Turbine-based Combined Cycle Inlet Research Articles

Multi-fidelity simulation of inlet mode transition with smooth thrust of turbine based combined cycle

A multi-fidelity simulation method of external and internal flow has been developed using commercial software to achieve a smooth thrust of the turbine-based combined-cycle (TBCC) propulsion system. This platform enables the investigation of the flow field and performance of the TBCC propulsion system at different mode transition schemes. The integrated multi-fidelity simulation includes the inlet, turbojet engine, ramjet engine, and nozzle, providing insights into the operation process of the TBCC propulsion system during the transition from turbojet mode to ramjet mode. Three mode transition schemes are proposed: critical mode transition, constant aerodynamic interface plane (AIP) Mach number mode transition, and linear mode transition. From the perspective of TBCC inlet, the performance of the critical mode transition exhibits the best performance among these mode transition schemes, while the linear mode transition performs the worst. However, from the viewpoint of the TBCC propulsion system and the hypersonic vehicle, the performance of constant AIP Mach number mode transition is the best. The non-dimensional thrust increases almost linear from 1.0 to 1.2, enabling hypersonic vehicle to accelerate steadily during the transition from turbojet mode to ramjet mode.

Analysis of the impact of key similarity criteria numbers of TBCC inlet during the mode transition

Abstract A simplified configuration was developed to facilitate the mode transition process within an over-under Turbine-Based Combined Cycle (TBCC) inlet. Leveraging dynamic mesh technology, an unsteady numerical simulation of the mode transition was conducted, emphasising the flow characteristics of the mode transition and the impact of key similarity criteria numbers. The findings indicate that at an incoming Mach number of 2.0, the mode transition is paired with a continuous alteration in the capture mass flow of the high-speed duct. This continual change instigates the inlet unstarting, with subsequent flow characteristics being contingent on the historical effect, exhibiting a degree of hysteresis characteristics. When the scale effect is considered, it is observed that a larger model scale results in higher Reynolds (Re) and Strouhal (St) numbers. This directly contributes to a notable delay in the unstart moment, a decrease in the unstart interval, and an enlargement of the hysteresis loop. An examination of control variables reveals that the Re number marginally influences mode transition characteristics, while the St number’s effect constitutes approximately 90% of the scale effect. This conclusively demonstrates that the St number is the predominant similarity criterion number in the mode transition process.

Investigation of the impact of splitter rotation speed on mode transition characteristics of an over-under turbine-based combined cycle inlet

Investigation of the impact of splitter rotation speed on mode transition characteristics of an over-under turbine-based combined cycle inlet

Unsteady flow characteristics in an over-under TBCC inlet during mode transition under unthrottled and throttled conditions

The study presents an experimental exploration into the mode transition of an over-under TBCC (Turbine-Based Combined Cycle) inlet, with a specific emphasis on the flow characteristics at off-design transition Mach number. A systematic investigation was undertaken into the mode transition characteristics in both unthrottled and throttled conditions within a high-speed duct, employing high speed Schlieren and dynamic pressure acquisition systems. The results show that the high-speed duct faced flow oscillations primarily dictated by the separation bubble near the duct entrance during the downward rotation of splitter, leading to the duct’s unstart under the unthrottled condition. During the splitter’s reverse rotation, a notable hysteresis of unstart/restart of the high-speed duct was observed. Conversely, hysteresis vanishes when the initial flowfield nears the critical state owing to downstream throttling. Moreover, the oscillatory diversity, a distinctive characteristic of the high-speed duct, was firstly observed during the mode transition induced by throttling. The flow evolution was divided into four stages: an initial instability stage characterized by low-frequency oscillations below 255 Hz induced by shock train self-excitation oscillation and high-frequency oscillations around 1367 Hz caused by the movement of separation bubble. This stage is succeeded by the “big buzz” phase, comprised of pressure accumulation/release within the overflow-free duct and shock motion outside the duct to retain dynamic flow balance. The dominant frequency escalated with the increase of the internal contraction ratio in the range of 280 Hz to 400 Hz. This was followed by a high-frequency oscillation stage around 453 Hz dominated by a large internal contraction ratio with low pulsating energy, accompanied by a continuous supersonic overflow. Lastly, as the splitter gradually intersected the boundary layer of the first-stage compression surface, the capture area and the turbulence intensity of the incoming flow underwent a sudden shift, leading to a more diverse flow oscillation within the duct, manifested as various forms of mixed buzz.

