Downstream Vane Row Research Articles

Experimental Characterization of Tip Leakage Flow Trajectories in a Multistage Compressor

Fast-response pressure measurements collected in a three-stage axial compressor highlight the development of the rotor tip leakage flow. Data collected from an array of high-frequency-response pressure transducers measure time-resolved static pressure over the rotors at several loading conditions for three tip clearance heights. The influence of surrounding vane rows on the rotor tip leakage flow is investigated by adjusting the position of the vanes with respect to fixed sensor positions. One key result is that the wake from the upstream vane creates a modulation of the leakage flow. However, the upstream propagating potential field from the downstream vane row has no measureable impact on the leakage flow trajectory. In some cases, variations of the leakage flow trajectory angle due to these blade row interactions are greater than the differences due to a doubling of the rotor tip clearance height, an important finding not previously reported in the literature. Differences of the leakage flow trajectory trends with tip clearance are identified for a high loading condition compared to other operating points. Based on these observations, alternate methods are introduced for achieving collapsed leakage flow trajectories with changing tip clearance in two different flow ranges along the speed line.

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

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.

Particle Image Velocimetry Characterization of High-Speed Centrifugal Compressor Impeller-Diffuser Interaction

High-density instantaneous and rotor phase-locked velocity field measurements are made in the centrifugal compressor diffuser vaneless space by means of the particle image velocimetry technique. The technique is challenged in this application by a small length scale and large velocities yielding very small flow time scales and demanding the use of extremely small flow tracking particles. The experiments reveal a detailed picture of the rotor phase-lockedaverageimpellerexitanddiffuserinlet flowfieldasisusefulforunsteady flowmodeling.Strongpassage velocity gradients exist across the vaneless space up to the diffuser vanes, showing that the phase-locked averaged impeller exit flow presents a highly unsteady non-mixed-out velocity field for the downstream vane row. This unsteady vane intake is thus characterized by a strong fluctuation in incidence angle with the passing blade event. Measured time variation in the velocity field indicates a significant time-varying potential field due to incidence fluctuations. Nomenclature Rduct = inlet duct radius r = radius � = radius ratio (diffuser leading-edge radius/impeller tip radius) � = 1 standard deviation

Rotor Wake Variability in a Multistage Compressor

Rotorwakevariability isnot typically accountedforin computational fluid dynamics models,yet small deviations from the modeled average wake could have impacts on performance and forced vibratory response of airfoils. This paper quantifies rotor wake variability, in terms of wake depth and width, for each stage in a three-stage research compressor. Time-resolved flow angle data are acquired with a cross-film sensor at midspan for all three rotor exits for 50 circumferential positions spanning a vane passage. This research focuses on rotor wake variability driven by blade row interactions. The scope of the study includes wake variations caused by blade-to-blade differences, interactions with upstream rotor wakes, and interactions with the potential field of the downstream vane row. The lowest levels of variability are associated with rotor 1. In the downstream rotors, ensemble-averaged revolutions of data show an amplitude modulation caused by interactions with the rotor wakes from the upstream blade rows and, thus, increased levels of blade-to-blade wake variability. The main effect of the downstream vane row is to shift the mean levels of the wake without significantly influencing the wake shape. Nomenclature mc = corrected mass flow rate Nc = corrected rotational speed R = rotor Rec = Reynolds number based on chord length S = stator t = time U = wheel speed V = flow velocity in the absolute reference frame W = flow velocity in the rotating reference frame � = absolute flow angle � = relative flow angle � = adiabatic efficiency � = standard deviation

Three Dimensional Clocking Effects in a One and a Half Stage Transonic Turbine

This paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three-dimensional aerodynamics of the second vane for different clocking positions. To give an overview of the time-averaged flow field, five-hole probe measurements were performed upstream and downstream of the second stator. Furthermore in these planes additional unsteady measurements were carried out with laser Doppler velocimetry in order to record rotor phase-resolved velocity, flow angle, and turbulence distributions at two different clocking positions. In the planes upstream of the second vane, the time-resolved pressure field has been measured by means of a fast response aerodynamic pressure probe. This paper shows that the secondary flows of the second vane are significantly modified by the different clocking positions, in connection with the first vane modulation of the rotor secondary flows. An analysis of the performance of the second vane is also carried out, and a 0.6% variation in the second vane loss coefficient has been recorded among the different clocking positions.

