Static Engine Research Articles

Hot Isostatic Pressing Technology for Defence and Space Applications

Hot isostatic pressing (HIP) technology has been established for the development of AISI-304 stainless steel and nickel base superalloy Inconel 718 integral turbine rotors, for liquid propulsion engine of Prithvi missile, and cryoengine of geostationary satellite launch vehicle (GSLV), respectively. Before making the full size rotors, the structure – property relationships in hot isostatic pressed (HIPed) 304 stainless steel and superalloy 718 were established. The HIPed steel and superalloy have shown near 100 per cent theoretical density, homogeneous, and fine grained microstructure. Their mechanical properties were found to be in agreement with those specified for the integral turbine rotors and hence, development of full size near net shaped integral turbine rotors was undertaken. The HIPed steel rotors subjected to the static engine tests have shown a satisfactory performance, and therefore a large number of rotors could be produced to fulfill the requirement of target labs. The HIP technology for the integral turbine rotors was found to be cost effective (about 50 per cent) over the conventional fabrication method which involves forging, machining, and welding of blades to the disk. The processing, structure, and properties of the HIPed 304 stainless steel and superalloy 718 in relation to the performance of integral turbine rotors for missile and space vehicle applications are discussed in this paper. Defence Science Journal, 2012, 62(1), pp.73 -80 , DOI:http://dx.doi.org/10.14429/dsj. 62.372

An exhaust gas recirculation control strategy for passenger car diesel engines using an inverse valve model

In diesel engines, accurate control of the exhaust gas recirculation (EGR) is important because of its effects on the nitrogen oxide and particulate matter emissions. The conventional EGR control system adopts a simple proportional–integral (PI) control algorithm with a lookup-table-based feedforward control and gain scheduling. However, this lookup-table-based control system has limited control performance in transient operations because the lookup tables are obtained from static engine data. The objective of this paper is to improve the control performance of the diesel engine EGR system by using a mathematical model of the EGR path. The proposed EGR control system is composed of PI controller gain scheduling and a feedforward control algorithm based on the mathematical model. The gain-scheduling algorithm provides a PI controller gain based on a sensitivity function that elucidates the relationship between the effective flow area of the EGR valve and the EGR mass flowrate. The feedforward algorithm calculates the EGR valve position based on the inverse model of the EGR valve. The driving cycle test result showed that, compared with the conventional EGR control system, the r.m.s. and maximum values of the target tracking error were reduced by 2.5 per cent and 8.0 per cent respectively.

Design and Development of a Lightweight, Durable, Adjustable Composite Backrest Mounting

ABSTRACT Rigid backrest systems for wheelchairs provide a stable and comfortable base of support to help users maintain good posture while propelling and sitting static. Unfortunately, these backrest systems lack the adjustability necessary to allow users to comfortably perform some tasks, such as dressing; consequently, many users retain their sling-style backrests. We developed a lightweight, durable, adjustable composite (LWDAC) backrest mounting system to address these shortcomings and performed engineering and human subjects testing to evaluate the feasibility of the device. The LWDAC prototype passed the static engineering evaluation, as well as nearly all of the fatigue testing prior to failure of the device. Clinicians (n = 9) and users (n = 8) who evaluated the device in a focus group forum had an overall positive response. The participants agreed the backrest mounting can be operated with one hand and felt comfortable when participants were seated. Wheelchair users were interested in purchasing the backrest, and clinicians indicated they would recommend the LDWAC.

Shape Memory Alloy Based Morphing Aerostructures

In order to continue the current rate of improvements in aircraft performance, aircraft and components which are continuously optimized for all flight conditions, will be needed. Toward this goal morphing-capable, adaptive structures based on shape memory alloy (SMA) technology that enable component and system-level optimization at multiple flight conditions are being developed. This paper reviews five large-scale SMA based technology programs initiated by The Boeing Company. The SAMPSON smart inlet program showed that fully integrated SMA wire bundles could provide a fighter aircraft with a variable engine inlet capability. The reconfigurable rotor blade program demonstrated the ability of highly robust, controlled 55-Nitinol tube actuators to twist a rotor blade in a spin stand test to optimize rotor aerodynamic characteristics. The variable geometry chevron (VGC) program, which was the first use of 60-Nitinol for a major aerospace application, included a flight test and static engine test of the GE90-115B engine fitted with controlled morphing chevrons that reduced noise and increased engine efficiency. The deployable rotor tab employed tube actuators to deploy and retract small fences capable of significantly reducing blade-vortex interaction generated noise on a rotorcraft. Most recently, the variable geometry fan nozzle program has built on the VGC technology to demonstrate improved jet engine performance. Continued maturation of SMA technology is needed in order to develop innovative applications and support their commercialization.

