Variable Geometry Inlet Research Articles

4D printed NiTi variable-geometry inlet for aero engines

ABSTRACT In modern aerospace engineering, the demand for innovative and adaptable solutions is paramount. This study focuses on enhancing aircraft engine components, specifically variable-geometry inlets, to meet evolving aviation technology requirements. We utilise custom Ni51Ti alloy powder to create 4D printed variable-geometry inlets. A comprehensive examination of thermal history and residual stress reveals differences in the behaviour of NiTi alloys at various points of the 4D printed inlet. After post-treatment, the printed inlet demonstrates stable two-way shape memory effects, undergoing adaptive deformation with temperature changes, mimicking the operational conditions of a commercial aircraft. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) tests confirm that the 4D printed NiTi alloys maintain very stable phase transformation temperatures and two-way shape memory performance. Fluid dynamics simulations further reveal that the variable-geometry inlet design is potentially more efficient in certain operational scenarios with a total pressure recovery factor of 0.9919.

Design and aerodynamic characteristics of variable-geometry hypersonic inlet based on shock wave elimination

To solve the problem that the control of shock wave elimination is weakened under off-design conditions, the design concept of a variable-geometry inlet scheme that combines the variable-geometry cowl (translating and diagonalizing) with regulating shock wave elimination is introduced in this paper. The variable-geometry inlet is designed by the theories of oblique shock wave and isentropic wave as well as the Oswatitsch theory. Regulatory law of the variable-geometry cowl based on shock wave elimination is obtained by the geometric relationships between cowl compression angle, cowl shock wave angle, and optimal control point or range. Numerical simulations are conducted to investigate flow field characteristics, control mechanism, and working performance of the inlet. Results reveal that expansion waves have a significant impact on the cowl shock wave and boundary layer interaction, and flow separation. Furthermore, variable-geometry inlet with translating and diagonalizing cowl based on the regulation of shock wave elimination effectively controls and even completely eliminates the flow separation. In terms of inlet performance, the total pressure loss of the variable-geometry inlet decreases such that the total pressure recovery coefficients of the translating cowl and diagonalizing cowl inlets are increased by maximum values of 3.39 % and 9.97 %, respectively. However, the mass flow coefficient of translating cowl inlet decreases, whereas that of the diagonalizing cowl inlet is equivalent to that of the fixed-geometry inlet. The working range can be widened by changing the internal contract ratio of the inlet through translating or diagonalizing the cowl. The results confirm that the scheme of variable geometry inlet with diagonalizing cowl is practicable and reliable and has important guiding significance and value for inlet design.

Flow Coefficient and Starting Performance Prediction of Variable Geometry Curved Axisymmetric Inlet

With the development of combined cycle engines, it is urgent to estimate more quickly and accurately the flow capture capacity and starting performance of variable geometry inlets over a wide Mach number range. Based on the flow field and parameter fitting, two prediction methods for the curved axisymmetric inlet with lip translation scheme have been proposed. The method based on the flow field of the reference inlet is more efficient than the parameters-based prediction method, as it can accurately predict the lip translation distance and the corresponding flow coefficient over the entire working range of the inlet without additional numerical calculations. Moreover, the starting Mach number is accurately predicted by the fitting method based on the throat Mach number of the reference inlet, with a relative error of only 0.95% compared to the numerical simulation. The flow coefficient-based method is simple and accurate for predicting lip translation distances with a known starting Mach number, with a relative error of only 1.65% compared to numerical simulations. The prediction approaches can overcome the drawbacks of the standard iterative algorithms and significantly enhance computational accuracy and efficiency.

Installed performance seeking control based on supersonic variable inlet/engine coupling model

Abstract With the advancement of the supersonic aero propulsion system, optimizing the combined performance of inlet/engine integration has become increasingly crucial. To solve the coupling inlet/engine problem, a quasi-one-dimensional inlet modeling and drag calculation method are proposed, integrated performance seeking control (PSC) based on the neighborhood-based speciation differential evolution-grey wolf optimizer (NSDE-GWO) is presented and quantitatively analyses the influence of variable geometry inlet regulation on performance. The results reveal that the optimization effect of the ramp angle adjustment is generally better than that of the bleed adjustment, and the NSDE-GWO hybrid algorithm achieves remarkable optimization solutions in all three different modes. The PSC with variable geometry inlet adjustment provides more additional potential for optimization compared with fixed geometry inlet, and the performance can be maximized by adjusting both the bleed adjustment and the ramp angle. This study maximizes the exploitation of potential and has theoretical guidance and practical engineering significance.

