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RESEARCH PAPERS

J. Eng. Power. 1976;98(2):137-144. doi:10.1115/1.3446123.

A method of measuring the three-dimensional components of mean velocity and turbulence quantities within a rotating turbomachinery passage is developed through the use of hot wire anemometry techniques. Equations are derived which, when solved simultaneously and in conjunction with the data obtained from the hot wire anemometer measurements, will provide values for the radial, axial and tangential components of mean velocity, turbulence intensity and turbulence stress within the rotating turbomachinery passage. A three-bladed rocket pump inducer model, operating in air, was used in the experimentation. The method is very accurate and provides very useful information on the characteristics of the flow inside rotor passages hitherto unexplored.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):147-157. doi:10.1115/1.3446126.

A premixed laminar propane-air flame burning at the exit of a nozzle, was acoustically excited upstream by a speaker-driver unit. Detailed acoustic measurements were made to show that sound amplification and attenuation can occur over the measurement frequency range from 50 Hz to 350 Hz. The effect of excitation strength and fuel-air ratio was also investigated. Two acoustic phenomena related by forced vortex hydrodynamic behavior have been identified, and were investigated by means of high speed schlieren photographic measurements. The generation of a one-half harmonic of the fundamental frequency was explored and explained in terms of vortex hydrodynamic behavior. The work contributes to the understanding of the origin of noise from acoustically excited combustors.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):159-164. doi:10.1115/1.3446130.

Compressor and turbine blades of aircraft engines are liable to failure from a number of causes. Their subsequent containment within the immediate confines of the engine has long posed problems for the designer aiming for minimum weight designs. To assist the understanding of the dynamics of the containment problem, a series of small scale model tests have been conducted. The particular tests reported, deal with the failure mechanism at the point of impact. A theoretical analysis in support of the results obtained is developed. Fairly good agreement is obtained between tests and theory and the read-across to full scale containment tests indicates that the containment problem is capable of scaling if linear velocities are kept constant. A discontinuity in the behavior of materials with respect to their just contained energy capacity has been identified. While several contributory factors can be suggested, a fully satisfactory explanation is not found.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):165-170. doi:10.1115/1.3446132.

The “time marching” technique is successfully applied to the numerical computation of the nonstationary aerodynamics of a flat plate cascade for compressible flow of either subsonic or supersonic nature. The unsteady perturbation amplitudes of fluid properties are used as the dependent variables so that the computational domain can be reduced to a two-dimensional channel guided by two adjacent blades for any interblade phase angle. A new method of handling the boundary condition is developed in which the order of accuracy for the boundary points will be the same as the interior points. The wake region behind the trailing edge of each blade is treated as a “slip plane” as done in two-dimensional steady state supersonic flow. Results are in good agreement with existing analytical solutions.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):171-181. doi:10.1115/1.3446133.

The effect of residual shaft bow on the unbalance response of a single mass rotor on rigid supports has been examined with a theoretical analysis. The analysis determined the amplitude, phase angle, and peak rotor response speed for various combinations of residual bow and unbalance. For most combinations the phase angle corresponding to the peak rotor response speed was significantly different from the 90 degrees observed in the conventional unbowed rotor. If the residual bow and unbalance were exactly out of phase, the rotor amplitude was zero for a rotor speed equal to the square root of the ratio of residual bow amplitude to unbalance eccentricity. The results of the study suggested a simple method for determining the relative amplitudes of residual bow and unbalance eccentricity based upon the motion of a timing mark on an oscilliscope screen. If the residual bow was less than the unbalance eccentricity, the timing mark moved first in the direction of rotor rotation as the speed is increased and then moved in the opposite direction at a speed less than the critical speed. In the reverse situation, the timing mark moved opposite to the direction of rotation as the speed is increased. At some speed above the critical, it reversed direction. Part II of this paper presents theoretical and experimental results for balancing of a single mass rotor with a residual bow.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):182-187. doi:10.1115/1.3446134.