Conceptual design methodology and performance evaluation of turbine-based combined cycle inward-turning inlet with twin-design points

Turbine-based combined cycle (TBCC) engines attract intensive attention due to adequate high working efficiency within the full speed range of air-breathing vehicles. Challenges of TBCC engines lie mostly in common-used components in particular the inlet system, which needs to satisfy the mass flow distribution of different sub-engines and to reconcile the performance requirement in the full speed range. In the present work, a new conceptual design methodology of the three-dimensional inward-turning TBCC inlet with twin-design points is proposed according to the basic flow field with double incident shock waves. The shock structures and flow field parameters at the high-speed design point Ma=4 and mass flow distribution at the low-speed design point Ma=3 both can be designed by the basic flow field. On that basis, a typical inlet model is designed and the corresponding aerodynamic performance is evaluated at two design points. Simulation results prove that the shock structure, the mass flow distribution, and the averaged throat parameters of the TBCC inlet are all consistent with the basic flow field with sufficient accuracy at twin-design points, where the maximum relative error is only 6.3%. Meanwhile, the aerodynamic performance of the inlet shows that the inlet has stable and efficient operation characteristics, which fully affirms the feasibility of the design method.

Studies on unsteady mode transition of a turbine based combined cycle (TBCC) inlet with multiple movable panels

Using the overset grid method, this paper numerically studies the unsteady mode transition from the turbojet mode to the ramjet mode of a 2D TBCC inlet with multiple movable panels, for the first time. The flow field during mode transition is highly unsteady so that the steady simulation is not appropriate. Under the baseline mode transition strategy, the instability of shock waves near the throat causes the oscillation of inlet exit performance parameters. In addition, mode transitions under different turbojet back pressure are investigated, and the oscillation occurs in most cases. In order to suppress the oscillation and increase the total pressure recovery, the Unsteady Panel to Panel Optimization Method (UPPOM) is proposed to optimize the final rotation angles of movable panels. In UPPOM, the movable panels operate in a designed motion pattern, where the mode transition process is divided into two steps, namely geometry adaption and flowpath switching. After geometry adaption, the oscillation is successfully removed, and the total pressure recovery at the turbojet flowpath exit is increased by 4.24%. In the second step of optimization, a new optimization index of Weighted Total Pressure Recovery (WTPR) is employed to increase the overall performance of TBCC inlet. In the sense of the WTPR, the performance of the optimization result is increased by 5.92%.

The design and validation of over/under turbine-based combined cycle inlet

The design constraints including capture area and mode transition point of turbine-based combined cycle (TBCC) inlet are determined by the performance analysis of combined cycle propulsion system. According to the mass flow and thrust requirement of the combined cycle engine, the capture area of 1.0 m2 and mode transition between Ma 2.2 and 2.5 are recommended. Based on these two quantities an over/under TBCC inlet which can operate from takeoff to Ma 4.0 is designed. The variable geometry scheme of TBCC inlet is shown at different flight Mach number. Three dimensional numerical simulations of full-scale model and wind tunnel test of 8-percent scale model are explored to verify this inlet design method. The results from the numerical simulations and experimental tests indicate that the TBCC inlet could work properly during this Mach number range. The mass flow captured by the inlet and total pressure recovery at turbine/ramjet aerodynamic interface planes (AIP) meet the requirement of the TBCC propulsion system.

Suppression and utilisation of aeroelastic behaviour in turbine-based combined cycle inlet

This study develops a two-way loosely coupled aeroelastic analysis framework based on a finite-volume fluid solver, a nonlinear finite-element solid solver and the Mesh-based parallel Code Coupling Interface. Research focuses on aeroelastic behaviour in a turbine-based combined cycle inlet after verifying the fluid solver and the coupling strategy through three benchmarks consisting of the inlet experimental model, the classical panel flutter problem and the deformation of a cantilever plate subjected to a shock tube flow. Coupling calculation shows that structural damping is limited only to the vibration suppression of deformable components under constant backpressure but exerts no evident influence on flow field oscillation induced by splitter plate vibration or perturbation from downstream dynamic backpressure. Interestingly, panel deformation (or forced vibration) has a positive impact on the stabilisation of the flow field. The use of a flexible panel with low thickness (e05) successfully prevents the shock train from transitioning, stabilising the performance profiles at the outlet even under dynamic backpressure. Pressure adjustment in the potentially unstable region through panel deformation is assumed to be the solution to weakening the disturbance from splitter plate vibration, which differs from the energy transfer theory under dynamic backpressure that is often found in the literature.