Multi-objective aerodynamic optimization of an axisymmetric variable-geometry inlet with a Mach 5 design point

The inlet is a critical component of the air-breathing system of an aircraft engine and an appropriate inlet design can address the issue of aerodynamic contradiction between low and high Mach numbers, restricting aircraft flight over a wide speed range. Therefore, in this study, an axisymmetric variable-geometry inlet with a Mach 5 design point was designed. A multi-point multi-objective optimization design, based on the Kriging surrogate model and non-dominated sorting genetic algorithm-II algorithm, was performed. Wind tunnel tests and numerical simulations were conducted to investigate the inlet performance and flow field details. The steady-state pressure distribution was recorded, and shadowgraph images were obtained simultaneously to comprehensively evaluate the inlet performance. The experimental and numerical results indicate that the design and optimization methods of the inlet are effective. The inlet operated appropriately and stably over a wide range of speeds, and the total pressure recovery (TPR) coefficient reaches 0.421 at the design point. The optimization results show that a 21.36% gain in the TPR coefficient at Ma = 3.0 was achieved at the cost of a 2.44% loss of total pressure recovery at Ma = 5.0. It is also beneficial in terms of the total pressure distortion at Ma = 5.0, which is reduced by 6.54%. This indicates that the inlet design and optimization framework developed in this study is promising for wide use in practical engineering applications.

Model smanjene porudžbine za elektro-hidraulični ventil kontrolera gasnoturbinskog motora

Gas turbine engines (GTE) are widely used in military and industrial applications. Accurate modeling is mandatory to advance GTE control. The present article investigates, experimentally and theoretically, a detailed dynamic model of an electro-hydraulic system that controls a variable geometry inlet guide vanes (VIGV) of turboshaft GTE. A parametric study for the computationally expensive and time-consuming model has been conducted considering the forces affecting the valve's spool and its relatively short settling time. A reduced mathematical model has been developed. The prediction results of the reduced and full-detailed models have been compared with the experimental results. The reduced model has decreased calculation time by 45% to 50 % while keeping the RMSE of the model within 1-2 % away from the actual system's experimental results for the complete operating range. An improvement allows future studies to integrate the whole subsystems of the GTE in a single computationally affordable model.

DES analysis on effects of variable geometry inlet orifice on a centrifugal compressor

A variable geometry inlet configuration can improve the off-design aerodynamic performance of a turbocharger compressor by actively modulating the internal flow field. As the core part of the configuration, the variable geometry orifice is arranged in front of the compressor inducer. Its novelty is to actively regulate the compressor inlet flow area at an off-design point without causing significant impact at the design point. In this paper, the effects of the orifice on compressor performance and internal flow field are investigated using experiments and numerical simulations. The experimental and the numerical results confirm the variable inlet configuration to be a promising method for extending the compressor operation range. The DES calculations reveal incidence angle reduction at inducer inlet, shock wave migration to a lower radius from blade tip, formation of the aft-loaded impeller, reduced difference between jet and wake flows at impeller exit, and turbulent flow enhancement in the diffuser. Based on understanding the orifice’s effects on the centrifugal compressor, a design suggestion is proposed for the variable geometry compressor of this sort.