Core Noise Diagnostics of Turbofan Engine Noise UsingCorrelation and Coherence Functions

Cross-correlation and coherence functions are used to look for periodic acoustic components in turbofan engine combustor time histories, to investigate direct and indirect combustion noise source separation based on signal propagation time delays, and to provide information on combustor acoustics. This investigation uses a combustor pressure sensor and a far-field microphone at 130° to study the change in propagation time to the far field of the direct and indirect combustion noise signal using a generalized cross-correlation function. Results are presented as a function of the cutoff frequency of the low-pass filter used to create the generalized cross-correlation function and engine operating condition. The filtering procedure used produces no phase distortion. As the low-pass-filter frequency is decreased, the travel time increases. The indirect combustion noise signal travels more slowly, because the entropy in the combustor moves with the flow, which has a low velocity. The indirect combustion noise signal travels at acoustic velocities after reaching the turbine and being converted into an acoustic signal. The direct combustion noise is always propagating at acoustic velocities. This is in agreement with previous investigations of delay times using a cross-spectrum phase-angle method with unfiltered signals that found indirect combustion noise to be in the 0―200 Hz frequency range and the direct combustion noise to be in the 200-400 Hz frequency range. Similar results obtained using the cross-spectrum phase-angle method with filtered signals are also shown. These results show that the low-pass filtering can be used with the cross-correlation function to separate this type of dependent source and confirm the cross-spectrum results. Although the results are based on a set of static engine tests conducted for one specific dual-spool turbofan engine configuration, they may lead to a better idea about the acoustics in the combustor turbine-tailpipe system and may help develop and validate improved reduced-order physics-based methods for predicting turbofan engine core noise.

The role of nonlinear effects in the propagation of noise from high-power jet aircraft

To address the question of the role of nonlinear effects in the propagation of noise radiated by high-power jet aircraft, extensive measurements were made of the F-22A Raptor during static engine run-ups. Data were acquired at low-, intermediate-, and high-thrust engine settings with microphones located 23-305 m from the aircraft along several angles. Comparisons between the results of a generalized-Burgers-equation-based nonlinear propagation model and the measurements yield favorable agreement, whereas application of a linear propagation model results in spectral predictions that are much too low at high frequencies. The results and analysis show that significant nonlinear propagation effects occur for even intermediate-thrust engine conditions and at angles well away from the peak radiation angle. This suggests that these effects are likely to be common in the propagation of noise radiated by high-power aircraft.

Measurement and Prediction of Noise Propagation from a High-Power Jet Aircraft

Static engine run-up noise measurements have been made on the F-22 Raptor at low and high power settings. At afterburner, the propagation measurements reveal significant evidence of nonlinearity in that there is much greater high-frequency energy than is predicted by linear theory. The measurements have been compared against the results of a nonlinear numerical model based on the generalized Mendousse-Burgers equation. Although the model simplifies the propagation environment in that it neglects ground effects and atmospheric variability, agreement between the measured and nonlinearly predicted spectra is quite favorable. This comparison demonstrates that nonlinear effects can play a significant role in the propagation of high-amplitude noise and that prediction of these effects is possible with this type of numerical model.

Blended wing body structures in multidisciplinary pre-design

The structural analysis of blended wing body (BWB) aircraft configurations is presented in the context of a preliminary, multidisciplinary aircraft design process by means of the aircraft design and optimization program (PrADO) of the Institut of Aircraft Design and Lightweight Structures of the TU Braunschweig. A multidisciplinary process is described that enables parametric creation of detailed finite element models and its loads. Iteratively different flight conditions are trimmed and corresponding pressure distributions calculated by the higher-order subsonic and supersonic panel code HISSS. Each defined loading condition is used for the iterative structural sizing of the primary structure. Based on finite element idealization, a mass estimation of all structural masses is performed. The primary and secondary masses are fed back into the closed overall aircraft optimization loop of PrADO until this iterative procedure shows convergence on calculated aircraft variables (e.g., aircraft masses and static engine thrust). This automated process enables further configuration improvements using manual parametric variations or optimization features of PrADO with an objective function being defined by fuel consumption, aircraft mass, or direct operating costs. Different structural solutions and their integration in the global model are presented for passenger versions of a 700 passenger BWB with special consideration of a pressurized cabin. As an example, structural masses and parametric studies on the influence of the center body rib spacing are presented and compared by weight breakdowns.

