Active Fluidic Control of a Nozzle Guide Vane Throat

A simple analytical model is developed for optimum ejector steady-state performance under the assumption that the driver gas mass flow rate exceeds the suction side mass flow rate. This requires the mixing to be at constant pressure and the suction side inlet Mach number to be small. Since the model is formulated in terms of enthalpy, it is applicable to arbitrary motive and suction gases. For purposes of verification, the model is compared with exact numerical results, and with the experimentally determined entrainment ratio used to correct the suction side mass flow rate for changes in temperature or molecular weight. The effect on ejector performance of the pertinent dimensionless parameters is considered. For example, it is shown that the use of a motive fluid with a ratio of specific heats near unity is detrimental to performance. I. Introduction O VER the past few decades there have been many fluid mechanic studies of ejector pumps. Currently, there is renewed interest in ejectors for pumping the subatmospheric effluent of cw chemical lasers,1-4 with primary emphasis on optimized ejector performance. Since an ejector is a pump, performance is in terms of a compression ratio, in particular, the ratio of the exhaust gas stagnation pressure divided by the stagnature pressure of the inlet suction gas. (The suction gas is referred to as the secondary flow; the motive gas is referred to as the primary flow.) Optimum performance is defined here as the largest compression ratio for given primary and secondary flow rates and for a given secondary stagnation pressure. An objective of this work is to derive simple, approximate formulas for the optimum compression ratio in terms of a minimum number of key dimensionless parameters. This approach provides a simple estimate of the maximum possible compression ratio, given the primary and secondary fluids, their stagnation conditions, and their flow rates. Conversely, it does not determine such fundamental characteristics as the transition1 between the mixed and super sonic regimes. Some generality is retained in the choice of parameters for the thermodynamic properties of both primary and secondary gases. This is important for laser application where the-composition of both gases often differs considerably from steam or air. Because of its analytical simplicity, the derivation provides useful insight into the dominant process in an ejector, e.g., a natural consequence of the analysis is an ejector figure of merit. The assumptions underlying the derivation, the derivation itself, and its method of application are presented in Sec. II. The effect on ejector performance of changes in primary gas stagnation enthalpy, ejector nozzle Mach number, etc., are discussed in Sec. III. Of particular interest are the sections which show that a value near unity for the ratio of specific heats of the primary gas leads to a small compression ratio, and that a low subsonic Mach number is required for the secondary inlet flow for optimum compression. To establish the validity of the analysis, a comparison is provided in Sec. Ill with exact computer solutions for a steam and air ejector pumping a chemical laser flow. A simple derivation is also given for the entrainment ratio used by the Heat Exchange In

This paper investigated the film-cooling effectiveness of diffusion slot holes in a turbine nozzle guide vane. The pressure-sensitive paint measurement technique was employed to obtain the film-cooling effectiveness at a density ratio of DR = 1.5. The mainstream Reynolds number based on the axial chord length and the exit velocity was 6 × 105. The mainstream turbulence intensity was approximately 3.7%. Three diffusion slot hole geometries with cross-sectional aspect ratios (ASs) of 2.3, 3.4, and 4.9 were tested and compared with a typical fan-shaped hole. The experiments were performed at three typical hole row locations on the pressure surface (PS) and suction surface (SS). The average blowing ratios varied from M = 0.5 to 2.5. The results showed that throughout the blowing ratio range, on the PS, a substantially higher film-cooling effectiveness than the fan-shaped hole is always obtained from the diffusion slot hole with a large aspect ratio (AS = 4.9); on the SS, the diffusion slot hole with a small AS (AS = 2.3). The influence of hole row positioning is inconsistent for diffusion slot holes with different ASs. The diffusion slot hole is less affected by the PS when the AS is moderate and less affected by the SS when the AS is large. The film-cooling effectiveness of the diffusion slot holes is basically the lowest where the PS has a maximum concave curvature and the highest where the SS has a large favorable pressure gradient.

