Abstract: Flows over a square cylinder of side length D with and without a splitter plate at a
Reynolds number of 150 is numerically investigated. The length of the splitter plate is
varied systematically from L = 0.5D to L = 6D so the sensitivity of the flow structure
to the inclusion of the splitter plate can be inspected. It is found that the splitter plate
introduces a strong hydrodynamic interaction to the near wake of the cylinder and the
length of the plate has a significant effect on how the flow structure changes. For short
plate lengths (0 < L < D), the free shear layers are convected further downstream when
the plate length is increased, which is the first flow regime observed. For intermediate
plate lengths (1.25D < L < 4.75D), a secondary vortex is clearly visible around the
trailing edge of the splitter plate, indicating the second observed flow regime. For long
plate lengths (L >= 5D), a third flow regime is observed in which the free shear layers
reattach to the splitter plate. The study also examines various length scales, based
on a variety of wake parameters, to investigate the possibility of a universal Strouhal
number. A near universal Strouhal number is found for (0 < L < 4D) when the
minimum wake half-width is used.
Abstract: This paper presents experimental data concerning the flow and noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number (Reynolds number based on chord of 2.0 × 105 to 5.0 × 105). The data are used to evaluate a variety of semi-empirical trailing edge noise prediction methods. All were found to under-predict noise at lower frequencies. Examination of the velocity spectra in the near wake reveals that there are energetic velocity fluctuations at low frequency about the trailing edge. A semi-empirical model of the surface pressure spectrum is derived for predicting the trailing edge noise at low-to-moderate Reynolds number.
Abstract: This paper investigates the unsteady, near wake of a circular cylinder in cross flow at a Reynolds number of 5.5 x 10^3 using Large Eddy Simulation (LES). The near and intermediate wake velocity fields and unsteady aerodynamic forces compare well against available experimental data. Flow visualisation results show the presence of intermittent Kelvin Helmholtz (KH) instabilities in the very near wake. An empirical relation is presented for the spanwise length scales associated with KH instability that compares favourably with LES data. A wavelet analysis technique is used to investigate the frequency content of near wake. This analysis shows the existence of vortex pairing and breakdown in the near wake, providing further evidence that the near wake shear layer behaves in a similar manner to a mixing layer.
Abstract: An ecient stochastic method is applied to the problem of mod-
eling unsteady turbulent velocity
uctuations within a turbulent
at
plate boundary layer. White noise is spatially and temporarily con-
voluted by the time averaged Reynolds stress tensor and dissipation.
The convolutions are conducted such that mean turbulent properties
are reproduced and the spectral distribution of turbulent kinetic en-
ergy closely matches expected pro les. Wall bounded turbulent flow
induces elevated levels of broadband aeroacoustic noise, especially near a sharp edge such as an airfoil trailing-edge. In practise, the stochastic method of generating turbulent
fluctuations may be used directly to produce turbulent noise sources for further aeroacoustic analysis,
thus avoiding costly time-dependent simulations of the Navier-Stokes equations.
Abstract: A new method for calculating the aerodynamic noise generated by bluff bodies is presented in this paper. The methodology uses two-dimensional, Unsteady Reynolds Averaged Navier Stokes turbulent flow simulations to calculate the acoustic source terms. To account for turbulent flow effects that are not resolved by the flow simulation, a statistical approach has been developed and applied to introduce narrow band random noise. Spanwise decorrelation of flow information is accounted for using a correction method based on a decorrelation length scale. Curle's compact acoustic analogy is used to calculate the far-field noise. To illustrate the effectiveness of the method, the turbulent flow and noise about a cylinder is calculated and compared with experimental results from the literature.
Abstract: A computationally efficient, quasi-one-dimensional supersonic combustion ramjet
(scramjet) propulsion model has been produced for use in hypersonic system
design studies. The model solves a series of ordinary differential equations using
a 4th order Runga-Kutta method, to describe the gas dynamics within the
scramjet duct. Additional models for skin friction and wall heat transfer are also
included. The equations are derived assuming an open thermodynamic system
with equilibrium or simplified chemistry combustion models. The combustion is
also assumed to be mixing rather than kinetically limited. This assumption allows
simplification of the modelling and is justified when the model is compared against
experimental results. Three test cases are used to validate the performance of the
scramjet propulsion model: (1) modelling a reflected shock tunnel hydrogen fuelled
scramjet experiment, (2) a continuous flow hydrogen fuelled scramjet ground
test and (3) a segment of the HyShot II flight test. The results show that the
model simulates scramjet propulsion with a reasonable degree of accuracy.
