Sidewall Mass Injection Research Articles

Turbulent Flow Characteristics in a Model of a Solid Rocket Motor Chamber with Sidewall Mass Injection and End-Wall Disturbance

The present analytical, numerical, and experimental investigations are performed to study the flow field in acoustically simulated solid rocket motor (SRM) chamber geometry. The computational solution is carried out for a high Reynolds number and low Mach number internal flows driven by sidewall mass addition in a long chamber with end-wall disturbances. This kind of flow (transient, weakly viscous, and contains vorticity) have several features in common with a turbulent flow field. The numerical study is performed by solving the unsteady Reynolds-averaged Navier–Stokes equations along with the energy equation using the control volume approach based on a staggered grid system. The v2-f turbulence model has been implemented in the current study. A comparison of the SIMPLE and PISO algorithms showed that both algorithms provide identical results, and the computational time using the PISO algorithm is higher by about 6% than the corresponding value of the SIMPLE algorithm. A fair agreement has been obtained between the numerical, analytical, and experimental results. Moreover, the results showed that the complex turbulent internal flow patterns are induced inside the chamber due to the strong interaction of the sidewall injection with the traveling acoustic waves. Such a complex internal structure is shown to be dependent on the piston frequency and sidewall mass flux. The current study, for the first time, emphasizes the acoustic-fluid dynamics interaction mechanism and the accompanying unsteady rotational fields along with the effect of the generated turbulence on the unsteady vorticity and its impact on the real burning rate.

Interactions between turbulent flow and diffusion flame of composite propellant in a solid rocket motor with sidewall mass injection

The numerical procedure for a diffusion flame based on Ammonium Perchlorate/Hydroxyl-Terminated Polybutadiene (AP/HTPB) composite propellant in a solid rocket motor (SRM) is presented. This article accounts for the turbulence effects in a combustion chamber with sidewall mass injection and the propellant diffusion flames at various axial locations are studied. The mutual coupling between the vortical and entropy modes is discussed comprehensively, with the inclusion of the influence of the chamber pressure. The effects of the AP particle size and the combustion environment are also analyzed. The flow evolution in the SRM is clearly observed in the results: laminar, transitional, and turbulent. Compared with the laminar area, the flames fluctuate drastically in the turbulent flow, and the chemical kinetics processes are altered greatly. The diffusion and mixing processes of the reactants are enhanced due to the contribution of the turbulence, and the heat release of the flames is elevated. The high chamber pressure and smaller AP size could lead to more intensive fluctuations of the flame heat release. This may drive thermoacoustic instability in the SRM.

Entropy Generation through Non-Equilibrium Ordered Structures in Corner Flows with Sidewall Mass Injection

Additional entropy generation rates through non-equilibrium ordered structures are predicted for corner flows with sidewall mass injection. Well-defined non-equilibrium ordered structures are predicted at a normalized vertical station of approximately eighteen percent of the boundary-layer thickness. These structures are in addition to the ordered structures previously reported at approximately thirty-eight percent of the boundary layer thickness. The computational procedure is used to determine the entropy generation rate for each spectral velocity component at each of several stream wise stations and for each of several injection velocity values. Application of the procedure to possible thermal system processes is discussed. These results indicate that cooling sidewall mass injection into a horizontal laminar boundary layer may actually increase the heat transfer to the horizontal surface.

Investigations of Turbulence Generation in a Model of Solid Rocket Motor Chamber with Sidewall Mass Injection and Endwall Disturbance

The present paper presents numerical investigations of the internal flow field in a nozzleless solid rocket motor chamber with compressible transpiration and endwall disturbance. More attention is given for predicting the induced turbulent flow inside the chamber. The considered physical configuration of the nozzleless solid rocket motor consists of a two-dimensional rectangular and porous chamber fitted at the head end with a specifiedfrequency-oscillating piston and it is opened to atmospheric plenum in the downstream direction. The numerical study is performed by solving the unsteady RANS equations along with the energy equation using the control volume approach on the basis of a staggered gridsystem. Different two-equation turbulence models have been implemented and their accuracy is estimated through a comparison with the available experimental measurements. A fairly general agreement has been obtained between the numerical and the experimental results. Moreover, the obtained results showed that complex turbulent internal flow patterns are induced inside the chamber due to the strong interaction of the sidewall injection with the traveling acoustic waves. Such complex internal structure is shown to be dependent on piston frequency and sidewall mass flux.

