Scramjet (supersonic combustion ramjet) engines are often seen as a promising alternative to place payloads in the Earth's orbit. Such air-breathing engines have a simple structure and few moving parts. On the other hand, high heat fluxes and pressure loads on the walls, shock-wave-boundary-layer interactions, and the risk of choked flow inside the isolator channel are a few examples of obstacles that need to be addressed during scramjet design. Therefore, this study aims to evaluate of different air freestream conditions on the flow field in a scramjet inlet (compression ramps and isolator) through detailed three-dimensional computational fluid dynamics (CFD) simulations. The Mach number, flight altitude, and angle of attack were the evaluated conditions. Moreover, this study also focuses on the behavior of the boundary layer separation located at the compression ramp corners, isolator entrance, and scramjet sidewalls. Regarding the Mach number variation, the results showed that high Mach numbers yielded high-pressure levels throughout the engine. Furthermore, a higher altitude promoted a lower total pressure field. Considering the angle of attack changes, it is evident that a higher angle of attack results in a decrease in airflow pressure, while an increase in the total pressure along the walls is observed. By investigating these freestream parameters, this work can contribute to the early phase of engine design, avoiding critical failures in the scramjet structure due to aerodynamic load and thermal stress.

Three-Dimensional CFD Investigation of a Scramjet Inlet under Different Freestream Conditions

Flow-induced vibration (FIV) on two tandem cylinders with forced convection is investigated numerically at a constant Re=150. Elastically mounted cylinder with four different values of corner radii ( r*=r/R:r=radius of fillet ;R=Radius of circle) =0 (square cylinder), 0.25, 0.75 and 1.0 (circular cylinder) with two spacing ratio ( L/D)=4 and 2 are studied. Transverse oscillations are generated from the cylinder having non-dimensional mass ( m*)=10. The structural damping coefficient is assigned a zero value with varying reduced velocity. Both cylinder's surfaces are maintained at a higher constant temperature of T*=1, and incoming flow is set to be at T*=0 with Prandtl Number (Pr)=0.7. The effect of r* and L/D is observed on the flow structure and FIV parameters. Flow characteristics at such as steady flow, reattachment and unsteady flow are examined. A "shift" in vibrational amplitude is noted from r*= 1 and 0.75 to r*=0 and 0.5, respectively. The downstream cylinder ( Dc) experiences a hike in vibration amplitude due impingement of vortex shedding from the upstream cylinder (U c). r*=1 has 18.1% higher vibrational amplitude than r*=0 at their respective lock-in regimes for Dc. For L/D=2, vortices from upstream and downstream cylinders interact to form C(2S) and 2S types of vortex shedding. Different regimes such as single body, reattachment, and co-shedding have been observed while changing L/D . r*=0.75 results in 13.3% higher oscillation amplitude as compared to r*=0.5 for Dc. Average Nusselt number strongly depends on flow topology, corner radius, and vibrational amplitude.

Effect of corner radius on flow topology and heat transfer from free oscillating tandem cylinders at low Reynold Number

Scramjet (supersonic combustion ramjet) engines are often seen as a promising alternative to place payloads in the Earth's orbit. Such air-breathing engines have a simple structure and few moving parts. On the other hand, high heat fluxes and pressure loads on the walls, shock-wave-boundary-layer interactions, and the risk of choked flow inside the isolator channel are a few examples of obstacles that need to be addressed during scramjet design. Therefore, this study aims to evaluate of different air freestream conditions on the flow field in a scramjet inlet (compression ramps and isolator) through detailed three-dimensional computational fluid dynamics (CFD) simulations. The Mach number, flight altitude, and angle of attack were the evaluated conditions. Moreover, this study also focuses on the behavior of the boundary layer separation located at the compression ramp corners, isolator entrance, and scramjet sidewalls. Regarding the Mach number variation, the results showed that high Mach numbers yielded high-pressure levels throughout the engine. Furthermore, a higher altitude promoted a lower total pressure field. Considering the angle of attack changes, it is evident that a higher angle of attack results in a decrease in airflow pressure, while an increase in the total pressure along the walls is observed. By investigating these freestream parameters, this work can contribute to the early phase of engine design, avoiding critical failures in the scramjet structure due to aerodynamic load and thermal stress. 

Three-dimensional CFD investigation of a scramjet inlet under different freestream conditions

Controller design for a realistic scramjet (Supersonic Combustion Ramjet) model is an extremely computationally intense process. To mimic the real-time scramjet performance, several researchers have developed linear models, nonlinear models, computational fluid dynamic (CFD) based models, etc. The linear models or nonlinear models based on ordinary differential equations are not sufficient to capture the complete dynamics of the scramjet; whereas CFD based models are highly computationally intense - which may vary from hours to days to complete one full closed-loop simulation of a realistic test case. The scramjet engine model can be divided in to three parts; inlet, combustor and exhaust. In this paper, the key focus is to develop the inlet model from the CFD simulations for various test cases and then capture vital scramjet engine parameters, which are later required for controller design for the scramjet engine. The models developed from the captured vital scramjet parameters has two advantages; high fidelity model and are less computationally intensive. The simulations are performed for various test cases at operating Mach numbers of 7, 6.5 and 6, angle of attack of 0 deg, ±1 deg, and ±2 deg, and various cowl angles. Control oriented polynomial inlet models are developed from the CFD data for all the operating points, the accuracy of the developed polynomial models is observed in terms of low residual errors. 

