Diaphragm Pressure Ratio Research Articles

A Study on the interaction of shock tube-generated blast waves with a circular object at different pressure ratios

The interaction of high peak overpressure blast waves with a circular object placed at two different axial locations from the shock tube exit is studied through numerical simulation using an in-house developed multi-component Navier–Stokes solver. The driver and driven sections of the shock tube were 0.8 m and 6 m, respectively. Helium is used in the driver section, while atmospheric air is used in the driven section and outside the shock tube. The evolution of blast waves inside an open-ended shock tube and its interaction with a rectangular object is reported in Murugan et al.. (2022). Here, the blast wave interacting with a circular object is examined for diaphragm pressure ratios of 13 and 57 by placing the objects at 250 mm and 500 mm from the shock tube exit. The flow field is evaluated through numerical Schlieren, vorticity, density, pressure plots, and the enstrophy plot, which shows the vortical structures that originated in the flow field. The blast load acting on the circular object is calculated for two diaphragm pressure ratios and axial locations. This study helps understand the reflection and diffraction of blast waves and associated flow fields around circular objects used in blast wave attenuation.

Physical mechanism for prolonged test duration in shock tubes

The main challenge in the operation of shock tubes is the very short test time. Hence, this work was carried out to optimize the ratio of driver section to driven section length and to investigate its effect on the test time in a shock tube. Three different cases were tested in this paper for driver to driven tube length ratio of 2, 1, and 0.5. The study was conducted numerically using ANSYS Fluent CFD solver and k-epsilon realizable turbulent model. The shock wave strength and speed were monitored at two different locations downstream the driven tube for diaphragm pressure ratio of 10. The numerical model was verified with experimental measurements in a shock tube apparatus at the College of Engineering, Universiti Tenaga Nasional, Malaysia (UNITEN). From the numerical and experimental data, the primary shock strength was very comparable, while using low pressure ratio of 10. Subsequently, higher pressure ratio of 20 and 30 were implemented and the results were compared to select the longest test time. A driver section to driven section ratio of 2 resulted in a longer test time of approximately of 20 ms. In addition, insignificant reduction in the test duration of about 5 % was observed after increasing the driver tube pressure to 30 kPa. In contrast, higher peak pressure was recorded for pressure ratio of 30 for all three cases.

A Study of Shock-Induced Transient Jets: The Impact of Exit Conditions on Mach Disk and Vortex Ring

Abstract We investigate the effect of exit pressure history on the flow characteristics of underexpanded transient jets. Using both experiments and numerical simulations, we study the dynamics of shock-cell and vortex structures within these jets. A shock tube with an open-ended configuration allows us to generate transient jets by adjusting the diaphragm pressure ratio and the length of the driver section. Our results indicate that when the shock Mach number exceeds 1.6, a Mach disk forms, indicating a highly underexpanded transient jet at the exit of the shock tube. A distinguishing feature of this jet is the emergence of counter-rotating vortex rings (CRVRs) alongside the initial primary vortex ring. Our findings reveal a substantial influence of both the amplitude and duration of the peak exit pressure on the characteristics of the Mach disk and vortex ring. Notably, the characteristics of the primary vortex ring exhibit significant sensitivity to the formation and evolution of CRVRs. In cases of continuously decreasing exit pressure, the Mach disk follows a consistent self-similar decay pattern, regardless of the peak exit pressure magnitude. Finally, we present an empirical relationship between exit pressure and the characteristics of the Mach disk. In summary, this research provides insight into the complex interaction between the exit pressure history and the flow characteristics in underexpanded transient jets.

