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A modification in the ramjet engine, known as the Supersonic Ramjet Combustion, completes the combustion at supersonic speeds. Inside the combustion chamber, the mixing of fuels and the entire combustion procedure completes in milliseconds. So, the combustion chamber's flow physics is highly complicated. Through this study, the target is to improve the combustion efficiency inside the combustion chamber, thereby improving the performance of the scramjet engine. For this study, the performance of a strut-based flame stabilizer was analyzed in various positions, and the impact on energy efficiency and combustion performance is evaluated. SST k-ω model of turbulence is used to work out the Navier-stokes equation. To validate data from the experiment, a single strut configuration was considered for the next step, i.e., the comparison of the available data with a three-strut configuration. While considering the three-strut layout, in the x and y directions, secondary struts are placed, while the position of the primary strut remains constant. Only the flow from the primary strut is considered for the analysis of combustion performance out of three struts. From the obtained results, it is clear that the significant factor in improving energy efficiency is positioning the secondary strut in the present three-strut layout. The experiment results state that the combustion efficiency is boosted by 33.86% compared to a single strut combustor. It was also found that there was a considerable decrease in the level of unburned fuel, which makes the configuration more economical. The placement of struts plays a vital role, as any fault in the configuration makes it less efficient than a single strut layout. Other elements that boost combustion efficiency are expansion fans and shock reflection inside the primary zone of combustion and the secondary strut region. With the inclusion of secondary struts, the static wall pressure also escalated. A discrete flow was also observed on the combustion walls for some particular strut layouts. An increase in combustion efficiency was seen when both primary and secondary struts were placed near each other and also for reacting flow from the primary strut alone. There arises no need to supply fuel to secondary struts. So, overall fuel efficiency is improved, making the whole system energy-efficient. • Primary strut is considered for the analysis of combustion performance out of three struts. • The significant factor in improving energy efficiency is positioning the secondary strut in the present three-strut layout. • The combustion efficiency is boosted by 33.86% compared to a single strut combustor. • The intensity of combustion also increased which is evident from static temperature plots. • Shear shock layer enhances the mixing rate by intensifying turbulence phenomena. [ABSTRACT FROM AUTHOR]

In the paper (Theoret Comput Fluid Dyn 36:705–722, 2022), we analyzed acoustic receptivity of the boundary layer on a flat plate in Mach 6 flow at various angles of attack (AoA). It was shown that slow and fast acoustic waves passing through: a bow shock at AoA = - 5 ∘ , a weak shock induced by the viscous–inviscid interaction at AoA = 0 ∘ , or an expansion fan at AoA = 5 ∘ , excite dominant modes F and S in a small vicinity of the plate leading edge. The present paper extends this analysis to the cases of receptivity to entropy and vorticity waves. Similar to the case of acoustic receptivity, modes F and S of about equal amplitude are excited in a small vicinity of the plate leading edge. These modes propagate downstream in accord with the two-mode approximation model accounting for the mean-flow nonparallel effects and the intermodal exchange mechanism. Cross-comparisons of the initial amplitudes of excited modes help to evaluate the relative role of acoustic, entropy and vorticity waves in the second-mode dominated transition. [ABSTRACT FROM AUTHOR]

The results of calculations of the convective heating of a sharp plate placed in a supersonic flow at a speed of M = 6–8 are presented. The NERAT-2D code is used for calculations, which implements the Reynolds-averaged Navier−Stokes equations, together with Baldwin–Lomax and Prandtl algebraic models of turbulence. Good agreement is shown with the experimental data for convective heating in a turbulent boundary layer. The distribution of gas-dynamic functions is analyzed in different cross sections of the plate within the flow. [ABSTRACT FROM AUTHOR]

Direct numerical simulation and theoretical analysis of acoustic receptivity are performed for the boundary layer on a flat plate in Mach 6 flow at various angles of attack (AoA). Slow or fast acoustic wave passes through: a bow shock at AoA = - 5 ∘ , a weak shock induced by the viscous–inviscid interaction at AoA = 0 ∘ or an expansion fan emanating from the plate leading edge at AoA = 5 ∘ . The study is focused on cases where the integral amplification of unstable mode S (or Mack second mode) is sufficiently large (N ≈ 8.4) to be relevant to transition in low-disturbance environments. It is shown that excitation of dominant modes F and S occurs in a small vicinity of the plate leading edge. The initial disturbance propagates further downstream in accord with the two-mode approximation model accounting for the mean-flow nonparallel effects and the intermodal exchange mechanism. This computationally economical model can be useful for predictions of the second mode dominated transition onset using the physics-based amplitude method. [ABSTRACT FROM AUTHOR]