Rotational and Quasiviscous Cold Flow Models for Axisymmetric Hybrid Propellant Chambers

In this work, we present two simple mean flow solutions that mimic the bulk gas motion inside a full-length, cylindrical hybrid rocket engine. Two distinct methods are used. The first is based on steady, axisymmetric, rotational, and incompressible flow conditions. It leads to an Eulerian solution that observes the normal sidewall mass injection condition while assuming a sinusoidal injection profile at the head end wall. The second approach constitutes a slight improvement over the first in its inclusion of viscous effects. At the outset, a first order viscous approximation is constructed using regular perturbations in the reciprocal of the wall injection Reynolds number. The asymptotic approximation is derived from a general similarity reduced Navier–Stokes equation for a viscous tube with regressing porous walls. It is then compared and shown to agree remarkably well with two existing solutions. The resulting formulations enable us to model the streamtubes observed in conventional hybrid engines in which the parallel motion of gaseous oxidizer is coupled with the cross-streamwise (i.e., sidewall) addition of solid fuel. Furthermore, estimates for pressure, velocity, and vorticity distributions in the simulated engine are provided in closed form. Our idealized hybrid engine is modeled as a porous circular-port chamber with head end injection. The mathematical treatment is based on a standard similarity approach that is tailored to permit sinusoidal injection at the head end.

Vorticity generation and acoustic resonance of simulated solid rocket motor chamber with high wave number wall injection

An asymptotic technique is integrated with computational solution development to describe the generation and evolution of intense unsteady vorticity and the accompanying temperature response in a model of solid rocket motor (SRM) chamber with low Mach number, weakly viscous internal flow. The chamber considered here has a rectangular cross-section, has to equally permeable walls, closed at the head end, and is opened at the downstream end. An initially steady internal flow from steady sidewall injection is generated. Then an additional transient sidewall mass injection with different wave numbers at non-resonance and resonance frequencies is imposed on the generated steady one. This mechanism is used to simulate the transient propellant combustion occurring on the sidewall in a real SRM chamber. The analytical approach is based on the reduced form of the Navier–Stokes using asymptotic technique. The results show that unexpectedly large transient shear stresses and temperature gradients are created at the sidewall of the chamber at resonance frequencies and low wave numbers. A comparison between the analytical, computational and experimental results is performed.

Premixed edge-flame oscillations in a rectangular channel with side-wall mass injection

The steady structures and the dynamics of oscillatory motions of strained, premixed edge-flames are studied in a planar rectangular channel, closed at one end, with side-wall mass injection. The injection velocities are either constant or temperature-flux dependent. The motivation for this study is recent experiments conducted by Berghout et al (2000 Proc. Combust. Inst. 28 911–7) in a rectangular crack of a homogeneous propellant. The strained edge-flame dynamics are obtained by numerical solution of the zero-Mach-number, variable density Navier–Stokes equations, assuming a one-step reaction. Important parameters are found to be the Reynolds number Re based on the injection velocity and surface separation, the Lewis number Le, and the strain-dependent Damköhler number. We show the first theoretical illustration of edge-flame oscillations in a premixed environment, which are found to occur in near-limit conditions, induced, for example, by decreasing the mass injection surface separation distance leading to an increase in the characteristic strain rate, and for sufficiently large Lewis numbers. A marked difference between oscillatory edge-flame structures with constant and temperature-flux dependent injection conditions is also found.M This article features multimedia enhancements available from the supplemental page in the online journal.