Three methods of balancing a rotor with a residual shaft bow were presented. Method I balanced the total shaft amplitude to zero at the balance speed. Method II balanced the elastic deflection to zero at the balance speed leaving the residual bow amplitude. Method III balanced the total shaft amplitude to zero at the critical speed without actually operating the rotor at the critical. After balancing by Method I, a large amplitude remained near the critical. Method II balanced the rotor to the residual bow amplitude at all speeds except near the critical where the amplitude is slightly larger than the residual amplitude. The optimum balance resulted from balancing by Method III. In this case, the amplitude was less than or equal to the residual bow amplitude for all speeds except at the critical where the amplitude was zero. Method III required that the critical speed be known prior to balancing. For all three balancing methods, the unbalance influence coefficient must be determined. Two procedures for determining this coefficient were discussed. One was the familiar trial weight influence coefficient method and the other was the direct method which does not require trial weights. Part I of this paper discussed the effect of shaft bow on unbalance response.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):190-198. doi:10.1115/1.3446138.

This paper reports a theoretical study of axial compressor surge. A nonlinear model is developed to predict the transient response of a compression system subsequent to a perturbation from steady operating conditions. It is found that for the system investigated there is an important nondimensional parameter on which this response depends. Whether this parameter is above or below a critical value determines which mode of compressor instability, rotating stall or surge, will be encountered at the stall line. For values above the critical, the system will exhibit the large amplitude oscillatory behavior characteristic of surge; while for values below the critical it will move toward operation in rotating stall, at a substantially reduced flow rate and pressure ratio. Numerical results are presented to show the motion of the compression system operating point during these two basic modes of instability, and a physical explanation is given for the mechanism associated with the generation of surge cycle oscillations.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):199-211. doi:10.1115/1.3446139.

This paper reports an experimental study of axial compressor surge and rotating stall. The experiments were carried out using a three stage axial flow compressor. With the experimental facility the physical parameters of the compression system could be independently varied so that their influence on the transient system behavior can be clearly seen. In addition, a new data analysis procedure has been developed, using a plenum mass balance, which enables the instantaneous compressor mass flow to be accurately calculated. This information is coupled to the unsteady pressure measurements to provide the first detailed quantitative picture of instantaneous compressor operation during both surge and rotating stall transients. The experimental results are compared to a theoretical model of the transient system response. The theoretical criterion for predicting which mode of compression system instability, rotating stall or surge, will occur is in good accord with the data. The basic scaling concepts that have been developed for relating transient data at different corrected speeds and geometrical parameters are also verified. Finally, the model is shown to provide an adequate quantitative description of the motion of the compression system operating point during the transients that occur subsequent to the onset of axial compressor stall.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):218-227. doi:10.1115/1.3446144.

Analytical and experimental investigations of the characteristics of three-dimensional turbulent wakes downstream of a turbomachinery rotor are reported in this paper. An approximate quasi-three-dimensional turbulent wake model for turbomachinery rotor is developed and compared with the cascade and isolated airfoil wake models. The rotor wake model is capable of predicting the decay of mean component of radial and streamwise velocities as a function of rotor geometry, speed of rotation, and the turbulence properties of the flow field. A rotation parameter based on similarity analysis is derived. The velocity profiles in both the radial and cylindrical planes are coupled together. Measurement of mean velocities (Ūn , Ūs , Ūr ), turbulent intensities and stresses (un2, us2, ur2, usun, unur, usur) is carried out using a triple sensor hot wire probe in a stationary system at various axial and radial locations downstream of the rotor. Profiles of mean and turbulent quantities are obtained. Semi-theoretical expressions for the decay rates of the defect in mean velocity, turbulence intensity, and Reynolds stress (maximum values) with distance downstream of the rotor are derived. The experimental data on the rotor wake are compared with that of an isolated airfoil and cascade of airfoils. The investigation suggests that rotor wake decays much faster than the cascade or an isolated airfoil wake.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):229-238. doi:10.1115/1.3446147.

The influence of free stream disturbances on transition is discussed and it is noted that significant regions of laminar flow may exist on axial turbomachine blades despite the high level of disturbance to which they are subjected. A family of surface velocity distributions giving unseparated flow on the suction surface of an axial compressor blade is derived using data from detailed boundary layer measurements on the blading of a single-stage machine. The distributions are broadly similar to those adopted by Wortmann in designing high performance isolated aerofoil sections for operation at much higher Reynolds numbers. The theoretical performance of blades having the specified surface velocity distributions is computed for a wide range of conditions, and the effects of varying Reynolds number and other design parameters are analyzed. The results suggest the possibility of obtaining useful improvements in performance over that of conventional compressor blade sections. The computed performance values show an almost unique relation between the blade losses and the suction surface diffusion ratio. However the correlation of losses with the equivalent diffusion ratio is found to break down at high values of the latter parameter.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):242-246. doi:10.1115/1.3446152.