This paper presents preliminary results of a study performed on bent ejectors having applications in the aerospace industry. The ejectors consisted of a simple round primary nozzle and a bent mixing tube. The effects of bend angles on pumping characteristics were studied. A cold flow wind tunnel was used to provide the primary flow of air at ambient temperature at a maximum mass flow rate of 1.6 kg/sec. Velocity and pressure measurements were taken upstream of the nozzle and at the exit of mixing tube. The study was done with and without swirl in the primary flow. It was observed that swirl in primary flow improved the pumping performance of the bent. CFD analysis was performed using a commercial CFD code and the results were compared with the experiments. It was observed that the bend in the ejector had a significant effect on the pumping performance. The entrainment ratio decreased and then increased with the degree of bend. An ejector with a 45° bend in the geometry had 28% less entrainment ratio than a same size straight ejector. It was found that swirl in the primary flow improves the performance of the bent ejector. A maximum 17% increase in the entrainment ratio was observed with swirl in the case of a 67.5° bent ejector. In both 22.5° and 67.5° bent ejectors the pressure rise was slightly improved by 20° swirl in the primary flow. CFD was generally successful in predicting the trends as observed in the experiment results. CFD predictions of pumping were within ± 7% of the experiments.

Numerical simulations are performed to characterize the secondary injection thrust vector control. For this objective the following measurements were taken: considering the flow to be compressible and turbulent using Realizable k-ε turbulence model accompanied by enhanced wall treatment, the comparison between the CFD results and the experimental results shows a very good agreement. Then a parametric study on injection mass flow rate (changing secondary stagnation pressure) with the same injection location and injection angle is done. The results stated that increasing the injectant mass flow rate lead to shock impingement from opposite wall at secondary stagnation pressure 1.4 of the primary stagnation pressure.

An Outer Planets Probe which retains the charred heatshield during atmospheric descent must deploy a sampling tube through the heatshield to extract atmospheric samples for analysis. Once the sampling tube is deployed, the atmospheric samples ingested must be free of contaminant gases generated by the heatshield. Outgassing products such as methane and water vapor are present in planetary atmospheres and hence, ingestion of such species would result in gas analyzer measurement uncertainties. This paper evaluates the potential for, and design impact of, the extracted atmospheric samples being contaminated by heatshield outgassing products. Flight trajectory data for Jupiter, Saturn and Uranus entries are analyzed to define the conditions resulting in the greatest potential for outgassing products being ingested into the probe's sampling system. An experimental program is defined and described which simulates the key flow field features for a planetary flight in a ground-based test facility. The primary parameters varied in the test include: sampling tube length, injectant mass flow rate and angle of attack. Measured contaminant levels predict the critical sampling tube length for contamination avoidance. Thus, the study demonstrates the compatibility of a retained heatshield concept and high quality atmospheric trace species measurements.

The launch vehicle will experience extreme acoustic environment at lift-off, which will cause the invalidation and destruction of the aerospace equipment, and reducing noise is of great significance for improving launch safety. In this paper, the numerical simulation of gas–liquid two-phase flow and its acoustic field is carried out, and the flow field is simulated by the discrete phase model (DPM), second-order Roe format, Scale-Adaptive Simulation (SAS) and three-dimensional Navier–Stokes. Based on the analysis of the flow field, the acoustic analogy integration method (FW-H) is used to predict the jet noise at the observation position. The influence of the water different injection angles and mass flow rate ratios are studied, and the results show that water injection not only reduces the temperature, velocity and vorticity at the gas–liquid interface, and the temperature at the bottom of the jet deflector, it also significantly reduces the jet noise. The total sound pressure level can be reduced to 6.92 dB by appropriate selection of the water injection angles and water injection mass flow rates. The numerical method established in this paper provides a useful tool for the design and analysis of water injection noise reduction for high-thrust multi-nozzle launch vehicle.