A composite controller design using an adaptive internal type-2 fuzzy logic system and the fixed-time disturbance observer for an air-breathing hypersonic vehicle with a variable geometry inlet

In this paper, a novel composite controller design technique is addressed for using an adaptive interval type-2 fuzzy logic system (FLS) with the fixed-time disturbance observer (FTDO) such that the enhanced tracking performance is achieved for an air-breathing hypersonic vehicle with a variable geometry inlet (AHV-VGI). First, introducing the variable geometry inlet to take proper mass flow into the engine without any flow spillage ensures enough thrust for acceleration and maneuvering flight. The interval type-2 FLS integrated with an adaptive control algorithm is derived to approximate the complicated nonlinear items in the control strategy online, which assures that the tracking error are semi-globally uniformly bounded. After that, the fixed-time disturbance observer that is constructed to provide the estimations of uncertainty including external disturbance leads to a more practical and robust flight control system for AHV-VGI. The uniform stability of the whole system is proved under the framework of Lyapunov theory. Finally, simulation results and analysis are presented to demonstrate the effectiveness of the proposed composite control scheme.

Compound control of an uncertain hypersonic vehicle model

The extremely broad flight envelope brings remarkable uncertainties to hypersonic vehicles. This paper investigates the longitudinal control problem of hypersonic vehicles with synthetical considerations on multiple modelling uncertainties, especially on time-varying aerodynamic coefficients. To overcome the efficiency loss of aerodynamic control surfaces (ACS), the reaction control system (RCS) is employed to assist the attitude control. An adaptive ACS-RCS compound control is proposed, which deals with uncertain RCS parameters, simultaneously. Other factors including scramjet input saturation, variable geometry inlet, external disturbances and structural flexibilities are also taken into account. Analysis and simulation indicate that preset references can be well tracked with prescribed performances.

Design and analysis of a supersonic axisymmetric inlet based on controllable bleed slots

Aiming at the problem of starting and inlet-engine matching of axisymmetric variable geometry inlet with complex structure, a novel design concept of axisymmetric inlet is proposed based on controllable bleed slots switch. The laws of the typical geometric parameters of multi-slots effecting on inlet start, supercritical and subcritical performances are numerically studied. Accordingly, a three-dimensional aerodynamic design scheme of the inlet operating at Ma1.5-4 and control laws of the bleed slots are gained, which is slightly altered inlet surface and structure is simplified. The aims of minimum starting Mach number to 2 and inlet-engine matching inlet are achieved by controlling switch of bleeding slots, and inlet operates well at high total pressure recovery and low exit Mach number. The results show that: at Ma=2, the inlet starts with 30% bleeding and 16.5% total pressure recovery coefficient improving; At Ma=3, mass flow of inlet-engine matches with 23% subsonic bleeding but cost of total pressure loss about 2.6%.

Design and validation of a two-dimensional variable geometry inlet

Abstract The design of a two-dimensional variable geometry inlet which applied to a tandem type turbine-based combined cycle (TBCC) propulsion system was investigated in the present paper through three-dimensional simulations and wind tunnel tests. The operation Mach number range was between 0 and 3. A multi-ramp geometry scheme was adopted to achieve acceptable performance at different inflow Mach number. The first ramp angle was fixed whilst the angles of the second and the third ramps were variable at different inflow Mach numbers. The Mach numbers at throat region were maintained between 1.3 and 1.5 at different inflow Mach numbers according to this variable geometry scheme. A fixed geometry rectangular-to-circular shape diffuser was adopted to improve aerodynamic performance of the inlet. Three-dimensional numerical simulations were carried out between Ma1.5 and Ma3.0. The results indicated that good aerodynamic performance can be achieved at different inflow speed. At the design point, total pressure recovery of the inlet was 0.66 at critical condition. Wind tunnel validation experiment tests were conducted at Ma2.0, showing the movement of terminal shock wave from downstream to upstream as the back pressure increased. The inlet operated at supercritical, critical and subsonic conditions at different back pressure.

Transient Behavior in Variable Geometry Industrial Gas Turbines: A Comprehensive Overview of Pertinent Modeling Techniques.