Three-dimensional flow in a cylinder with sidewall mass addition

Three-dimensional, time-dependent, nonlinear flow dynamics within a cylinder with sidewall mass injection are investigated. A nonaxisymmetric transient injection velocity, prescribed along the sidewall boundary of a long, narrow, half-open cylinder, induces a low Mach number, high Reynolds number flow. The injection drives nearly planar axial acoustic disturbances, which interact with the injected fluid to produce the azimuthal component of vorticity on the sidewall in an inviscid manner. A smaller, but important azimuthally dependent transient disturbance, driven by the nonaxisymmetric injection disturbance leads to the axial component of vorticity on the cylinder sidewall. Both components of vorticity are shown to convect toward the center of the cylinder, diffuse radially, and convect downstream. Other results show that the axial component of vorticity produced along the sidewall is largest near the maximum of a mass source distribution in the azimuthal dimension. The amplitude of the axial vorticity component decreases significantly away from the injection surface and at other azimuthal locations. The analysis of these flow processes is based on the full three-dimensional Navier–Stokes equations. A formal multiple-scale asymptotic analysis, based on the behavior of the axial Mach number M→0, is used to derive reduced equations. It is shown that the primary rotational flow response is described by a nonlinear, convection-diffusion equation.

Acoustically generated unsteady vorticity field in a long narrow cylinder with sidewall injection

Asymptotic and computational analyses of a well-posed initial-boundary-value problem are used to describe the time history of co-existing acoustic and rotational velocity disturbances in a long, narrow cylinder with uniform steady sidewall mass injection. Transient planar pressure disturbances prescribed on the open exit plane of the cylinder are the source of acoustic disturbances in the axisymmetric flow. Both the asymptotic and numerical solutions describe the nonlinear aspects of the flow interactions. The full computational results are compared favorably with those of the asymptotic study to show that; (1) transient vorticity is generated near the injection surface and is transported into the cylinder by the radial velocity component of the flow field, (2) at any sufficiently small value of time, a well defined front separates the fluid containing transient vorticity from a flow field in the interior of the cylinder containing a much smaller amplitude vorticity and, (3) at sufficiently large values of time, vorticity is present throughout the cylinder. In addition, the analytically derived acoustic solution obtained from the asymptotic analysis is used to show that the present numerical solution and all earlier studies of similar problems are missing travelling waves (eigenfunctions) which should be present in a complete mathematical solution of the defined initial-boundary-value problem.

Coexisting acoustic-rotational flow in a cylinder with axisymmetric sidewall mass addition

Time-dependent flow dynamics within a cylinder with sidewall mass injection are investigated. A time-dependent injection velocity, prescribed along the sidewall boundary of a long, narrow, half-open cylinder, induces a low Mach number, high Reynolds number flow. The injection is the source of planar acoustic disturbances which interact with the injected fluid to produce vorticity on the sidewall in an inviscid manner. The analysis of these flow processes is based on the Navier–Stokes equations, which are reduced to simpler forms using a multiple-scale asymptotic analysis. The equations that arise from the analysis describe the leading-order vorticity dynamics. These nonlinear equations possess both wave and diffusion properties and are solved in an initial value sense. The results show that the vorticity produced at the sidewall convects toward the center of the cylinder, diffuses radially, and convects downstream.

Acoustic waves over a transpiring surface

An investigation of the effect on the acoustic waves due to wall mass injection in a piston-driven closed-end test chamber has been conducted. Dry ice is used as a source of mass injection. Acoustic pressure is measured with a pressure transducer mounted at the closed end. A comparison with the results with no side wall mass addition shows a significant increase in the acoustic pressure amplitude due to the interaction of the acoustic wave and side wall mass injection near resonance. A shift in the lowest resonant frequency between the two cases has also been detected. High-speed flow visualization and hot wire anemometry measurements all suggest that turbulence may occur in the acoustic boundary layer above the transpiring surface. This, in turn, feeds more energy into the acoustic wave. This increase in amplitude has never been reported before to the authors' best knowledge. [Work supported by U.S. Air Force Astronautics Laboratory and Morton Thiokol, Inc.]