A three-dimensional numerical model of coupled fluid flow and heat transfer in EGS system is investigated. The model considers a single uniform fracture surrounded by a three dimensional low permeable rock matrix. The flow is imposed on a fracture plane, consisting of a doublet system. The primary objectives of this paper are to analyze the effects of injection temperature and mass flow rates on heat extraction performances. The study results showed that for lower injection temperature heat extraction rates from the reservoir are higher. In case of higher injection mass flow rate, energy output increased significantly. However, after thermal breakthrough the energy output drops are seen faster in comparison of lower mass injection case. The faster energy drop with the time are result of the slower heat conduction inside the low permeable rock matrix perpendicular to the fracture. The present model neglected the fracture aperture evolution even though transmissivity reduction is observed. The transmissivity reduction is the results of flow resistance. The flow resistance inside the fracture is increased due to the non-laminar flow and cooling. The combined effect leads to rise the flow impendence of the reservoir. These effects are more for the higher mass at the lower injection temperature.

In this paper an exhaust ejector of boiler based on the principle of injection is mentioned. A three-dimensional numerical simulation on the exhaust ejector of boiler was carried out by using software FLUENT. The effect of the induced pipe geometric parameters (the length and outlet width) on the inner flow field with different conditions was obtained. The simulation results show that some factors, such as velocity distribution, static pressure distribution at the outlet of the pipe caused by the induced pipe geometric variation, are significantly related to injection mass flow rate, and the optimum geometry which can leads to the most injection mass flow rate is h=0.05m, b=0.02m.

This study reports on an experimental and numerical investigation of tip leakage flow control and its effects on the endwall flow structure and stall evolution of a contra-rotating fan. The control method involves the annular injection of high-momentum fluid in the axial direction, upstream of the front rotor. Five-hole probe measurements have been performed at different blade span locations to obtain the hub-to-shroud velocity distribution and also detect stall. Half-annulus transient simulations have been further conducted and validated against experimental tests. Two injection mass flow rates, 1.6% and 3.2% of the main mass flow rate, have been evaluated. Fast Fourier Transform and wavelet transform analyses have been applied to the experimental data. These analyses show that stall disturbances are intensified near the endwall, indicating the tip-critical nature of the studied fan. Under stall conditions, a modal wave in the tip region has been identified, rotating at 40% of the rotor speed. Numerical contours confirm the presence of circumferential disturbances. Also, the results reveal that rotor-2 is responsible for stall initiation. The findings further show that a 3.2% injection has sufficient momentum to eliminate the tip leakage vortex in the endwall flow. With 3.2% tip air injection, the total pressure rise coefficient and the stable operating range increased by 21% and 59%, respectively.

The optimization aims to maximize the film cooling performance while minimizing the corresponding aerodynamic penalty. The cooling performance is assessed using the adiabatic film cooling effectiveness, while the aerodynamic penalty is measured with a mass-averaged total pressure loss coefficient. Two design variables are selected: the coolant-to-mainstream temperature ratio and the coolant-to-mainstream total pressure ratio. Two staggered rows of discrete cylindrical film cooling holes on the suction surface of a turbine vane are considered. A nondominated sorting genetic algorithm (NSGA-II) is coupled with an artificial neural network (ANN) to perform a multiple-objective optimization of the coolant flow parameters on the vane suction surface. Three-dimensional Reynolds-averaged Navier–Stokes (RANS) simulations are employed to construct the ANN network that produces low-fidelity predictions of the objective functions during the optimization. The effect of varying the coolant flow parameters on the adiabatic film cooling effectiveness and the aerodynamic loss is analyzed using the optimization method and RANS simulations. The computational fluid dynamics predictions of the adiabatic film cooling effectiveness and aerodynamic performance are assessed and validated against corresponding experimental measurements. The optimal solutions are reproduced in the experimental facility and the Pareto front is substantiated with experimental data.