Experiments are conducted for the noise power and spectra emitted from a gas turbine combustor can exhausting to the atmosphere. The theory of combustion noise is applied to the results to determine the noise generating capability of the flame in the absence of reflecting can surfaces. The results show that for a fixed fuel (JP-4) the noise output is independent of fuel/air ratio for well stabilized can-type flames and heavily dependent on airflow while the spectra are dominated by the can acoustics, primarily through sound absorption by the liner. In an installed configuration the noise output depends heavily on the enclosure acoustics. For well stabilized can-type flames the equivalent unenclosed flame radiates with a thermoacoustic efficiency near 5 × 10−6 , for air-flows of the magnitude used in this program. Scaling rules are presented for installed configurations.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):247-254. doi:10.1115/1.3446153.

When the incoming air flow to a supersonic compressor rotor or cascade has a subsonic axial velocity component, a system of shock and Mach waves originates in the blade leading-edge region, propagates upstream of successive blades, and alters the incident flow conditions. The continuity constraint establishes a unique relationship between the incident Mach number and air flow angle. The shocks are detached and curved with blunt leading edged blades thereby violating the assumptions inherent in the classical simple wave analysis of this flow induction process. The current work employs detached shock models and a rotational flow analysis by the method of characteristics to investigate the effects of airfoil leading edge radius and cascade solidity on the unique incidence values and entrance region total pressure losses. The calculated results are compared to simple wave theory for the entrance region and it is shown that the simple wave assumptions lead to appreciable errors when detached shocks are present in the flow field.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):258-263. doi:10.1115/1.3446157.

It has been commonly accepted that engine stalls during reverser operation are caused by the temperature distortion created by reingested exhaust gasses. Recent studies have shown that compressors respond to instantaneous inlet distortions of a time duration on the order of one engine revolution. This paper describes the results of a test of a high bypass ratio engine during reverse thrust operation which revealed, through the use of high response temperature and pressure measurement, that instantaneous distortions caused by an induced ground vortex were the cause of engine stalls.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):265-272. doi:10.1115/1.3446160.

A correlation method has been developed for predicting the temperature field produced by a single row of closely-spaced jets penetrating into a hot confined crossflow. The correlation procedure predicts the temperature field as a function of the distance downstream of the jet injection plane and pertinent geometric and flow variables. Predicted results are compared with measured data. The tests are selected to represent combinations of geometries or flow variables which give strong verification of the correlations and which are pertinent to gas turbine engine combustor design.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):274-280. doi:10.1115/1.3446163.

The spatial supersonic flow through rotating and stationary annular cascades is analyzed by means of a nonlinear three-dimensional method of characteristics. Three-dimensional corrections for flow quantities referred to a quasi-three-dimensional approximation method are determined depending on geometric and gas dynamical parameters. Characteristic properties of spatial supersonic flow through annular cascades are analyzed, leading to guiding principles for practical design purposes.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):281-289. doi:10.1115/1.3446164.

The current situation of fuel supply, fuel price, noise, and other environmental regulations are reviewed. Some current trends in aero engine design for subsonic transport aircraft are considered and their possible impact on fuel economy, airline economics and the environment are assessed.

Commentary by Dr. Valentin Fuster
J. Eng. Power. 1976;98(2):290-296. doi:10.1115/1.3446165.

The design and manufacturing of dies for forging of turbine and compressor blades represent excellent applications for CAD/CAM. Computer programs have been developed to predict the load, the optimum die design, the best preform position before forging, and the minimum stock volume necessary to fill the die cavity. The predicted forging loads and forging positions agreed well with practical values. For numerical-control machining of forging dies, or of electrodes for Electro Discharge Machining (EDM) of the dies, special-purpose programs have been developed. Thus, the necessary fundamentals are available for an integrated CAD/CAM approach in forging of blades for turbine and compressor applications.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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