Abstract: A theoretical, experimental and numerical study is presented of the interaction of a vortex wake created by an upstream blade with a downstream prismatic block. The aim of the study is to investigate the fundamentals of force and noise generation for this type of flow and explain how inter-object spacing affects the far-field noise level. A theoretical model, based on a compact form of Curle's formulation, is developed and shows that acoustically constructive or destructive interference is determined by the amplitude and phase of the forces on each object as well as the Strouhal number. Experimental and two-dimensional, unsteady numerical results of the vortex wake interaction case are presented for several blade-block separation distances. Using a combination of this experimental and numerical data, the theoretical model is able to explain observed variations in far-field noise level with blade-block separation distance. The numerical model accurately predicts the phase relationship between the unsteady forces on each object. Numerical flow visualisation shows that this phase difference is controlled by the aerodynamic interference effects caused by the downstream block.
Abstract: BLUFF bodies are integral components of aircraft, high-speed
trains, automobiles, and many forms of industrial equipment.
The minimization of mean and fluctuating force levels generated by
bluff bodies when placed in a fluid stream has the benefits of reducing
drag, vibration, and radiated sound. It is therefore very important that
a good understanding of the flowfield about bluff bodies be obtained
to achieve these aims. This Note explores how low Reynolds number
bluff-body wake interference can affect the generation of unsteady
flowand force. The case chosen for study is the interaction of a square
cylinder and an infinitely thin flat plate.
Abstract: If technology such as aircraft, submarines and wind turbines are to further reduce their noise emissions, then a better understanding of airfoil trailing edge noise is required. This paper will discuss the physical causes of trailing edge noise and then review the methodologies used over the past couple of decades to model and estimate TE noise. A comprehensive reference list is given for readers wishing to learn more about this important area of aeroacoutsics. It is shown that one of the major restrictions to further development of prediction methods is a lack of suitable experimental data for validation purposes. Additionally, new turbulence models are needed to improve noise prediction, especially at high frequency.
Abstract: A potential flow and viscous flow solver have been coupled to produce a robust computational tool useful for the design of low speed wind tunnel contractions. After validation against published numerical and experimental wind tunnel data, the method is used to evaluate recently proposed contraction shapes from the literature. The results show that, on balance, a 5th order polynomial provides a good design solution. Newly proposed shapes will either improve available flow area at the expense of contraction outlet flow uniformity or vice-versa.
Abstract: The performance of a conceptual, missile class, hypersonic vehicle was modeled using a 2 degree-of-freedom dynamics model. The vehicle was assumed to be air-launched, accelerated to a Mach number of 3 using a solid propellant rocket and subsequently propelled using a dual-mode scramjet engine to cruise at Mach numbers between 4 and 9. Modeling results show that fuel storage capacity and dynamic pressure have a significant effect on vehicle range and average speed. A perturbation analysis was also performed that ranked the sensitivity of missile range to small changes in 14 design parameters. The kinetic energy efficiency (total pressure loss) of the scramjet has the highest effect on performance at high cruise Mach numbers (6.7-9), followed by structural mass, combustion efficiency and aerodynamics parameters. At low cruise Mach numbers (4-6.7), structural concerns dominate performance, followed by the aerodynamics and scramjet operating parameters.