On the effect of nonlinear propagation on perceived jet noise levels

Abstract It is common practise to determine the noise impact of aircraft (both civil and military) by using computations, rather than by measurements. Noise impact computations usually make use of noise levels, measured at a relatively small distance from the aircraft, combined with a propagation model. These propagation models are based on linear acoustics and account for effects like atmospheric absorption and lateral attenuation. In the past decades, however, evidence has been found that linear acoustics is inadequate to describe the propagation of high-intensity jet noise. More specifically, it is found that the high frequency part of the spectrum is decaying much slower than predicted by linear acoustics. This behaviour is attributed to nonlinear effects in the propagation. In this paper a method is described that is based on a frequency-domain approach for a broadband time signal. Example calculations are presented, on the simulation of an experiment on an F/A-18E/F aircraft, during a static engine run-up test. Although the measured data are not reproduced accurately in a quantitative sense, the effects attributed to nonlinear propagation are qualitatively the same in both the computed and the measured results: acoustic energy is transferred from the centre frequencies to the higher frequencies, leading to a significantly lower decay of this part of the spectrum. In addition, a parameter study is presented on the effects of nonlinear propagation in terms of overall sound pressure levels. The main conclusions of this study are: • The sound levels at large distances, predicted by a nonlinear propagation method are smaller than those predicted by a linear method. • For the same shape of the spectrum, the difference between ‘nonlinear’ and ‘linear’ results mainly depends on the product of the sound level and the peak frequency at the starting point of the computation. • For typical values of the noise produced by a fighter jet in the near field ( ∼ 10 m ), the nonlinear effect may be of the order of 6 dB. Even if the starting point of the propagation is taken at a more practical distance ( ∼ 50 m ), the nonlinear effect still makes a considerable difference in the outcome of noise impact studies.

Influence of a Conical Axial Injector on Hybrid Rocket Performance

This paper was aimed at analyzing the static engine firings results obtained by means of a hybrid rocket where gaseous oxygen was supplied into axial-symmetric polyethylene cylindrical grains through two different injector configurations: an axial conical subsonic nozzle and a radial injector. The axial injector is considered interesting because of its easy design and the remarkable feature that it produces no significant pressure oscillations for the stabilizing effect due to the hot gas recirculation zone established within the combustion port. To take advantage of its qualities, the assessment of the regression rate variations under the flow field generated by this configuration is required. For the investigated set of operating conditions, the instantaneous regression rates exhibit a time-and-space dependence caused by the impinging jet zone dynamics, while the average regression rates are higher and less mass flux dependent than those achieved with the radial injection motor and expected from the turbulent flow through pipes. A comparison to the data from the radial injector was further drawn in terms of combustion efficiency, fuel consumption profiles, and combustion stability. The radial injector, at the same mass flux and pressure, produces lower regression rates, high pressure oscillations and worse combustion efficiency at the same L*, but more uniform fuel consumption.

Heavy-duty vehicle modelling and longitudinal control

This paper addresses modelling, longitudinal control design and implementation for heavy-duty vehicles (HDVs). The challenging problems here are: (a) an HDV is mass dominant with low power to mass ratio; (b) They possess large actuator delay and actuator saturation. To reduce model mismatch, it is necessary to obtain a nonlinear model which is as simple as the control design method can handle and as complicated as necessary to capture the intrinsic vehicle dynamics. A second order nonlinear vehicle body dynamical model is adopted, which is feedback linearizable. Beside the vehicle dynamics, other main dynamical components along the power-train and drive-train are also modelled, which include turbocharged diesel engine, torque converter, transmission, transmission retarder, pneumatic brake and tyre. The braking system is the most challenging part for control design, which contains three parts: Jake (engine compression) brake, air brake and transmission retarder. The modelling for each is provided. The use of engine braking effect is new complementary to Jake (compression) brake for longitudinal control, which is united with Jake brake in modelling. The control structure can be divided into upper level and lower level. Upper level control uses sliding mode control to generate the desired torque from the desired vehicle acceleration. Lower level control is divided into two branches: (a) engine control: from positive desired torque to desired fuel rate (engine control) using a static engine mapping which basically captures the intrinsic dynamic performance of the turbo-charged diesel engine; (b) brake control: from desired negative torque to generate Jake brake cylinder number to be activated and ON/OFF time periods, applied pneumatic brake pressure and applied voltage of transmission retarder. Test results are also reported.

