Inlet Guide Vane Research Articles

Non-Linear Design of an IGV-FAN Servo System for Surface Effect Ships

Abstract In this paper, the problem of designing a servo system for Surface Effect Ship applications, based upon a centrifugal fan complemented with an Inlet Guide Vane (IGV), is considered. An IGV-fan system, at constant fan speed, can be regarded as a single-input (the opening of the intake valve) single-output (the delivered air flow) dynamical system, affected by a measurable disturbance (the pressure at the output). The IGV-fan system is characterised by non-trivial non-linearities. For the servo design, a back-box direct method which makes use of I/O measurement only has been used. Such a method provides satisfactory performances when used for the design of the approximate inverse of the IGV-fan system.

L2F anemometry measurements of the inter-row flow field within a transonic axial compressor provided with curved windows

When measurements are performed in high speed, small-scale compressors, the use of curved glass windows is required in order to avoid any mismatch between the measurement window and the casing. However, the glass curvature leads to optical distortions, which hinder acceptable measurements and can even prevent the acquisition of any data. Thus, an original optical assembly, which consists in inserting a simple and inexpensive corrective window between the frontal lens of the anemometer and the shroud window, is proposed. The way of determining the geometric characteristics and the position of this corrective window, which restores very acceptable foci, is presented in the paper. The reliability of this corrective optical assembly is highlighted by comparative measurements in a test case. Using such an optical setting, L2F measurements were realised along a section, downstream of the inlet guide vane (IGV) of a transonic compressor stage. The spatial resolution leads to a good description of the interaction of the wake with the oblique shock emanating from the leading edge of the rotor. A phenomenological study of the wake/shock interaction with a change of frame is realised using the streamwise equation of the transport of vorticity.

Investigation of the Swirling Flow in a Suction Pipe with Inlet Guide Vanes. Experimental Studies of the Swirling Flow in a Suction Pipe of a Centrifugal Compressor.

The swirling flow in a suction pipe with inlet guide vanes was experimentally studied. It was observed that the periodical pressure and velocity oscillations occurred when the guide vane angle was set at middle opening in a pipe in which a disk inserted downstream from the inlet guide vanes. The wall pressure and velocity distribution were measured in various conditions where the inlet guide vane angle and the disk position were changed. It was found that the velocity and wall pressure oscillations were strongly related to each other and that they proceed from upstream to downstream in a pipe with swirling. This phenomenon was considered to be induced by spiral vortices. An operating test showed that the similar phenomenon occurred in a centrifugal compressor suction pipe and a countermeasures to suppress the rotor whirling vibration was valid in which the inlet guide vanes were set adjacent to a compressor impeller.

The Influence of Wake–Wake Interactions on Loss Fluctuations of a Downstream Axial Compressor Blade Row

The interaction between wakes of an adjacent rotor–stator or stator–rotor blade row pair in an axial turbomachine is known to produce regular spatial variations in both the time-mean and unsteady flow fields in a frame relative to the upstream member of the pair. This paper examines the influence of such changes in the free-stream disturbance field on the viscous losses of a following blade row. Hot-wire measurements are carried out downstream of the outlet stator in a 1.5-stage axial compressor having equal blade numbers in the inlet guide vane (IGV) and stator rows. Clocking of the IGV row is used to vary the disturbance field experienced by the stator blades; the influence on stator wake properties is evaluated. The magnitude of periodic fluctuations in ensemble-averaged stator wake thickness is significantly influenced by IGV wake-rotor wake interaction effects. The changes in time-mean stator losses appear marginal.

Centrifugal Compressor Modifications and Their Effect on High-Frequency Pipe Wall Vibration

High-frequency pulsation generated by centrifugal compressors, with pressure wavelengths much smaller than the attached pipe diameter, can cause fatigue failures of the compressor internals, impair compressor performance, and damage the attached compressor piping. There are numerous sources producing pulsation in centrifugal compressors. Some of them are discussed in literature at large (Japikse, 1995; Niese, 1976). NGTL has experienced extreme high-frequency discharge pulsation and pipe wall vibration on many of its radial inlet high-flow centrifugal gas compressor facilities. These pulsations led to several piping attachment failures and compressor internal component failures while the compressor operated within the design envelope. This paper considers severe pulsation conditions at an NGTL compression facility which resulted in unacceptable piping vibration. Significant vibration attenuation was achieved by modifying the compressor (pulsation source) through removal of the diffuser vanes and partial removal of the inlet guide vanes (IGV). Direct comparison of the changes in vibration, pulsation, and performance are made for each of the modifications. The vibration problem, probable causes, options available to address the problem, and the results of implementation are reviewed. The effects of diffuser vane removal on discharge pipe wall vibration as well as changes in compressor performance are described.