Generally, industrial gas turbines (IGT) face transient behavior during start-up, load change, shutdown and variations in ambient conditions. These transient conditions shift engine thermal equilibrium from one steady state to another steady state. In turn, various aero-thermal and mechanical stresses are developed that are adverse for engine’s reliability, availability, and overall health. The transient behavior needs to be accurately predicted since it is highly related to low cycle fatigue and early failures, especially in the hot regions of the gas turbine. In the present paper, several critical aspects related to transient behavior and its modeling are reviewed and studied from the point of view of identifying potential research gaps within the context of fault detection and diagnostics (FDD) under dynamic conditions. Among the considered topics are, (i) general transient regimes and pertinent model formulation techniques, (ii) control mechanism for part-load operation, (iii) developing a database of variable geometry inlet guide vanes (VIGVs) and variable bleed valves (VBVs) schedules along with selection framework, and (iv) data compilation of shaft’s polar moment of inertia for different types of engine’s configurations. This comprehensive literature document, considering all the aspects of transient behavior and its associated modeling techniques will serve as an anchor point for the future researchers, gas turbine operators and design engineers for effective prognostics, FDD and predictive condition monitoring for variable geometry IGT.

Numerical and experimental investigation of turbocharger compressor low-end performance improvement using a variable geometry inlet orifice

Variable geometry orifice located upstream of a centrifugal impeller has been proposed to improve compressor low-end performance, by reducing compressor inlet flow area. The inlet flow area reduction is achieved by actuating the orifice flow area. The effects of the flow area reduction on compressor performance and the physical mechanisms controlling performance were investigated in the current work using numerical simulations and physical experiments. At the investigated compressor speed, with reduced inlet flow area, compressor efficiency at high flow rates is decreased by 2.01 percentage points based on the numerical predictions and by 6.47 percentage points based on the physical data. At low flow rate, however, compressor efficiency can be improved by 2.26 percentage points based on the numerical predictions and by 2.88 percentage points based on the physical data. Besides the efficiency, the inlet flow area reduction shifts the compressor stability limit toward the lower flow rate by 9.09% based on the numerical results and 41.13% based on the physical experiment and improves the compressor peak pressure ratio by 0.55% based on both the numerical and experimental data. At the flow rates lower than the peak efficiency point, it is beneficial to actuate the orifice to improve the compressor low-end performance. At flow rates higher than the peak efficiency point, it is necessary to deactivate the orifice to avoid the inlet flow area reduction that induces flow loss and degrades compressor performance.

Scramjet Operation Guaranteed Longitudinal Control of Air-Breathing Hypersonic Vehicles

Due to the unique airframe/scramjet integration of air-breathing hypersonic vehicles (AHVs), flight status has complex influences on scramjet efficiency. This article studies the longitudinal control problem of AHVs configured with the variable geometry inlet, in parallel with full considerations on scramjet operation. In velocity loop, an adaptive velocity reference generator is constructed to accommodate the state-dependent constraint on fuel-to-air equivalency ratio that is required by the avoidance of scramjet thermal choking. Meanwhile in altitude loop, the state-dependent constraint on angle-of-attack is handled by robust adaptive control laws, in which case the inlet inhales enough airflow. The developed controller is able to maintain necessary conditions for scramjet operation while accommodating practical uncertain factors and ensuring satisfactory tracking performances.

Barrier Lyapunov function based reinforcement learning control for air-breathing hypersonic vehicle with variable geometry inlet

Based on barrier Lyapunov functions, a reinforcement learning control method is proposed for air-breathing hypersonic vehicles with variable geometry inlet (AHV-VGI) subject to external disturbances and diversified uncertainties. The longitudinal dynamic for the AHV-VGI is transformed into strict feedback form. Controllers for velocity and altitude subsystems are designed, respectively. Taking advantage of the reinforcement learning strategy, two radial basis function (RBF) neural networks are applied to estimate the “total disturbances” in the flight control system. Actor network is used for generating the estimate of the disturbance. Critic network is used for evaluating the estimation accuracy. Prescribed tracking performances and state constraints can be guaranteed by introducing barrier Lyapunov functions (BLFs). Tracking differentiators are used to generate the derivatives of virtual controllers in the backstepping design process. Simulation results illustrate the effectiveness and advantages of the proposed control strategy.

