The effect of prewhirl on the internal aerodynamics and performance of a mixed flow research centrifugal compressor

The internal three-dimensional steady and time-varying flow through the diffusing elements of a centrifugal impeller were investigated using a moderate scale, subsonic, mixed flow research compressor facility. The characteristics of the test facility which permit the measurement of internal flow conditions throughout the entire research compressor and radial diffuser for various operating conditions are described. Results are presented in the form of graphs and charts to cover a range of mass flow rates with inlet guide vane settings varying from minus 15 degrees to plus 45 degrees. The static pressure distributions in the compressor inlet section and on the impeller and exit diffuser vanes, as well as the overall pressure and temperature rise and mass flow rate, were measured and analyzed at each operating point to determine the overall performance as well as the detailed aerodynamics throughout the compressor

Establishing a Comprehensive Wind Energy Program

This project was directed at establishing a comprehensive wind energy program in Indiana, including both educational and research components. A graduate/undergraduate course ME-514 - Fundamentals of Wind Energy has been established and offered and an interactive prediction of VAWT performance developed. Vertical axis wind turbines for education and research have been acquired, instrumented and installed on the roof top of a building on the Calumet campus and at West Lafayette (Kepner Lab). Computational Fluid Dynamics (CFD) calculations have been performed to simulate these urban wind environments. Also, modal dynamic testing of the West Lafayette VAWT has been performed and a novel horizontal axis design initiated. The 50-meter meteorological tower data obtained at the Purdue Beck Agricultural Research Center have been analyzed and the Purdue Reconfigurable Micro Wind Farm established and simulations directed at the investigation of wind farm configurations initiated. The virtual wind turbine and wind turbine farm simulation in the Visualization Lab has been initiated

Investigation of oscillating cascade aerodynamics by an experimental influence coefficient technique

Fundamental experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate the torsion mode unsteady aerodynamics of a biconvex airfoil cascade at realistic values of the reduced frequency for all interblade phase angles at a specified mean flow condition. In particular, an unsteady aerodynamic influence coefficient technique is developed and utilized in which only one airfoil in the cascade is oscillated at a time and the resulting airfoil surface unsteady pressure distribution measured on one dynamically instrumented airfoil. The unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at a specified interblade phase angle are then determined through a vector summation of these data. These influence coefficient determined oscillation cascade data are correlated with data obtained in this cascade with all airfoils oscillating at several interblade phase angle values. The influence coefficients are then utilized to determine the unsteady aerodynamics of the cascade for all interblade phase angles, with these unique data subsequently correlated with predictions from a linearized unsteady cascade model

Experimental investigation of transonic oscillating cascade aerodynamics

Fundamental experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate the subsonic and transonic aerodynamics of cascaded airfoils executing torsion mode oscillations at realistic values of reduced frequency. In particular, an unsteady aerodynamic influence coefficient technique is developed and utilized. In this technique, only one airfoil in the cascade is oscillated at a time, with the resulting airfoil surface unsteady pressure distribution measured on one dynamically instrumented reference airfoil. The unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at any specified interblade phase angle are then determined through a vector summation of these data. These influence coefficient determined oscillating cascade data were correlated with: (1) data obtained in this cascade with all airfoils oscillating at several interblade phase angle values; and (2) predictions from a classical linearized unsteady cascade model

Wind tunnel wall effects in a linear oscillating cascade

Experiments in a linear oscillating cascade reveal that the wind tunnel walls enclosing the airfoils have, in some cases, a detrimental effect on the oscillating cascade aerodynamics. In a subsonic flow field, biconvex airfoils are driven simultaneously in harmonic, torsion-mode oscillations for a range of interblade phase angle values. It is found that the cascade dynamic periodicity - the airfoil to airfoil variation in unsteady surface pressure - is good for some values of interblade phase angle but poor for others. Correlation of the unsteady pressure data with oscillating flat plate cascade predictions is generally good for conditions where the periodicity is good and poor where the periodicity is poor. Calculations based upon linearized unsteady aerodynamic theory indicate that pressure waves reflected from the wind tunnel walls are responsible for the cases where there is poor periodicity and poor correlation with the predictions