The Effect of Vane Clocking on the Unsteady Flow Field in a One-and-a-Half Stage Transonic Turbine

The current paper presents the results of numerical and experimental clocking investigations performed in a high-pressure transonic turbine with a downstream vane row. The objective was a detailed analysis of shock and wake interactions in such a 1.5-stage machine while clocking the vanes. Therefore, a transient 3D Navier–Stokes calculation was done for two clocking positions, and the three-dimensional results are compared with laser-Doppler-velocimetry measurements at midspan. Additionally, the second vane was equipped with fast response pressure transducers to record the instantaneous surface pressure for 20 different clocking positions at midspan.

Experimental Investigations of Clocking in a One-and-a-Half-Stage Transonic Turbine Using Laser Doppler Velocimetry and a Fast Response Aerodynamic Pressure Probe

The current paper presents experimental clocking investigations of the flow field in midspan in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine). Laser-Doppler-velocimetry measurements were carried out in order to record rotor phase resolved velocity, flow angle, and turbulence distributions upstream and downstream of the second vane row at several different vane-vane positions. Additionally, a fast-response aerodynamic pressure probe was used to get the total pressure distribution downstream of the second vane row for the same positions. Altogether, the measurements were performed for ten different first vane to second vane positions (clocking positions) for measurements downstream of the second vane row and two different clocking positions for measurements upstream of the second vane row. The paper shows that different clocking positions have a significant influence on the flow field downstream of the second vane row. Furthermore, different measurement lines upstream of the second vane row indicate that clocking has nearly no influence on the flow field close to the rotor exit.

Rotor-Generated Vane Row Off-Design Unsteady Aerodynamics Including Dynamic Stall,Part I

Blade row interaction effects on airfoil unsteady aerodynamics are investigated, particularly at off-design operating conditions. The specific problem addressed is off-design unsteady aerodynamics including dynamic stall due to the interaction of rotor-generated wakes with a downstream vane row. This is accomplished by obtaining detailed three-dimensional rotor-stator unsteady aerodynamic blade row interaction data in a low-speed axial-flow research compressor. These detailed data include measurements of the rotor wake generated unsteady aerodynamic forcing function to the downstream stator, the resultant stator vane steady and unsteady aerodynamic response, and particle image velocimetry (PIV) measurements of the time-variant stator midspan vane-to-vane flowfield. The rotor wake-generated forcing function and downstream stator steady and unsteady aerodynamic response data are described, with the time-variant PIV flowfield data described in the companion paper.

Rotor Blade-to-Blade Wake Variability and Effect on Downstream Vane Response

Experiments are performed in a high-speed fan stage to investigate multistage interaction effects on rotor blade-to-blade wake variability and the resulting downstream vane row unsteady aerodynamic response. Multistage effects on the rotor wake are quantified by acquiring data encompassing two complete rotor revolutions at each of several inlet guide vanes clocking positions relative to downstream stationary probes. The resulting downstream vane response data are acquired over a range of steady loading conditions, with both design and off-design operation of the rotor considered. Multistage interactions significantly affect the rotor wake characteristics and lead to the possible generation of rogue wakes. The fundamental periodicity of these interactions is one complete rotor revolution due to the unequal number of blades and vanes in the machine. The rotor wake and resultant vane row unsteady aerodynamic response variability are also quantified. Off-design rotor operation results in wakes with the largest variability, that is, on the order of the average velocity deficit. The variability of the vane response is even more pronounced, as large as 160% of the maximum average unsteady lift over one blade pass period.

Wake Induced Time-Variant Aerodynamics Including Rotor-Stator Axial Spacing Effects

The overall objective of this experimental program was to quantify the effects of rotor-stator axial spacing on the fundamental time-variant aerodynamics relevant to forced response in turbomachinery. This was accomplished in a large-scale, low-speed, single-stage research compressor which permitted two rotor-stator axial spacing ratios representative of those found in advanced design compressors to be investigated. At each value of the axial spacing ratio, the aerodynamically induced fluctuating surface pressure distributions on the downstream vane row, with the primary source of excitation being the upstream rotor wakes, were measured over a wide range of compressor operating conditions. The velocity fluctuations created by the passage of the rotor blades were measured in the nonrotating coordinate system. Data obtained described the variation of the rotor wake with both loading and axial distance from the rotor as parameters. These data also served as a reference in the analysis of the resulting time-variant pressure signals on the vane surfaces.