Numerical Simulation of Terminal Shock Oscillation in Over/Under Turbine-Based Combined-Cycle Inlet

Abstract The physical characteristics of self-sustain shock oscillation and the key factors that affect the shock oscillation in turbine-based combined-cycle(TBCC) inlet were investigated through unsteady numerical simulation method in this paper. The terminal shock oscillation in the throat was caused by the separation bubble appeared in the lower wall of the turbojet flowpath. The angle of the splitter and the offset of the diffuser were the main factors which affect the characteristics of the shock oscillation. When the angle of the splitter increased from 0 deg to 12 deg, the frequency of terminal shock increased from 100Hz to 133Hz; while when it was greater than 18 deg the terminal shock oscillation phenomenon disappeared. Different offset of the turbojet diffuser affect the motion of terminal shock in the inlet. When the y-coordinate value of the control point (ym) in the turbojet diffuser was smaller than 1.5, the shock oscillated in the inlet; when ym was greater than 2.0, the shock oscillation disappeared. The bleed in the diffuser was able to control the oscillation of the terminal shock.

The flowfield and performance analyses of turbine-based combined cycle inlet mode transition at critical/subcritical conditions

The fluid dynamics and performance analyses of steady and continuous combined cycle inlet mode transition at critical/subcritical conditions were investigated through wind tunnel tests and three dimensional unsteady numerical simulations. When the inlet operated at critical condition, the terminal shock was unsteady and oscillated in the frequency between 40 Hz and 60 Hz around the shoulder of inlet and the downstream of cowl leading edge. In critical inlet mode transition the performance parameters of diffuser exit varied with positions of terminal shock. When the inlet operated at subcritical condition, terminal shock was steady at the upstream of cowl leading edge. The continuous mode transition test results reveal that the shock can be steady at subcritical condition. Considering the shock stability and performance parameters at the diffuser exit, subcritical inlet mode transition is better than critical condition for combined cycle inlet investigated in this paper.

Preliminary research of terminal shock motion in tandem configuration turbine-based combined cycle inlet

ABSTRACTThe pressure oscillation and terminal shock motion in a two dimensional inlet, which was designed for tandem configuration turbine-based combined cycle propulsion systems was investigated experimentally and numerically, respectively. The inlet was characterised by a bleed cavity upstream the inlet throat, an S-shape rectangular-to-circular diffuser and flowpaths for a turbine and a ramjet engine. The terminal shock motion was calculated through a second-order unsteady Reynolds-averaged Navier-Stokes scheme. The pressure and the terminal shock were unsteady when the combined cycle inlet operated at different conditions. With the terminal shock located in the throat and at the shoulder of the third ramp of the TBCC inlet, the pressure oscillation was significant and the shock exhibited unsteady streamwise motion with an oscillatory pattern. The amplitude of shock oscillation at these two conditions was 6mm and 12mm, respectively. When the shock was located downstream of the throat and upstream of the cowl lip, it oscillated in a small range. We defined this motion as the “shake” of the shock. This unsteady behaviour of the shock was caused by flow separation in the combined cycle inlet diffuser.

Unsteady flow characteristic analysis of turbine based combined cycle (TBCC) inlet mode transition

A turbine based combined cycle (TBCC) propulsion system uses a turbine-based engine to accelerate the vehicle from takeoff to the mode transition flight condition, at which point, the propulsion system performs a “mode transition” from the turbine to ramjet engine. Smooth inlet mode transition is accomplished when flow is diverted from one flowpath to the other, without experiencing unstart or buzz. The smooth inlet mode transition is a complex unsteady process and it is one of the enabling technologies for combined cycle engine to become a functional reality. In order to unveil the unsteady process of inlet mode transition, the research of over/under TBCC inlet mode transition was conducted through a numerical simulation. It shows that during the mode transition the terminal shock oscillates in the inlet. During the process of inlet mode transition mass flow rate and Mach number of turbojet flowpath reduce with oscillation. While in ramjet flowpath the flow field is non-uniform at the beginning of inlet mode transition. The speed of mode transition and the operation states of the turbojet and ramjet engines will affect the motion of terminal shock. The result obtained in present paper can help us realize the unsteady flow characteristic during the mode transition and provide some suggestions for TBCC inlet mode transition based on the smooth transition of thrust.

Aerodynamic Design and Numerical Simulation of Over-under Turbine-based Combined-cycle (TBCC) Inlet Mode Transition

A parameterized design method is established for mode transition of over-under TBCC inlet and the design variables are optimized by Multi-Island Gene Algorithm using auto-CFD solution. Dynamic overset grid technology is utilized tocontrol and simulate the coupled rotation of both the flow splitter and ramjet cowl of TBCC inlet. Mach number effects, time effects and rotating patterns of the splitter during TBCC mode transitionare studied systematically by unsteady simulation in contrast to quasi-steady numerical result,and which shows that all these factors have great influence on the dual-flowpathinlet throat performance as well as the aerodynamic characteristics with similar hysteresis effects.