Measured Rotor Wake and Potential Forcing Functions, Including Blade Row Interactions

A fundamental experiment is directed at the acquisition and analysis of data dee ning compressible forcing functions generated by a rotor, including interactions with the upstream-generated inlet guide vane (IGV) wakes, for application to wake forcing function models in turbomachine forced-response design systems. The research fan facility consists of an IGV row and a downstream rotor. IGV‐ rotor axial spacing is variable, with the IGV row able to be indexed circumferentially, thereby enabling the rotor wakes to be measured both in the IGV freestream and wakes. At a rotor-relative Mach number of 0.6 unsteady measurements are made of the rotor wake pressure and velocity e elds for two IGV‐ rotor axial spacings and with the rotor wake measured in the IGV freestream and wake regions. The decay characteristics of the rotor blade wakes are compared to empirical correlations. After Fourier decomposition, a vortical‐ potential gust splitting analysis is implemented and applied to the e rst-harmonic data to determine the vortical and potential harmonic wake gust forcing functions both upstream and downstream of the rotor. The potential gust component of the rotor wakes upstream of the rotor is found to be dominated by the e rst-harmonic component with small contributions from the second and third harmonics. Higher harmonics of the vortical gust component of the rotor wakes measured both in and out of the IGV wakes are found to be signie cantly reduced in the IGV wake regions.

Variations in Upstream Vane Loading With Changes in Back Pressure in a Transonic Compressor

Dynamic loading of an inlet guide vane (IGV) in a transonic compressor is characterized by unsteady IGV surface pressures. These pressure data were acquired for two spanwise locations at a 105 percent speed operating condition, which produces supersonic relative Mach numbers over the majority of the rotor blade span. The back pressure of the compressor was varied to determine the effects from such changes. Strong bow shock interaction was evident in both experimental and computational results. Variations in the back pressure have significant influence on the magnitude and phase of the upstream pressure fluctuations. The largest unsteady surface pressure magnitude, 40 kPa, was obtained for the near-stall mass flow condition at 75 percent span and 95 percent chord. Radial variation effects caused by the spanwise variation in relative Mach number were measured. Comparisons to a two-dimensional nonlinear unsteady blade/vane Navier–Stokes analysis show good agreement for the 50 percent span results in terms of IGV unsteady surface pressure. The results of the study indicate that significant nonlinear bow shock influences exist on the IGV trailing edge due to the downstream rotor shock system. [S0889-504X(00)00303-2]

A Study on Performance Inprovement of Cross-Flow Fan by Inlet Guide Vanes.

This paper describes the effect of inlet guide vanes on the performance of a cross-flow fan. The prewhirl in the opposite direction to a rotor rotation is generated by the inlet guide vanes. The pressure coefficient of the cross-flow fan increases with increase of guide vane angle γ, because of the increase of Euler's head in the suction cascade of the rotor. In case of γ=30∼50 degrees both efficiency and pressure coefficient are higher than those of the rotor without guide vanes. Moreover, it is found that a cross-flow fan without guide vanes also has a considerable prewhirl at the rotor inlet.

IGV–Rotor Interaction Analysis in a Transonic Compressor Using the Navier–Stokes Equations

A recently developed, time-accurate multigrid viscous solver has been extended to handle quasi-three-dimensional effects and applied to the first stage of a modern transonic compressor. Interest is focused on the inlet guide vane (IGV)-rotor interaction where strong sources of unsteadiness are to be expected. Several calculations have been performed to predict the stage operating characteristics. Flow structures at various mass flow rates, from choke to near stall, are presented and discussed. Comparisons between unsteady and steady pitch-averaged results are also included in order to obtain indications about the capabilities of steady, multi-row analyses.

Computation of Three-Dimensional Viscous Flow in High Reynolds Number Pump Guide Vane

A three-dimensional Navier-Stokes solver which utilizes a pressure based method is used to compute the incompressible flow field through the inlet guide vane (IGV) of a high Reynolds number pump. The solver has precise control of numerical dissipation through the second and fourth order artificial dissipation terms added to the momentum equations. A low-Reynolds-number form of two-equation turbulence model is used to account for the turbulence effects. Predicted blade surface static pressure distributions are in good agreement with the measurement. The tangential and radial components of the IGV wake velocity, as well as the IGV secondary flow, are predicted well. However, the predicted maximum defect in wake is larger than the measured data. Possible causes for this discrepancy are discussed. The defect in velocity in wakes at midspan is found to decay faster than the perturbation in velocity due to the secondary flow and wake in the tip region.