The present study investigates a novel control strategy to create a sweeping oscillatory jet using fluidic actuation principle. A supersonic underexpanded primary jet issued into a suddenly expanding duct is oscillated by giving cyclic pulsed secondary jet blowing in the top and bottom step regions of the suddenly expanding duct. The current study employs the bistable nature of jet expansion seen in a suddenly expanding duct for the jet oscillation. The cyclic perturbations (pulsed secondary jet blowing) given in the streamwise direction switch the direction of the asymmetric jet expansion of the underexpanded primary supersonic jet to the top and bottom wall alternatively, thereby creating an oscillatory supersonic jet. It is found that the switching of the direction of the primary jet to any one wall is caused by the Coanda effect produced by the secondary jet issued in the corresponding wall side. The results show that the primary jet quickly responds to the secondary jet perturbations and that the supersonic primary jet oscillation frequency nearly matches secondary jet perturbation frequency. A parametric study to investigate the jet oscillation characteristics with various secondary jet oscillation frequencies and mass flow rate ratios are also being carried out in the present study. It is found that the jet oscillation frequency increases with increase in the secondary jet pulsation frequency. The jet deflection is found to increase with increase in the secondary jet to primary jet mass flow ratio (blowing ratio) up to a critical limit, after which the increment in jet deflection ceases due to the restrictions imposed by the duct geometry. [ABSTRACT FROM AUTHOR]

U-shaped sonic booms associated with the dive maneuver of a supersonic vehicle are numerically simulated in this paper. Usual prediction tools for ordinary sonic booms are not suitable for such a waveform because of the breakdown of geometrical acoustics near the caustic. In this paper, nonlinear Tricomi equation approach is used near the caustic to take diffraction into account, whereas augmented Burgers equation analysis is applied away from the caustic where geometrical acoustics is applicable. The U-shaped waveforms predicted by this method are in good agreement with measured data. The effects of atmospheric turbulence are also considered by replacing one-dimensional analysis using augmented Burgers equation with multidimensional wave propagation analysis near the ground surface. Results with the atmospheric turbulence effects show better agreement with measured U-shaped waveform than ones without such effects. It is also found that the amplitude of the tail shock wave, which is much larger than the front shock wave, is more sensitive than the front shock to atmospheric turbulence. [ABSTRACT FROM AUTHOR]

In this study, the aerodynamic characteristics of the three-dimensional evacuated tube transportation (ETT) system based on the Reynolds-averaged Navier–Stokes κ−ω shear-stress transport turbulent model were investigated. The effects of two key parameters on the drag and flow topology of the ETT system, namely the travelling speed and ambient pressure in the tube, were studied. Compared with trains in the atmospheric environment without the tube (i.e., the open system), the ETT system shows considerable drag reduction with suitable operating parameters in the tube, particularly at a higher travelling speed range. The drag varying with the speed from subsonic to supersonic, shows various change trends at different speeds because of their distinct flow structures. The higher pressure in front of train head was observed to be reduced by choking, and a low pressure in the wake by expansion waves led to rapid increase in the drag and drag coefficient. The relationship between the drag and operating pressure was observed to be approximately linear for both the subsonic and supersonic speeds. [ABSTRACT FROM AUTHOR]

Experimental research has been carried out of the processes occurring in a three-flow vortex tube operating in the humid air. Two types of swirling devices are investigated: single-pass spiral (snail) and multi-entry of five curved channels. An increase in the isentropic efficiency of a multi-entry swirling device by an average of 45% for a cold flow in the region μ = 0.10 ... 0.8 in comparison with a snail one has been experimentally confirmed. Three positions of the dividing gap were investigated at a distance of 4, 5, and 6 mm from the nozzle inlet. The drying efficiency of a snail-type swirling device is 10–15% better, and moisture removal through the separator is 10–25% better in comparison with a multi-entry swirling device. The vortex velocity distribution profiles are determined numerically using the SST turbulence model. It was revealed that an increase in the vortex velocity in the area of the swirling device by 15% made it possible to obtain an increase in the isentropic efficiency by 50%. A hypothesis has been put forward describing the mechanisms that realize the effect of breaking of liquid particles inside a vortex tube, which can reduce the efficiency of liquid separation by up to 25%. • A three-flow vortex tube is an effective device for the moisture separation. • Design parameters makes a significant influence on the vortex tube operation. • Multi-entry swirling ensures supersonic speed of the flow inside the vortex tube. • Multi-entry swirling provides 45% higher efficiency comparing to simple snail-type one. [ABSTRACT FROM AUTHOR]