Numerical simulation of high peak overpressure blast wave through shock tube and its interaction with a rectangular object

The generation of high peak overpressure (>10 bar) blast wave inside the shock tube and its interaction with a rectangular object is examined in this paper using the in-house developed multi-component Navier–Stokes solver. It is difficult to generate these peak overpressure blast waves in the laboratory due to aerodynamic noise and strong reflected blast waves. Driver and driven section lengths of the shock tube are 0.8 m and 6 m respectively. A blast wave with a non-dimensional peak overpressure of 11.65 is generated inside the shock tube using helium as the driver section gas with a diaphragm pressure ratio of 57. The peak overpressure and pressure histories obtained from simulations are validated with shock tube experiments and found to be matching closely. Next, the development of a strong trailing jet after diffraction of the blast wave at the shock tube exit is studied. Finally, the interaction of blast wave with a rectangular object is studied using numerical schlieren images, line plots of pressure and density.

An experimental and numerical investigation of the effects of the diaphragm pressure ratio and its position on a heated shock tube performance

AbstractThe main purpose of this work was to investigate the performance of heated shock tube (ST) with different pressure ratios and diaphragm positions numerically and experimentally. The numerical model was developed to simulate the fluid flow inside a shock tube test facility located at Qatar University. The shock tube was a cast‐iron hollow tube with 6 m length, 50 mm internal diameter and 10 mm thickness. ST driver and driven sections were filled with helium–argon mixture and air. The driven section was heated up to 150°C using coils. At the middle of the ST, the diaphragm was made of aluminium sheet (0.5 mm) layers. Five different pressure ratios were implemented during the experiment, and performance evaluation depended on the strength of the incident shock Mach number. The inviscid numerical model solver used transient two‐dimensional time‐accurate Navier–Stokes CFD. The model introduced a parametric study regarding three different diaphragm positions (1m, 2m and 3m) and five pressure ratios (6–10) for each position. In addition to yielding the incident and reflected wave Mach number, reflected wave temperature was also considered a shock tube performance indicator. The incident Mach numbers for the diaphragm middle position from the experiment were compared against those conducted from the model, and good matching was observed. The parametric study results showed that at high‐pressure ratios, diaphragm Positions 1 and 3 could generate a 7.4% increase in shock wave Mach number compared with the diaphragm position‐2 model. Moreover, the diaphragm position‐3 model tends to have a 2% increase in the temperature behind the reflected shock wave compared with the other two positions.

A comparative study on the evolution of compressible vortex ring generated from a short driver section shock tube

The compressible vortex ring emanating from an ultra-short driver section shock tube is simulated using Euler and Navier–Stokes solvers for a diaphragm pressure ratio of 8.4. The numerical results are compared with smoke flow visualization experiments performed in a shock tube. Here the main focus is to compare the vortex ring evolution during its self-sustained motion as many researchers studied the vortex ring dynamics during its formation and growth stage. It is observed that the formation and interaction of Kelvin–Helmholtz (K-H) vortices generated at the trailing jet make the flow distinct in the solvers and experiments though the shock cell structures, embedded shock, and counter-rotating vortices are similar. Surprisingly in simulations, the vortex ring has regained its compact structure after its strong interactions with K-H and counter-rotating vortices. Whereas, it becomes a turbulent structure during its self-sustained motion in experiments. Further, the vortex ring simulated through a viscous solver moves downstream with a higher translational velocity compared to the inviscid solver at the later stage. The translation velocity of the vortex ring is the least in experiments and it may be attributed to the strong turbulent viscosity compared to the physical viscosity.

Performance evaluation of shock tube with helium and carbon dioxide using numerical simulation

This work deals with the performance of the shock tube with helium and carbon dioxide as working fluids at different diaphragm pressure ratios using numerical simulation. A two-dimensional planar geometry of the shock tube is considered for the study. An inviscid time accurate model is developed to find the effects of diaphragm pressure ratios on the shock Mach number, temperature behind the incident and reflected shocks.. This numerical model is validated analytically as well as experimentally with air as working gas. Simulations were conducted for same and different driver/driven gas combinations with helium and carbon dioxide test gases using this model. Simulations were carried out using CFD solver FLUENT. Adaptive Mesh Refinement (AMR) technique was applied to accurately capture and resolve shock and contact discontinuities. At lower pressure ratios the different gas model is able to produce 20.4% and at higher diaphragm pressure ratios up to 33% increase in shock Mach number when compared to the similar driver-driven gas model.

