calculations. The analysis of these results shows performance benefits of the concept. For both the cascade and the research compressor, the pressure gain and efficiency are shown as a function of blowing rate and jet power ratio. The comparison is performed based on a dimensionless efficiency, which takes into account the change in power loss.

Numerical Investigations of the Efficiency of Circulation Control in a Compressor Stator

2010 ◽  
Author(s):  
A. Vorreiter ◽  
S. Fischer ◽  
H. Saathoff ◽  
R. Radespiel ◽  
J. R. Seume
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Design Method ◽  
Active Flow Control ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Circulation Control ◽  
Compressor Cascade ◽  
First Results ◽  
Active Flow

Airfoil active flow control has been attempted in the past in order to increase the permissible loading of boundary layers in gas turbine components. The present paper presents a stator with active flow control for a high speed compressor using a Coanda surface near the trailing edge in order to inhibit boundary layer separation. The design intent is to reduce the number of vanes while — in order to ensure a good matching with the downstream rotor — the flow turning angle is kept constant. In a first step, numerical simulations of a linear compressor cascade with circulation control are conducted. The Coanda surface is located behind an injection slot on the airfoil suction side. Small blowing rates lead to a gain in efficiency associated with a rise in static pressure. In a second step, this result is transferred to a 4-stage high speed research compressor, where the circulation control is applied in the first stator. The design method and the first results are based on steady numerical calculations. The analysis of these results shows performance benefits of the concept. For both, the cascade and the research compressor, the pressure gain and efficiency are shown as a function of blowing rate and jet power ratio. The comparison is performed based on a dimensionless efficiency which takes into account the change of power loss.

A New Approach for Compressor Endwall Contouring

2011 ◽  
Author(s):  
Alexander Hergt ◽  
Robert Meyer ◽  
Karsten Liesner ◽  
Eberhard Nicke
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Performance Enhancement ◽  
Cross Flow ◽  
Suction Side ◽  
Significant Loss ◽  
Compressor Cascade ◽  
Boundary Layer Interaction ◽  
Flow Phenomena ◽  
Flow Effects

Against the background of the high development status of modern axial compressors, a further performance enhancement is linked with the extension of the design space in the development process and the concentration on the essential loss mechanisms in the compressor. The performance of a compressor cascade is considerably influenced by secondary flow effects in the near endwall region, since up to 50 percent (for low aspect ratio) of the losses in the bladed channel of a turbomachinery are linked to the endwalls. In this context the application of non-axisymmetric profiled endwalls provides a potential for compressor improvement. The paper presents the detailed experimental and numerical investigation of controlling the endwall cross flow in a compressor cascade. The general approach is based on a boundary layer fence arrangement, whose application on the compressor endwall works as a non-axisymmetric endwall contour. This non-axisymmetric endwall modification constrains the interaction of the endwall cross flow with the suction side boundary layer, thus the onset of the corner separation is delayed and a significant loss reduction of 8 percent is achieved. The experiments were carried out in a linear compressor cascade at the high-speed cascade wind tunnel of the DLR in Berlin at peak efficiency (design point) and off-design of the cascade at Mach number M = 0.67. Furthermore, high fidelity 3D-RANS flow simulations were performed in order to analyze the complex blade and endwall boundary layer interaction. The combined consideration of experimental and numerical flow pattern allows a detailed interpretation and description of the resulting flow phenomena.

Loss determination at a linear cascade under consideration of thermal effects

2020 ◽  
Vol 124 (1280) ◽  
pp. 1592-1614
Author(s):  
S. Aberle-Kern ◽  
R. Niehuis ◽  
T. Ripplinger
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Measurement Data ◽  
Evaluation Procedure ◽  
Special Focus ◽  
Compressor Cascade ◽  
Linear Cascade ◽  
Research Activities ◽  
Set Up ◽  
Profile Loss