Aerodynamic Performance of a Transonic Turbine Guide Vane With Trailing Edge Coolant Ejection: Part I—Experimental Approach

Inlet guide vanes (IGV) of high-temperature gas turbines require an effective trailing edge cooling. But this cooling significantly influences the aerodynamic performance caused by the unavoidable thickening of the trailing edge and the interference of the cooling flow with the main flow. As part of a comprehensive research program, an inlet guide vane was designed and manufactured with two different trailing edge shapes. The results from the cascade tests show that the flow behavior upstream of the trailing edge remains unchanged. The homogeneous values downstream show higher turning and higher losses for the cut-back blade, especially in the supersonic range. Additional tests were conducted with carbon dioxide ejection, in order to analyze the mixing process downstream of the cascade.

Study on Surge and Rotating Stall in Axial Compressors. (A Numerical Model and Parametric Study for Multiblade-Row Compressors).

This study investigates the effects of various parameters on the inception and post-stall characteristics of surge and rotating stall in multistage axial compressors, using a numerical model for multiblade-row compressors. The parameters described in this study are the shape of the total pressure loss and deviation angle characteristics, IGV (inlet guide vane) outlet flow angle, inlet flow distortion, and bleeding. It is found that there are two types of rotating stall differing in magnitude, that inlet distortion and the deterioration in compressor performance reduce the inception margin of unstable behavior, and that there is an optimal bleeding that can optimize the inception margin of unstable behavior. The usefulness of the present model is examined through numerical investigations, and the validity of the model is confirmed by comparing predicted results obtained using the model with test results obtained using a single-stage compressor and a 3-stage compressor.

Effect of Radial Gaps between Impeller and Diffuser Vanes on Pressure Fluctuations Downstream of a Diffuser Pump Impeller.

Instantaneous pressures were measured on the casing wall of a guide vane passage and volute casing of a diffuser pump with three different radial gaps between the impeller exit and guide vane inlet. The measured pressure fluctuations were found to decrease with increasing radial gap. Using our method, numerical calculations were performed for the pressure fluctuations, and the calculated pressure fluctuations were found to agree with measured ones. Moreover, the ensemble-averaged pressure data show the effects of the radial gaps on the spatial distribution of unsteady pressures, which causes the rotation of the circumferential pressure mode due to rotor-stator interaction.

Performance Evaluation of Centrifugal Chillers in an Air-Conditioning Plant with The Building Automation System (BAS)

A thermodynamic model with a novel method of describing the performances of centrifugal chillers for air-conditioning is presented. It is based on the first and second laws of thermodynamics which captures the overall entropy change due to non-isentropic compression and expansion of the thermodynamic cycle. The model gives the fundamental relation between the coefficient of performance (COP) and the cooling rates (Qe) for (a) the modulating and (b) the throttling actions of the inlet guide-vanes of the compressor. The usefulness and the accuracy of the model are demonstrated here by analysing the in situ performance of two commercial, installed centrifugal chillers of an air-conditioning plant as well as comparing the available performance data of another chiller in the literature.

Modeling for control of rotating stall

An analytical model for control of rotating stall has been obtained from the basic fluid equations describing the process at inception. The model describes rotating stall as a traveling wave packet, sensed—in spatial components—via the Fourier decomposition of measurements obtained from a circumferential array of evenly distributed sensors (hot wires) upstream of the compressor. A set of “wiggly” inlet guide vanes (IGVs) equally spaced around the compressor annulus constitute the “forced” part of the model. Control is effected by launching waves at appropriate magnitude and phase, synthesized by spatial Fourier synthesis from individual IGV deflections. The effect of the IGV motion on the unsteady fluid process was quantified via identification experiments carried out on a low speed, single-stage axial research compressor. These experiments served to validate the theoretical model and refine key parameters in it. Further validation of the model was provided by the successful implementation of a complex-valued proportional control law, using a combination of first and second harmonic feedback; this resulted in an 18% reduction of stalling mass flow, at essentially the same pressure rise.

Analysis of Wake-Induced Unsteady Flow in Axial Compressors. Radial Variations of Wake Excitation Forces Estimated by Strip Theory.