Numerical Visualization of Blast Wave Interacting with Objects

Blast wave interaction with objects has gained attention due to military conflict and terrorist attack across the globe. Blast wave attenuating and mitigating structures are needed to be developed to protect the military vehicles and commercial buildings. In order to understand the attenuating mechanism such as the dissipation and dispersion along with the secondary effects, the blast wave interacting with three objects is examined in the present study for the diaphragm pressure ratio of 56. Here, the blast wave is generated in a short driver section open ended shock tube by solving the Euler equations using the commercial software ANSYS Fluent. It has been observed that the circular disc attenuates the blast wave more effectively compared to the cone and sphere for the same frontal area. The attenuation was lowest in the sphere and maximum in the circular disc. However, the loads acting on the sphere was more compared to the conical object. The peak load acting on the circular disc was 2.09 times more compared to the peak load acting on the conical object (cone angle 26.5°) with the same hydraulic diameter.

CFD Modelling of Flow Characteristics in Micro Shock Tubes

The use of micro shock tubes has become common in many instruments requiring a high velocity and temperature flow field, for example in micro-propulsion systems and drug delivery devices for medical systems. A shock tube has closed ends, and the flow is generated by the rupture of a diaphragm separating a driver gas at high pressure from a driven gas at relatively low pressure. The rupture results in the movement of a shock wave and contact discontinuity into the low-pressure gas, and an expansion wave into the high pressure gas. The characteristics of the resulting unsteady flow for micro shock tubes are not well known as the physics of such tubes includes additional phenomena such as rarefaction and complex viscous effects at low Reynolds numbers. In the present study, computational fluid dynamics (CFD) calculations are made for unsteady compressible flow within a micro shock tube using the van-Leer MUSCL scheme and the two-layer k-e turbulence model. Novel results have been obtained and discussed of the effects of using different diaphragm pressure ratios, shock tube diameters and wall boundary conditions, namely no slip and slip walls.

Numerical simulation of flow characteristics in micro shock tubes

Recently micro shock tubes have been widely used in many engineering and industrial fields, but the characteristics of unsteady flow are not well known to date in micro shock tubes. Compared to conventional shock tubes with macro scales, flows related to shock waves in micro shock tubes are highly complicated. Stronger viscous and dissipative interactions make shock wave dynamic behaviors significantly different from theoretical predictions. In the present study, a CFD work was applied to the unsteady compressible Navier-Stokes equations which were solved using a fully implicit finite volume scheme. The diaphragm pressure ratio and shock tube diameter were varied to investigate their effects on micro shock tube flows. Different wall boundary conditions were also performed to observe shock wave and contact surface propagation with no slip and slip walls. Detailed flow characteristics at the foot of shock wave and contact surface propagation were known from the present numerical simulations.

Numerical simulation of shock wave and contact surface propagation in micro shock tubes

Micro shock tubes have been widely used in many engineering and industrial applications, but their performance and detailed flow characteristics are not well known. Compared to macro shock tubes, unsteady flows related to the moving shock waves in micro shock tubes are highly complicated due to more active viscous dissipation and rarefaction effects. This makes shock wave dynamics significantly different from theoretical predictions. One of the major flow behaviors related to the shock wave propagation in micro shock tube is that the boundary layer growth leads to stronger dissipative shock wave. Due to effects of the scale, more shock wave attenuation happens in micro shock tubes. We used a CFD approach to understand the flow characteristics in a micro shock tube with finite diameter. A fully implicit finite volume scheme has been employed to solve the unsteady compressible Navier-Stokes equations. The diaphragm pressure ratio and diameter of the shock tube were varied to investigate their effects on micro shock tube flows. Based on the predicted results, some wave diagrams were built to characterize the micro shock tube flows. Detailed flow structures between the contact surface and moving shock wave were analyzed during the present study.