ESO-based fault-tolerant anti-disturbance control for air-breathing hypersonic vehicles with variable geometry inlet

The fault-tolerant anti-disturbance control problem for air-breathing hypersonic vehicles with variable geometry inlet (AHV-VGI) is investigated. The VGI technique enlarges the AHV flight envelope at the expense of the system to inevitably possess unknown disturbances, model uncertainties and actuator faults. A novel fault-tolerant control strategy is proposed under the back-stepping control scheme based on extended state observer (ESO) and dynamic inversion. In each step, two ESOs are designed. The first one estimates the virtual control signals, and the second one approximates the total uncertainties. Dynamic inversion is introduced into the controller to deal with the non-affine actuator faults. In particular, the ESOs are activated successively in the designed controller. ESO estimation errors and output tracking errors of the AHV-VGI system are proved to be arbitrarily small in theory. Simulation results are provided to demonstrate the effectiveness and superiority of the proposed control strategy.

Hypersonic flight control considering parametric variations and VGI effects

Despite advantages of variable geometry inlet (VGI) in improving scramjet efficiency, a concern of its negative effects on aerodynamics persists. This paper presents a novel longitudinal control for the hypersonic vehicle model with further considerations on both strong VGI effects and unpredictable parametric variations, which is practical but hard to handle. Our design uses an auxiliary signal and a bound adaptation mechanism to synthetically accommodate VGI effects (including VGI servomechanism characteristics and VGI couplings with aerodynamics), time-varying parameters and structural flexibility while achieving good tracking performances via a relatively low-dimension adaptive algorithm.

Adaptive Control of Variable Geometry Inlet–Configured Air-Breathing Hypersonic Vehicles

This paper studies the longitudinal fault-tolerant control problem for a class of variable geometry inlet–configured air-breathing hypersonic vehicles, whose inlet length varies dynamically to ensure an efficient scramjet thrust. After lumping the effects of uncertain parameters, external disturbances, flexible dynamics, actuator faults, and variable inlet into the linearly parameterized form, a parameterized control-oriented model (PCOM) is derived for design purpose. To handle the time-varying uncertain parameter vectors involved in the PCOM, a novel bound estimation method is developed, while greatly reducing the required parameter update laws. In the adaptive back-stepping design for altitude subsystem, the command filter technique is implemented to circumvent the analytical derivative calculations of virtual controls that are unmanageable by a standard back-stepping procedure because of the time-varying uncertain factors in the PCOM. The corresponding tracking errors are regulated into adjustable residual sets. A simulation study is implemented to verify the developed controller.

Sliding Mode Differentiator Based Tracking Control of Uncertain Nonlinear Systems with Application to Hypersonic Flight

AbstractThis paper presents a performance‐guaranteed adaptive back‐stepping design for a class of nonlinear systems with uncertainties and disturbances. To circumvent the increasing complexity caused by the repeated analytic differentiations in back‐stepping, sliding mode differentiation technique is employed to estimate the derivative of the virtual control. Compared with the well‐known command filtered back‐stepping, no compensating signal is required. Besides, time‐varying parameters, system uncertainties and external disturbances are compensated using nonlinear damping technique, while the output tracking error is regulated in the prescribed range with the adjustable convergence speed and steady‐state error. As a verification example, this method is applied to the longitudinal control of an air‐breathing hypersonic vehicle configured with the variable geometry inlet.

Buzz evolution process investigation of a two-ramp inlet with translating cowl

In order to satisfy the requirement of high integration, the inlet equipped with translating cowl, which is able to adjust the geometries of combustor and inlet simultaneously, is proposed and studied. Numerical investigations are conducted to obtain hysteresis loop, stability boundary and buzz evolution process with various internal contraction ratios in wide range of flight Mach numbers. The dynamic mesh method is utilized to simulate the geometric adjustment. The results reveal that the buzz evolution process has obvious hysteretic characteristics under the change of translating direction. Meanwhile, the mechanism of inlet buzz mode transition is provided. Then, the effects that the translating velocities have on the oscillatory frequency, position of separation leading edge and dynamic drag are given. The higher velocity is able to restrain the intension of separation oscillation and enlarge the stable region, but has insignificant effect on the reduction of oscillatory frequency and dynamic drag. For specific velocities, there is no oscillation. Therefore, the appropriate velocity can be selected for the improvement of inlet stability. This research gives a full insight into the dynamic performance of a hypersonic variable-geometry inlet.