Wake-induced unsteady flow in an axial compressor is analyzed in a quasi-three-dimensional manner by use of the extended two-dimensional flow analysis method in which the wake decay model developed by the authors is incorporated. In this paper, with the application of the newly developed method to the compressor stages which consist of IGV (Inlet Guide Vane) -rotor-stator blade rows, effects of radial variations in wake characteristics and the axial gaps between two rows on the induced aerodynamic forces are specifically investigated. It is accordingly found that the spanwise phase relationship of incoming wakes has significant effects on the wake excitation forces and moment.

Centrifugal Compressor Inlet Guide Vanes for Increased Surge Margin

This paper describes the results of compressor rig testing with a moderately high specific speed, high inducer Mack number, single-stage centrifugal compressor, with a vaned diffuser, and adjustable inlet guide vanes (IGVs). The results showed that the high-speed surge margin was considerably extended by the regulation of the IGVs, even though the vaned diffuser was apparently operating stalled. Simplified one-dimensional analysis of the impeller and diffuser performances indicated that at inducer tip Mach numbers approaching and exceeding unity, the high-speed surge line was triggered by inducer stall. Also, IGV regulation increased impeller stability. This permitted the diffuser to operate stalled, providing the net compression system stability remained on a negative slope.

Mixing in Axial Flow Compressors: Part II—Measurements in a Single-Stage Compressor and a Duct

This paper follows directly from Part I, which contains not only the description of the facilities and the results for the C106 four-stage compressor, but also the background, list of nomenclature, acknowledgments, and references. The discussion and conclusions for Parts I and II are given here. The single-stage compressor results show the significant effects of inlet guide vane (IGV) wakes on mixing across the stage in the so-called “free-stream” region; in the casing region tip clearance flow is shown to play an important role in mixing. Explanations for these results are given. Investigations were also carried out in a two-dimensional rectangular duct flow to reveal the mixing mechanism in the corner region similar to those formed by blade surfaces and endwalls in a compressor. Turbulent diffusion has been found to be the dominant mechanism in spanwise mixing; anisotropic inhomogeneous turbulent diffusion is mainly responsible for the nonuniform mixing in the corner region. The larger spread of tracer gas in the tangential direction than in the radial direction is mainly caused by the wake dispersion and relative flow motions within the blade wakes as well as secondary flow contributions in the end-wall regions.

Prediction of outlet flow characteristics of centrifugal impellers. (2nd Report, Performance prediction and loss formulae).

In order to predict the flow characteristics around centrifugal impellers for a wide flow-rate range, the outlet flow is analyzed taking reverse flow, wall roughness and boundary layer development into account. An analytical solution of the mass-averaged velocity is obtained in a simple form. Combined with the impeller loss calculation, the prediction method of the overall performance is also presented. The theory is applied to several combinations of impellers and fixed channels of different shapes, and compared with the measurements. The results show that the present theory gives satisfactory results for both the outlet flow characteristics and overall performance curves for wide flow-rate range. It is pointed out that the friction loss in the narrow area from an impeller outlet to a guide vane inlet occupies a large part of the total loss in a low flow-rate range.

Improvements in Performance Characteristics of Single-Stage and Multistage Centrifugal Compressors by Simultaneous Adjustments of Inlet Guide Vanes and Diffuser Vanes

Nowadays, multistage geared centrifugal compressors are most often equipped with three-dimensional impellers and adjustable inlet guide vane cascades, at least upstream of the first stage. Optimum stage efficiencies are made possible by optimum axial in-flow into each stage and freely selectable pinion shaft speeds. Combined with intercooling of the medium, the result is high machine efficiency with good operating ranges. Additional increases in efficiency can be achieved by means of vaned diffusers. Due to the attendant restriction to the working range, this solution is not common in production compressors. Nevertheless, the working range can be distinctly expanded by adjusting the diffuser vanes. In addition, the combination of simultaneous adjustment to inlet guide vanes and diffuser vanes enables an increase in machine efficiency over the entire operating range as compared with regulation using only inlet guide vanes or diffuser vanes. This paper reports on the development of centrifugal compressor stages equipped with vaned diffusers. The impellers have backward-curved blades. Experimental determination of suitable schedules for simultaneous adjustment of both inlet guide vanes and diffuser vanes, depending on the desired performance characteristic, will be dealt with in detail. Furthermore, some examples of the overall performance maps for multistage inter-cooled geared compressors will be shown as a result of combining the performance characteristic curves of the individual stages. The operating ranges and regions of maximum efficiency are optimally matched to the requirements in question by means of suitable adjustment schedules.