Effect of viscosity and wall heat conduction on shock attenuation in narrow channels

In the present work, the effects due to viscosity and wall heat conduction on shock propagation and attenuation in narrow channels are numerically investigated. A two-dimensional viscous shock tube configuration is simulated, and heat conduction in the channel walls is explicitly included. The simulation results indicate that the shock attenuation is significantly less in the case of an adiabatic wall, and the use of an isothermal wall model is adequate to take into account the wall heat conduction. A parametric study is performed to characterize the effects of viscous forces and wall heat conduction on shock attenuation, and the behaviour is explained on the basis of boundary layer formation in the post-shock region. A dimensionless parameter that describes the shock attenuation is correlated with the diaphragm pressure ratio and a dimensionless parameter which is expressed using the characteristic Reynolds number and the dimensionless shock travel.

Experimental Study of Unsteady Flow in a Shock Tube for Needle-Free Drug Delivery

Recently, the needle-free delivery system has been widely used in medical fields due to its convenience in delivering drug particles into human body without any external needles. In order to penetrate through the outer layer of the skin, drug particles need to obtain enough momentum, which is achieved by accelerating drug particles in a Contoured Shock Tube (CST). The CST consists of a micro shock tube with two diaphragms and an expanded supersonic nozzle. In the present study, experimental studies were carried out by pressure measurement. Six high sensitive pressure transducers were used for recording pressure changes as the shock wave moved through different locations along walls in the test section. From which, data on shock wave propagation could be obtained. Different diaphragm pressure ratios were conducted to demonstrate effects of initial diaphragm pressure ratios on shock wave propagation. Shilieren visualization was also performed to observe shock wave propagation and shock wave structure in the present experimental shock tube model. The characteristic of the internal flow and shock wave system have been studied and analyzed in details in the present shock tube model.

The effects of area contraction on the performance of UNITEN's shock tube: Numerical study

Numerical study into the effects of area contraction on shock tube performance has been reported in this paper. The shock tube is an important component of high speed fluid flow test facility was designed and built at the Universiti Tenaga Nasional (UNITEN). In the above mentioned facility, a small area contraction, in form of a bush, was placed adjacent to the diaphragm section to facilitate the diaphragm rupturing process when the pressure ratio across the diaphragm increases to a certain value. To investigate the effects of the small area contraction on facility performance, numerical simulations were conducted at different operating conditions (diaphragm pressure ratios P4/P1 of 10, 15, and 20). A two-dimensional time-accurate Navier-Stokes CFD solver was used to simulate the transient flow in the facility with and without area contraction. The numerical results show that the facility performance is influenced by area contraction in the diaphragm section. For instance, when operating the facility with area contraction using diaphragm pressure ratio (P4/P1) of 10, the shock wave strength and shock wave speed decrease by 18% and 8% respectively.

English

This paper presents an experimental investigation into the effects of area contraction on shock wave strength and peak pressure in a shock tube. The shock tube is an important component of the short duration, high speed fluid flow test facility, available at the Universiti Tenaga Nasional (UNITEN), Malaysia. The area contraction was facilitated by positioning a bush adjacent to the primary diaphragm section, which separates the driver and driven sections. Experimental measurements were performed with and without the presence of the bush, at various diaphragm pressure ratios, which is the ratio of air pressure between the driver (high pressure) and driven (low pressure) sections. The instantaneous static pressure variations were measured at two locations close to the driven tube end wall, using high sensitivity pressure sensors, which allow the shock wave strength, shock wave speed and peak pressure to be analysed. The results reveal that the area contraction significantly reduces the shock wave strength, shock wave speed and peak pressure. At a diaphragm pressure ratio of 10, the shock wave strength decreases by 18%, the peak pressure decreases by 30% and the shock wave speed decreases by 8%.