ABSTRACTTargeting higher efficiencies and lower fuel consumption of turbomachines, heat transfer and profile loss are research topics of particular interest. In contrast to that, the interaction of both was, so far, rarely investigated, but gains in importance in recent research activities. The profile loss of engine components can be characterised by the airfoil wakes at the blade rows utilising established measurement and evaluation methods for which an adiabatic flow is typically supposed. To enable the investigation of the influence of heat transfer at the blade on the loss characteristics, a novel evaluation procedure was set up. In addition to the pneumatic data, the total temperature in the airfoil wake at a linear cascade was measured by means of a five-hole probe with an integrated thermocouple. For the evaluation and analysis of these data, different definitions of the loss coefficient were investigated and, finally, extended to account for thermal aspects. Furthermore, established techniques to average the local wake data were applied and compared with special focus to their suitability for non-adiabatic cases. Moreover, an extended version of the mixed-out average as defined by Amecke was utilised applying not only a far-reaching consideration of a temperature gradient but also the inclusion of the third spatial dimension to enable the evaluation of field traverses in addition to single wake traverses. These techniques were applied to wake measurement data from a linear compressor cascade gained in a special test set-up in the high-speed cascade wind tunnel for different operating points and different blade temperatures. The suitability of the new methods could be proven, and initial steps of the aerodynamic analysis of the resulting data are presented. Thereby, the acquired techniques turned out as powerful methods for the evaluation of wake traverses on compressor and turbine cascades under non-adiabatic conditions.

Investigation of the second-mode instability at Mach 14 using calibrated schlieren

2018 ◽  
Vol 845 ◽  
Author(s):  
Richard E. Kennedy ◽  
Stuart J. Laurence ◽  
Michael S. Smith ◽  
Eric C. Marineau
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Time Resolved ◽  
Unit Reynolds Number ◽  
Harmonic Frequencies ◽  
Nonlinear Phase ◽  
Second Mode ◽  
Set Up ◽  
Good Agreement

Second-mode wave growth within the hypersonic boundary layer of a slender cone is investigated experimentally using high-speed schlieren visualizations. Experiments were performed in AEDC Tunnel 9 over a range of unit Reynolds number conditions at a Mach number of approximately 14. A thin lens with a known density profile placed within the field of view enables calibration of the schlieren set-up, and the relatively high camera frame rates employed allow for the reconstruction of time-resolved pixel intensities at discrete streamwise locations. The calibration in conjunction with the reconstructed signals enables integrated spatial amplification rates ($N$ factors) to be calculated for each unit Reynolds number condition and compared to $N$ factors computed from both pressure transducer measurements and linear parabolized stability equation (PSE) solutions. Good agreement is observed between $N$ factors computed from the schlieren measurements and those computed from the PSE solutions for the most-amplified second-mode frequencies. The streamwise development of $N$ factors calculated from the schlieren measurements compares favourably to that calculated from the pressure measurements with slight variations in the $N$ factor magnitudes calculated for harmonic frequencies. Finally, a bispectral analysis is carried out to identify nonlinear phase-coupled quadratic interactions present within the boundary layer. Multiple interactions are identified and revealed to be associated with the growth of disturbances at higher harmonic frequencies.

Combination of Active and Passive Flow Control in a High Speed Compressor Cascade

2014 ◽  
Author(s):  
Karsten Liesner ◽  
Robert Meyer
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
High Speed ◽  
Active Flow Control ◽  
Side Wall ◽  
Suction Side ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Compressor Cascade ◽  
Boundary Layer Suction

An experimental study is presented in which passive and active flow control are combined in a way that they complement and support one other. Secondary flow control using boundary layer fences is combined with a boundary layer suction in a compressor cascade at high Mach numbers. Inflow Mach number of 0.67 and Reynolds number (based on chord length) of 560.000 assure realistic conditions. The cascade, equipped with five stator vanes of NACA65 K48 type is used in an ambient condition measurement environment. Pressure measurements form the basis of the experimental investigations, flow visualization is used to obtain insight into the topology of the flow field. The boundary layer fences installed on the suction side of the vanes create a region of low-loss two dimensional flow in the center of the passage. A region of high flow loss is generated at the side wall between wall and BL fence. This region is treated with through-wall boundary layer suction as used in previous investigations. This helps stabilize the flow near the wall and prevent large separated areas. The total pressure loss is reduced remarkably and the outflow becomes more two-dimensional compared to the reference measurement and even compared to the measurement with suction applied without BL fences. The application of boundary layer fences on flow-suction experiments allows obtaining the same loss reduction gains by using lower amounts of suction.

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