Development of a Control Oriented Scramjet Engine Inlet Model

Effect of ramp leading-edge blunt on the performance of a Mach4 scramjet intakes

Numerical Simulation of Flow through Scramjet Inlet - Isolator Model with Pressure Feedback

This numerical study investigated the flow-induced vibration (FIV) on non-heated and heated cylinders with different normalized corner radii (r*) at different Reynolds numbers (Re). Four different values of r* were considered (i.e., 0 (square cylinder), 0.5, 0.75, and 1.0 (circular cylinder)) at three different Re: 100, 150, and 200 within the laminar regime. The cylinder constrained in the axial direction and oscillated transversally was considered for a fixed nondimensional cylinder mass (m*)  of 10 and a reduced velocity (Ur) of 4.92. The effect of r* and Re could be seen in the vibration modes of cylinders. The two-dimensional incompressible Navier–Stokes and energy equations were solved together with Newton’s Second Law governing the motion of the cylinder with the help of a computational solver. Four different modes were observed in this study: Mode-I characterized by exceptionally low amplitude; Mode-II characterized by fluctuating amplitude known as hysteresis (beating); Mode-III characterized by high amplitude due to synchronization or lock-in; and Mode-IV characterized by the monotonic oscillation of fixed amplitude. For r* = 1, synchronization phenomenon/lock-in was observed. For the heated cylinder cases, due to the change in the normalized corner radius, a notable change in nondimensional vibrational amplitude A/D and the average Nusselt number Nuavg was seen. It was observed that A/D was higher when lock-in occurred (at Re = 100 and r* = 1), leading to a rise in Nuavg by 47.9% compared to Re = 100 and r* = 0. Due to the change in r*, a shifting phenomenon was observed at Re = 150, r* = 0.75 and Re = 200, r* = 1. A major change in Nuavg was observed from the circular cylinder to square cylinder at different Re. The beating phenomenon was observed at Re = 100 for r* = 0.75, which was similar to that occurring at Re = 150 and r* = 0.5, and those at Re = 200 and r* = 0. Heat transfer and wake structure parameters were found to be dependent on r* and Re.

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Flow around an Oscillating Cylinder at Low Reynolds Number with Forced Convection: Effect of Corner Radius and Reynolds Number


 Flow-induced vibration (FIV) of the modified single-cylinder with a change in corner radius has been investigated in a laminar flow regime with Re = 100 and Pr = 0.7. The corner radius (r: corner radius, :R cylinder characteristic length) is changed from 1 to 0 and two angles α; 0° and 45° are used. The Cylinder is elastically supported with heating at a constant temperature at the boundaries. Vibrations are restricted to the transverse direction. Computation is carried out with a fixed mass ratio m* = 10 and varying reduced velocity Ur = 2 ∼ 8. The two-dimensional incompressible Navier-Stokes equations and energy equations are coupled together. Navier stokes equation used with FIV equation of elastically supported cylinder to have flow solutions. Lock-in synchronization can be observed at Ur = 5 and Re = 100 at r* = 1 which leads to severe vibration and maximum vibrational amplitude A/D while amplitude modulation has been observed at Ur = 5 for the square cylinder. Based on the mode of vibration whole study has been divided into 4 ranges of vibration. Mode-I, where the amplitude is very low; Mode-II, fluctuating amplitude known as hysteresis (Beating); Mode-III; amplitude is at the maximum because of lock-in synchronization; Mode-IV, normal vibrational amplitude. Different modes are compared with the change in Ur, r* and α. The effect of Ur is visible on the Nusselt number as more vibration leads to a high value of averaged Nusselt number NuAvg. Vortex shedding is changed from C(2S) to 2S as the corner radius is modified. Results give a deep insight into heat transfer getting changed by changing three different parameters and will make a base for future study of tube bundles in heat exchangers with FIV.

Analysis of Corner Radius on the Free Oscillating Cylinder With Heat Transfer and Flow Pattern at Low Reynolds Number


 Flow-induced vibration (FIV) of the modified tandem-cylinder with a change in corner radii has been investigated in a laminar flow regime with Re = 150 and Pr = 0.7. The corner radius (r: corner radii, R: cylinder characteristic length) r* = 0, 0.5, 0.75 and 1 are used at a constant angle of attack of 45°. The cylinders are allowed to vibrate in transverse direction while restricted in axial direction with spacing ratio L/D = 4. Computation is carried out with a fixed mass ratio m* = 10 and varying reduced velocity Ur = 2 ∼ 10. Constant heating is provided by keeping boundary at a constant temperature. The two-dimensional incompressible Navier-Stokes equations and energy equation are coupled together. Navier-Stokes equations are used with FIV equation of elastically supported cylinder to have flow solutions. Lock-in phenomenon for most of the configuration is occurring at Ur = 6 where vibrational amplitude for most of the configuration is peaked. At Ur = 6 for square cylinder, pseudo ‘2P’ can be observed in the wake of r* = 0. Vortices at Ur = 6 are not merged properly to form a definite type of vortex shedding, although in further downstream weak 2S vortex shedding can be observed. Heating of cylinder is affected by various parameters such as corner radii and spacing ratio with other factors such as early flow separation, reattachment, and vibrational amplitude. Maximum values of Average Nusselt number Nuavg is at Ur = 6 for circular cylinder, whereas minimum lies at Ur = 2 for square downstream cylinder. Results give a deep insight into heat transfer getting changed by changing different parameters and will make a base for future study of tube bundles in heat exchangers with FIV.

Yuvraj Sarout

Papers

Numerical Simulation of Flow through Scramjet Inlet - Isolator Model with Pressure Feedback

Flow around an Oscillating Cylinder at Low Reynolds Number with Forced Convection: Effect of Corner Radius and Reynolds Number

Analysis of Corner Radius on the Free Oscillating Cylinder With Heat Transfer and Flow Pattern at Low Reynolds Number

Effects of Corner Radii on Vortex-Induced Vibration With Forced Convection Heat Transfer From Angled Tandem-Cylinder at Low Re

Effect of corner radius on flow topology and heat transfer from free oscillating tandem cylinders at low Reynold Number