Quantifying nonlinearity in the propagation of noise from military jet aircraft

Because of the high noise levels radiated by military jet aircraft, it has been hypothesized that nonlinearity influences the propagation of the noise. A numerical model, which accounts for second-order cumulative nonlinearity, atmospheric absorption and dispersion, and geometrical spreading, has been developed to propagate jet noise waveforms. Numerical propagation of recorded waveforms from recent static engine run-up measurements demonstrates significant waveform steepening and an accompanying transfer of spectral energy to high frequencies that agrees well with measured spectra. Furthermore, the measured and nonlinearly predicted waveforms are perceived to be significantly ‘‘louder’’ or ‘‘more annoying’’ than linearly predicted waveforms, despite the fact that standard metrics such as overall sound pressure level (with flat-, A-, and C-weighting) and Stevens Mark-VII perceived loudness show little difference between linearly and nonlinearly predicted spectra. The results of this study demonstrate the need for additional investigations with alternate metrics that more closely relate to perceived annoyance or loudness of high-amplitude jet noise. [Work supported by the Strategic Environmental Research and Development Program.]

Fuzzy logic based intersection delay estimation

A fuzzy logic based delay estimation system is proposed and modelled. Conventional method of delay study involves solving static engineering equations in which only technical factors (traffic demand, roadway geometry, and signal control, etc.) are considered and the affect of nontechnical factors (such as weather or visibility) cannot be analyzed since they do not follow a predefined process. The fuzzy logic based delay estimation combines the complex technical and nontechnical factors and is adaptive to the changing driving environment. The rule base of the delay estimation system is constructed either following a mathematical model or from real-time traffic operational data. Simulation and field test of the fuzzy system have shown that fuzzy logic based modelling is a promising approach to improving intersection delay estimation.

Regression-Rate and Heat-Transfer Correlations for Hybrid Rocket Combustion

A series of static engine Ž rings, thermal pyrolysis experiments, and gas chromatograph/mass spectrometer tests were conducted to investigate the solid-fuel regression rate and heat-transfer behavior in a lab-scale hybrid rocket motor burning hydroxyl terminated polybutadiene/gaseous oxygen. A real-time, X-ray radiography system was used to determine the local, instantaneousregression rates. A dataanalysisprogramwas developedto help correlate the experimental data. The semi-empirical regression-rate correlation showed that, in addition to convection, radiation from soot and variable  uid properties across the boundary layer had signiŽ cant effects on regressionrate behavior. The radiant heat  ux from sootwas relativelymore signiŽ cant under lowmass  ux and low oxidizerto-fuel ratio conditions. Radiation from CO2 , H2O, and CO was quite small compared to convection and soot radiation. The nondimensional regression-rate correlation agreed with the experimental data to within § 3%. Stantonand Nusselt-number correlations were also developed and found to depend on both  ow regime and radiant heat  ux. The regression-rate correlations predicted independent data from both a lab-scale tube burner and the 11-in. (28 cm) JIRAD motor to very reasonable accuracy.

A comparative performance study of vehicle, static engine and synthetically aged autocatalysts using cvs, static engine and synthetic gas rig testing methods

The relative performances of on-road, static engine and furnace aged autocatalysts were measured using three established testing methods. Similar trends were noted between vehicle and static engine evaluation data. Perturbed lambda scan data generated on static engine and synthetic gas rig apparatus also showed good correlation. However, on-road aged catalysts were found to be far more severely deactivated than those subjected to laboratory accelerated ageing.

News and Views

First phase static engine test running of the two RB‐199 Mk.104D engines, which power the EAP (Experimental Aircraft Programme) demonstrator, were successfully completed at British Aerospace Military Aircraft Division Warton, Lancashire.