Compressible Flow Structures Interaction with a Two-Dimensional Ejector: A Cold-Flow Study

An experimental study has been conducted to examine the interaction of compressible flow structures such as shocks and vortices with a two-dimensional ejector geometry using a shock-tube facility. Three diaphragm pressure ratios of P 4 /P 1 = 4, 8, and 12 have been employed, where P 4 is the driver gas pressure and P 1 is the pressure within the driven compartment of the shock tube. These lead to incident shock Mach numbers of M, = 1.34,1.54, and 1.66, respectively. The length of the driver section of the shock tube was 700 mm. Air was used for both the driver and driven gases. High-speed shadowgraphy was employed to visualize the induced flowfield. Pressure measurements were taken at different locations along the test section to study the flow quantitatively. The induced flow is unsteady and dependent on the degree of compressibility of the initial shock wave generated by the rupture of the diaphragm.

Compressible vortex loops: Effect of nozzle geometry

Vortex loops are fundamental building blocks of supersonic free jets. Isolating them allows for an easier study and better understanding of such flows. The present study looks at the behaviour of compressible vortex loops of different shapes, generated due to the diffraction of a shock wave from a shock tube with different exit nozzle geometries. These include a 15 mm diameter circular nozzle, two elliptical nozzles with minor to major axis ratios of 0.4 and 0.6, a 30 × 30 mm square nozzle, and finally two exotic nozzles resembling a pair of lips with minor to major axis ratios of 0.2 and 0.5. The experiments were performed for diaphragm pressure ratios of P 4 / P 1 = 4 , 8, and 12, with P 4 and P 1 being the pressures within the high pressure and low pressure compartments of the shock tube, respectively. High-speed schlieren photography as well as PIV measurements of both stream-wise and head-on flows have been conducted.

Numerical investigation of micro shock waves generation

The shock wave propagation in the micro channel of the different sizes is studied numerically in order to estimate the possibility of the experimental apparatus development. The full compressible Navier–Stokes equations are used for the numerical simulation. The shock wave velocity attenuation is found for the channel height smaller than H = 200 μm. The influence of the channel size and of the diaphragm pressure ratio on the shock wave velocity is considered. The considerable influence of the viscous effects on the shock propagation is shown.

Analysis of unsteady wave processes in a rotating channel

AbstractThe impact of passage rotation on the gasdynamic wave processes is analyzed through a numerical simulation of ideal shock‐tube flow in a closed rotating‐channel containing a gas in an initial state of homentropic solid‐body rotation. Relevant parameters of the problem such as wheel Mach number, hub‐to‐tip radius ratio, length‐to‐tip radius ratio, diaphragm temperature ratio, and diaphragm pressure ratio are varied. It is shown that for a fixed geometry and initial conditions, the contact interface acquires a distorted three‐dimensional time‐dependent orientation at non‐zero wheel Mach numbers. At a fixed wheel Mach number, the level of distortion depends primarily on the density ratio across the interface and also the hub‐to‐tip radius ratio. The nature of the rarefaction and shock wave propagation is one‐dimensional, although the acoustic waves are diffracted due to the radially varying propagation speed. Under conditions of initially homentropic solid‐body rotation, a degree of similarity exists between rotating and stationary shock‐tube flows. This similarity is exploited to arrive at an approximate analytical solution to the Riemann problem in a rotating shock‐tube.

Boundary layer flows behind constant speed shock waves moving into a dusty gas

Laminar boundary layer flows behind constant speed shock waves moving into a dusty gas are analyzed numerically. The basic equations of two-phase flows are derived in shock fixed coordinates and solved by an implicit finite-difference method for the side wall boundary layer in a dusty gas shock tube. The development of the boundary layer and resulting velocity and temperature profiles, respectively, for the gas and particles are given from the shock front to far downstream. The effects of diaphragm pressure ratio, mass loading ratio of particles and particle size upon the flow properties are discussed in detail.