Wave Propagation in a Radial Duct with Mean Swirling Flow

Traditionally, industrial centrifugal compressors have had fewer aeromechanical issues than axial compressors. However, in the development of the next generation high power density industrial compressors, aeromechanical issues are of increasing concern. In particular, a vaned diffuser is frequently being used to increase the compressor efficiency. The resulting impingement of the impeller wakes on the downstream diffuser vanes generates a series of strong acoustic waves. Both experiments [1] and simulations [2] have shown that under certain operating conditions, these acoustic waves generated by the impeller-diffuser vane interactions are strong enough to cause impeller blade failures. To analyze this aeromechanical risk, three primary physical processes are involved: (1) the impeller wakes traveling downstream; (2) the wake interaction with the diffuser vane generating the pressure waves; (3) the pressure waves traveling upstream to excite the impeller. This paper focuses on the development of a mathematical model for the wake and pressure wave propagation in a radial duct with a mean swirling flow, processes 1 and 3. These wave propagation properties are also fundamental to the linearized unsteady aerodynamic analysis of thin airfoil radial cascades required to model the wake-vane interaction, process 2. In subsonic centrifugal compressors, the vaneless space between the impeller and the vaned diffuser is usually in the shape of a thin annulus. To reduce the complexity of the problem, the flow is assumed to be inviscid and two dimensional in the radial and circumferential directions under an isentropic process with no heat transfer. The unsteady flow is modeled as a small perturbation superimposed upon the steady mean flow. Assuming a low Mach number, the mean flow field is found to be irrotational. As shown by Goldstein [3], in a 2-D irrotational mean flow, the pressure wave and vorticity wave, i.e. the wake, are uncoupled. Thus the linearized unsteady Euler equations can be split into two sets of governing equations, one for the pressure waves and the other one for the vorticity waves. To obtain an analytical solution, perturbations are assumed to be harmonic in time and in the circumferential direction, thereby transforming the partial differential governing equations into ordinary differential equations. By applying the boundary condition that the pressure perturbation goes to zero in the limit where the radius is infinite, the perturbation potential associated with the pressure wave is found to be a combination of Hankel functions of the first and second kind. The governing equations for the vorticity wave suggest that the solutions contain both the vorticity wave and an induced hydrodynamic pressure wave due to the non-uniform swirling mean flow. The circumferential perturbation velocity of the vorticity wave is found to decrease with radius whereas the radial perturbation velocity of the vorticity wave increases with radius. The diverging behavior is explained in a similar way as Rayleigh’s criterion for inviscid instability of a basic swirling flow

Unsteady aerodynamics of an oscillating cascade in a compressible flow field

Fundamental experiments were performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics of a cascade of biconvex airfoils executing torsion-mode oscillations at realistic reduced frequencies. Flush-mounted, high-response miniature pressure transducers were used to measure the unsteady airfoil surface pressures. The pressures were measured for three interblade phase angles at two inlet Mach numbers, 0.65 and 0.80, and two incidence angles, 0 and 7 deg. The time-variant pressures were analyzed by means of discrete Fourier transform techniques, and these unique data were then compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle had a major effect on the chordwise distributions of the airfoil surface unsteady pressure, and that reduced frequency, incidence angle, and Mach number had a somewhat less significant effect

Effect of wind tunnel acoustic modes on linear oscillating cascade aerodynamics

The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes which have detrimental effects on the experimental data. Acoustic treatment is proposed to rectify this problem

95-GT-370 CASCADE VORTICAL GUST RESPONSE INCLUDING STEADY LOADING EFFECTS

ABSTRACT A series of expieriments are performed to investigate the effect of steady loading and separated flow on the unsteady vortical gust response of both low and high solidity blade rows, including the effects of airfoil camber. This is accomplished utilizing a unique single stage turbomachine research facility in which the flow is not generated by the blading but rather by an additional fan. This provides the ability to quantify the steady or mean performance of the stator row over a range of steady loading levels both with and without unsteady flow effects. In particular, for a particular mean stator angle-of-attack, the steady and mean aerodynamic performance are determined in a steady flow and also in an unsteady flow generated by a rotor composed of perforated plates at the same mean operating condition. This enables the stator vane row dynamic stall conditions to be identified. The unsteady aerodynamic response of both symmetric and cambered stator vanes configured as low and high solidity stator vane rows is then investigated over a range of mean angle-of-attack values, including attached and separated flows with dynamic stall