Dan Adler

Nozzle Performance Modeling

A polytropic analytical equation system for the internal e ow of nozzles and ducts has been developed by a solution to the combined friction/area change compressible e ow equations. Validation of the system is sought through comparison with experimental data and numerical simulations using FLUENT in the prediction of the performances of two conventional axisymmetric nozzles. Analytical performance coefe cient equations have been developed from the polytropic equation system for this purpose. The predictions with consideration of nozzle divergence angle and roughness are presented for the e rst time. It is demonstrated that the analytical model well matches the experimental data after the throat is fully choked. The numerical and analytical results are compared and discussed. Such an analytical model is extremely useful in bridging the gap between accepted empirical parameters, such as the friction factor and performance factors, and analytical performance modeling. In aircraft nozzle simulations, where empirical data may not be available, this model provides more precise simulation capability especially applicable to modern thrust-vectoring nozzles.

A new method of simultaneous particle sizing and two-component velocity measurement

A new method based on a modified laser interferometric anemometer principle is presented. The new optical system provides a measurement volume of almost constant intensity modulated by fringes and crossed by two dark bands. The particle behaviour inside such a measurement volume is discussed and formulae for the determination of the velocity vector module and its direction are obtained. In the case of large particles a correction for the particle diameter is performed. The particle sizing is based on the analysis of the wave amplitudes of the photomultiplier signal. The accuracy and validation rate are discussed and experimental results obtained with real particulate flow are presented.

Optimizing Subcritical-Flow Thrust-Vectoring of Converging -Diverging Nozzles

Engine thrust vectoring (TV) is a potential technology for military and future civil aircraft in which the Technion— Israel Institute of Technology has made signie cant contributions. This paper provides realistic predictions of steady-state engine performance during steady-state pitch vectoring. The results obtained comprise a required fundamental step for advanced aircraft/TV implementation. This work is a part of the Lockheed Martin yaw‐pitch TV F-16/F-100 research study conducted here at the Jet Laboratory. To this end, a unique TV-engine computer algorithm has been developed that expands the conventional steady-state modeling capabilities of onand off-design as well as the conventional transients (via throttle changes ) to create steady-state and dynamic TV‐engine simulations at various altitudes and Mach numbers. This paper reviews the steady-state performances and the optimization observations initially obtained. The subcritical e ow realm of nozzle performance provides trends aiding in the prediction of thrust benee ts beyond the conventional nozzle design of the F100 model are available as the effective nozzle throat area is allowed to contract through vectoring.

Thrust-vectoring nozzle performance modeling

A polytropic analytical equation system for the internal flow of nozzles, inlets, and ducts has been developed through an analysis of the compressible flow equations including the friction and area change driving potentials. These equations are verified through comparison with experimental data and numerical simulations using FLUENT 5.0. The nozzle performance predictions include consideration of the nozzle divergence and surface roughness. It is demonstrated that the analytical model well matches the experimental data after the throat is fully choked. The numerical and analytical results are compared and discussed. Such an analytical model is extremely useful in bridging the gap between accepted empirical parameters such as the friction factor, performance coefficients, and analytical performance modeling. Furthermore, it provides the first analytical model for thrust-vectoring nozzle performance predictions. In aircraft nozzle simulations where empirical data may not be available, this model provides good simulation capability.

Experimental Investigation of the Stator Wake Propagation Inside the Flow Passages of an Axial Gas Turbine Rotor

The mixing of the wakes created at the exit f rom the Stator vanes was investigated experimentally inside the rotating rotor channels of a cold air turbine. The aspect ratio of the turbine blade was high (1.34). An LDA system for s imultaneous measurement of two velocity components was used. Phase-locked measurements of the relative (to the rotating f rame) velocity vectors, turbulence intensities and the standard deviations of the magnitude and directions of the velocity vectors were carried out on a single cylindrical surface which was far away from the end walls. The measurements were carried out in two relative positions between the stator vanes and the rotor blades. Inlet conditions were adjusted to zero inlet incidence and sub-sonic f low. It was found that the wakes are characterized by high turbulence intensities, high standard deviations and over-turning of the f low direction towards the suction side. During the f low from inlet to outlet, the wakes maintain a high level of standard deviation with a slight increase before the throat and a slight decrease after it. The wake region is gradually spreading downstream a fact which shows that the total turbulent energy is increasing because the main flow generates turbulence. The velocity distribution shows that the f low on the suction side is faster in comparison to the f low near the pressure side, such that the wake on the suction side is convected faster towards the channel exit. This causes the wake to have a distorted bowed shape. The directional over-turning inside the wake region causes a relative motion of the wake f rom the pressure side to the suction side. This motion is slow relative to the main flow. Close to the channel exit separations were detected on the suction side. They occur in the two relative positions of the wake penetration, indicating a possible general phenomena. Nomenclature C = absolute flow speed SD = Standard Deviation TI = Turbulence Intensity U = wheel speed W = relative flow speed X = axial direction y = circumferencial direction WIPN = = Wake Incidence Position Number α = absolute flow angle (relative to U) ß = relative flow angle (relative to U) θ = pitchwise coordinate (tangential angle) in percents Introduction The flow inside an axial gas turbine rotor passages is extremely complicated and is affected by a number of different mechanisms. In recent years, researchers have become increasingly interested in the turbulence structure of the flow in rotors, to achieve better control on the turbulent viscosity field, and thus on the mass and heat transfer rates inside the flow. Among the dominant viscous mechanisms inside the rotor passage are the pulsating stator wakes which cause flow losses, reduced efficiency, and give rise to secondary flows. These wakes probably contribute to an increased heat transfer rate on the pressure side of the blade half way downstream towards the trailing edge. This creates a hot spot on the blade surface, thus shortening the life of the blades. The substantial difficulty of measuring the flow field inside a rotating passage forced most researchers to investigate the wakes at the regions of the inlet and the outlet of the rotor channels, and in the boundary layers on the blades themselves. Dring et al. (1982a), and Joslyn and Dring (1983, 1992a, 1992b) found that the wakes passing on the blades can be detected by strong fluctuations, which get