Previous experiments demonstrated the effectiveness of using fluidic actuators to throttle the core mass flow through a nozzle guide vane passage. This enables a variable area turbine (VAT) without mechanically moving vanes. The most promising of the fluidic actuators tested was a slot on the suction side of the nozzle guide vane. Using a simple model as a guide, a two-dimensional, RANS, CFD Design of Experiments (DOE) was completed to evaluate the predicted mass flow rate reduction, effectiveness, pressure loss, and exit flow angle for various slot geometries. This DOE was succeeded by the experimental evaluation of seven candidate slot geometries in a small-scale, single nozzle guide vane passage. These candidate slots span the geometric parameters previously described. Experiments showed that when the injection pressure matches the upstream pressure, increasing slot width from 6% to 19% of the geometric throat caused the percentage of primary flow blocked to go from 6.4% to 24.8%. When the slot was pitched from 0° to 60° into the oncoming flow the percentage of primary flow blocked went from 16.0% to 18.2%. Finally, when the slot location was moved away from the computationally determined optimal location the primary flow blocked was reduced. All slot geometries tested had promising effectiveness, generally blocking around twice as much mass flow as they were injecting. Additionally, total pressure loss was seen to strongly correlate with the amount of flow blocked no matter the slot geometry. The trends seen in the simple model and CFD did match the experiments, however CFD appears to have overestimated the performance of the best slot designs.

Automotive paints and coatings: Edited by G. Fettis. VCH, Weinheim, Germany, 1994. 377 pp. ISBN 3-527-28637-3. Price: DM220

Large-eddy simulations (LES) of an under-expanded jet with and without fluidic injection have been carried out. Twelve injection nozzles angled at 60 towards the main jet axis are used for fluidic injection. The effect of two injection mass flow rates along with the amount of the fluidic injection are studied. Longitudinal vortices are generated when the micro jets impinge on the main jet and a thicker shear layer is formed when these vortices diffuse and merge together. Fluidic injection reduces shock-cell size and strength, elongates the potential core, and reduces the turbulence kinetic energy. Increasing the injection mass flow rate brings stronger modifications to the main jet. Shock-associated noise and mixing noise are both reduced, and more reduction is found near the region where shock-associated noise is generated. The magnitude of the high-frequency component is increased near the region where longitudinal vortices are present and this increases with the injection flow rate. The results of the larger injection flow rate are also compared with those of a chevron nozzle. The strength of the longitudinal vortices and the increased shear-layer thickness is comparable for both cases and a similar noise reduction is observed.

Metal additives have positive effects on the flow field such as increasing the temperature and thrust, while this may decrease local gaseous velocity due to inter-phase drag forces on the other hand. An in-house computational solver was developed to study the typical multiphase flow with combustion. The solver relies on Eulerian–Lagrangian model and the two-way coupling approach. Numerical simulations were carried out on an afterburning chamber of a solid-fuel ramjet to study the impact of using aluminum particles as metal additive. For micron-scale aluminum particles, the injection area, initial temperature, diameter and mass flow rate are varied influence factors, while the afterburning chamber and inlet primary high-temperature gases are fixed for all the test cases. It was found that better particle dispersion can result in higher combustion efficiency due to increasing the gas-particle contact area as well as better heat transfer and diffusion. Injecting aluminum particles with higher initial temperature and smaller diameter tend to get ignited faster and then burn more easily, which means releasing more heat in the length-limited flow field. However, the aluminum particle massflow rate has much more complicated comprehensive influence than the changing rules of the adiabatic combustion temperature based on the NASA CEA code.

Considerable heterogeneity is evident when permeability measurements are made on small scales, either in the field or in the laboratory on field samples. Small‐scale permeability measurements have commonly been made by inducing multidimensional gas flow through a sample with various configurations of the conventional surface‐sealing gas minipermeameter. In order to reduce weathering and seal‐quality problems, a new minipermeameter probe was designed for field application within small diameter holes drilled into an outcrop. We briefly describe the small drill hole minipermeameter, while developing in detail the associated data analysis methodology for performing in situ permeability measurements with this new probe. Analysis of field data, which consists of gas injection pressure and mass flow rate, is based on a numerical solution in cylindrical coordinates of the ideal gas flow equation, assuming homogeneous and isotropic conditions over the averaging volume of the measurements. In the following development the semianalytical inverse solution for permeability will be derived for the new small drill hole minipermeameter probe, which varies from that of the conventional surface‐sealing minipermeameter probe only in the choice of the appropriate characteristic length and in the magnitude of the associated geometrical factor.