Experimental Study of Flight Effect on Fan Noise : 2nd, Report, Fan Noise Variations due to Flight Effect

Clarification of fan noise source variation due to a flight effect is important for a turbofan noise reduction and a noise estimation. A fan noise spectral extent and a range of fan operation influenced by the flight effect were studied experimentally using a large turbofan engine and a geodesic 4m diameter semi-sphere inflow control device that can simulate the flight effect on fan noise in static engine tests. The fan noise reduction by the flight effect in a fan approach condition was higher than that in a fan take-off condition, because the fan rotor generates BPF tones by itself near the take-off condition. The highest reduced component in fan noise spectra was a fundamental fan blade passing frequency (BPF) tone, whose reduced level was 20 dB at maximum. Higher harmonic BPF tones and a buzz saw noise were also reduced by the flight effect, but a reduction of broadband noise was not evaluated in the whole range of fan operation.

Correction of fan noise for effects of forward flight

When acoustic measurements are made on a static engine test stand, the data must be corrected for the effects of forward flight to predict correctly the noise characteristics of the engine in flight. A ray tracing approach is used here to relate the static test case to the flight case. The assumptions of isentropic irrotational flow into the fan inlet and a cylindrical shear layer at the fan exhaust lead to slightly different methods for correcting inlet noise and exhaust noise. The forward flight correction method generally involves both an angle and an amplitude correction. The amplitude correction factors for inlet and exhaust noise are the same as that for a dipole and can be as much as 6 dB for a flight Mach number of 0·3. The angle correction for the inlet noise differs from that of the exhaust noise, and both differ from the generally used correction to retarded angle.

Noise Transmission and Control for a Light Twin-Engine Aircraft

One of the dominant source-path combinations for cabin noise in light twin-engine aircraft is propeller noise being transmitted through the fuselage sidewall. This source-path was investigated and candidate sidewall add- on treatments were installed and tested using both an external sound source and the propeller in ground static engine runs. Results indicate that adding either mass or stiffness to the fuselage skin would improve sidewall attenuation and that the honeycomb stiffness treatment provided more improvement at most frequencies than an equal amount of added mass. It is proposed that double-wall construction in conjunction with skin stiffening should provide a good weight-efficient combination for the aircraft studied. NE of the principal source-path combinations of cabin noise in light, twin-engine aircraft is propeller noise transmitted through the fuselage sidewall. Improved methods of controlling this cabin noise are needed to provide a comfortable passenger environment, while at the same time controlling aircraft weight and fuel consumption. Lighter weight noise control methods are needed to replace traditional approaches which have relied largely on relatively heavy damping and mass treatments. A number of approaches have been investigated for reducing cabin noise for this type of aircraft. Flight tests indicated interior noise can be reduced about 3.5 dB(A) by a reduction of engine rpm in an aircraft with variable pitch propellers.1 Design of propeller configurations is being in- vestigated as a means of reducing the noise generated at the source.2 Theoretical prediction methods for sidewall noise transmission have been developed to aid the search for noise- resistant sidewall structures. Theoretical analysis of interior noise transmission has included mechanical analogy models, rigid-stiffener/flexible-panel models, and more complex flexible-stiffener/flexible-panel models. 35 The analyses have been compared with laboratory test data for verification and have been used to examine a number of candidate noise control treatments including variations of skin thickness, stiffener stiffness, and structural damping, and addition of damping, mass, and honeycomb panel stiffening. Previous work has not included evaluation of candidate noise control treatments in an experimental situation using an actual aircraft. Such studies are needed to evaluate and compare candidate treatments, and to guide further development of noise control treatments. The purpose of this paper is to describe an experimental program of evaluation of three noise control treatments. The work is focused on added stiffness in the form of honeycomb panels. Also, two mass treatments are included for comparison. The tests were carried out using a light twin-engine aircraft (Fig. 1). Can- didate treatments were developed using the aircraft with a horn noise source in the laboratory. The performance of the stiffness treatment was verified using ground static runs of the aircraft engines. The laboratory portion of this investigation is described in Ref. 6.

Convective amplification of gas turbine engine internal noise sources

The acoustic field of a noise source is altered when the source is in motion. The change in the acoustic field introduced by the source motion, caused by source alteration and propagation effects, is defined as convective amplification. Previous studies of this phenomenon have been based on analytical models that did not incorporate the physical features necessary for calculation of the convective amplification factor for the internal noise sources of a gas turbine engine, which is required to predict in-flight noise levels from static engine noise measurements. An improved theoretical model was developed. At low frequencies, this model resulted in a convective amplification factor of (1− M 0 cos θ e ) −4, which is identical with the factor established in earlier studies. At high frequencies, however, convective amplification is a function of flight speed, radiation angle, and source geometry.