Thrust-Vectoring Turbofan Jet-Engine Analysis

Engine thrust vectoring (TV) is an emerging new technology for future military and civil aircraft in which the Technion has made significant contributions. Rapidly deflecting engine jets to maneuver the aircraft with or without conventional aerodynamic flight control (CAFC) significantly enhances the flight safety, agility, and combat kill-ratio capabilities of fighter aircraft in the near term and enhances the safety of civil transport jets in the long term. There are yet no realistic predictions of engine dynamic responses to yaw-pitch-roll TV commands in the public domain. Hence, the primary aim of this work is to provide such a first. The results obtained comprise, therefore, a required fundamental step for advanced aircraft/TV implementation. The selection of this work focuses on the Lockheed-Martin TV F-16/F-100 research study conducted at the Technion. A unique TV-engine computer algorithm has been developed that expands the conventional steady-state modeling capabilities of onand off-design as well as the conventional transients (via throttle changes) to create realistic dynamic TV-engine simulations at various altitudes and Mach numbers. This work has been expanded to include predictions for TV in civil aircraft (via a fixed geometry nozzle) under the same conditions. It is concluded that the military TV configuration, as expected, produces no variations in engine performance while providing TV flight control benefits. It is also demonstrated that under the same dynamic conditions, the civil configuration provides an increase in thrust, enhancing the benefits available from TV in the civil domain.

The time response of a hot wire concentration transducer

The time response of a hot wire system, comprising a sampling tube and an analyser, used to measure unsteady concentration fields is investigated. The time lag of a signal and the distortion of the concentration against time profile, both caused by the sampling tube, are calculated theoretically. The theory is verified experimentally and the effects of the system parameters on the profile distortion and time lag are established and discussed. Recommendations for the optimal use of the system in unsteady concentration fields are given.

Analytic and Empirical Analysis of Thrust-Vectoring Engine/Airframe Integration at High AoA

The influence of AoA on the engine behavior along with the resulting effective deflection of the jet are researched here. A previously published polytropic equation system along with an empirically-based analysis are used to evaluate the AoA influence on engine behavior. The engine simulation is of the Pratt & Whitney F-100 as reported previously by the authors. For the thrust vectoring analysis, the nozzle is under an effective nozzle area control allowing for constant thrust across the vectoring range. The in-flight effective deflection angles are calculated using the Sherbaum-Lichtsinder model to provide a robust model of the AoA effects on an in-flight aircraft during constant a vectoring maneuver. Of the two analysis methods used (empirical-based and analytic-based), the empirical-based method is more precise, while the analytic-based model provides realistic results including the total thrust of the engine. The analytic-based method given here along with more concise geometry and operating parameters of the real aircraft provides a realistic base for aircraft performance development and modeling.

Measurement of mean velocities, velocity fluctuations and Reynolds stresses in a turbulent jet with a modified laser interferometric technique

A new optical technique for the measurement of flow velocities with a laser interferometric technique was reported by Menn et al. (1981). Since then the technique has been improved and the authors describe the technique as well as a digital signal processing procedure which has been developed to computer the velocity components from the signal acquired. The method was used to measure velocity fluctuations and Reynolds stresses in an axisymmetric circular air jet. Experimental results are presented and compared with measurements of previous researchers.

Directionally insensitive measurement of pressures in three-dimensional steady flow fields using a hollow porous sphere

The authors describes the flow characteristics of the hollow porous sphere. This information is essential for exact interpretation of the signal and confident use of the hollow porous sphere as a reliable measurement device. Being inexpensive the sphere can be installed in adequate quantities in complex flow systems such as, for example, engine compartments, flow ducts, turbine casings, turbo-impellers, combustion chambers, etc.