Abstract: This paper compares the performance of the scramjet powered stages of two different launch systems; one using a hydrogen fuelled scramjet stage and one using a hydrocarbon fuelled scramjet stage. The two launch systems are optimized with respect to payload delivery capability and then compared, assuming a fixed launch mass. A rocket powered booster is used to achieve the required scramjet ignition conditions and a rocket powered orbital stage is used to accelerate the payload from scramjet shut-down to low earth orbit. The trajectory simulator includes a full spheroidal, rotating earth model, a fourth order gravitation model and an MSISE93 atmosphere model. A gradient projection optimization routine is used to achieve an optimal solution using a set of time referenced vertical accelerations as optimization parameters. Hypersonic engine performance is determined using a quasi-one-dimensional scramjet model. Results show that a hydrogen powered scramjet launch system outperforms a hydrocarbon powered system due to its higher specific impulse and peak Mach number. While payload mass fractions are shown to be favorable, the high structural requirements of the scramjet imply that reusability is a key characteristic to make them financially viable. Trajectories were found to be dominated by their lift requirements, which outweighed any performance advantage for hydrocarbon fuels in terms of their better storage capability.
Abstract: The interaction of bluff bodies in an air flow can generate high sound pressure levels.
Especially for the interaction of the cylinder/plate-configuration the generated noise can
be amplified enormously by the insertion of a plate behind a cylinder. In this work the
aeroacoustic sound generation of a cylinder/plate-configuration has been investigated ex-
perimentally. The amplification of the generated sound is quantized and the condition for
the amplification is analyzed in detail. In the experiments the distance between cylinder
and plate as well as the flow velocity were varied. A critical spacing that depends on the
flow velocity was found, for which the sound pressure levels rise dramatically. The vari-
ation of the distance and the flow velocity also showed a hysteresis effect regarding the
occurrence of the sound pressure amplification.
Abstract: This paper presents an acoustic analysis of the noise generated at the trailing edge of a flat plate encountering low
turbulence fluid flow. Experimental measurements were taken in an anechoic wind tunnel using four microphones:
one mounted above the trailing edge, one below the trailing edge, one adjacent to the trailing edge and one above the
leading edge. The noise spectra produced by the flat plate were recorded at the four microphone locations. Information
about the strength and directivity of the trailing edge noise is determined by comparing the four signals. Subtracting the
out-of-phase signals at the microphones above and below the trailing edge is shown to increase the airfoil self-noise
spectra further above that of the ambient noise and is shown to be an effective signal extraction technique.
Abstract: The aim of the present study is the assessment of advanced EASM turbulence models
and hybrid RANS/LES methodologies for predicting the hydrodynamic eld of the NASA
tandem cylinder con guration. Simulations are performed with the nite volume code
OpenFOAM using a k-!-EASM model, a Partially-Integrated-Transport-Model (PITM)
and a modi ed Flow-Simulation-Methodology (FSM). A grid convergence study is con-
ducted in order to assess the sensitivity of the results to the spanwise length of the domain
and the cell count in the spanwise direction. Acoustic predictions are obtained using an
acoustic analogy based on Curle's theory. It was found that the grid re nement is eec-
tive in reducing the surface pressure
uctuations on the upstream cylinder. However, no
consistent improvement in results were observed for the grid re nement study. The FSM
approach predicts results in very good agreement with reference data. The PITM and
EASM approaches both predict too intense vortex shedding, which is primarily re
ected in
the mean velocity distribution and in the predictions of turbulent kinetic energy. Acoustic
predictions were found to give very good agreement about the main tone while de ciencies
exist in accurately predicting the secondary peaks due to drag and higher harmonics.
Abstract: The performance of several novel hybrid RANS/LES methodologies for accurate flow and noise predictions of the NASA Tandem Cylinder Experiment are investigated. Simulations are performed using three different hybrid RANS/LES methodologies which employ different techniques to transform the baseline RANS model into a turbulence resolving subgrid scale model. The approaches investigated are the Scale-Adaptive-Simulation which computes the subgrid dissipation-rate from a transport equation that is sensitive to the v. Karman length scale, the IDDES approach and a modified Flow-Simulation-Methodology (FSM) which both rely on replacing the modeled turbulent length scale with a measure of the local grid spacing. Since we expect that the predictions in the RANS and LES region depend on the capabilities of the baseline RANS model, the hybrid RANS/LES approaches used in this study are based on an Explicit-Algebraic-Stress Model. These models are assessed and compared with formulations based on a traditional two-equation model.
The simulations are performed with the open-source finite volume code OpenFOAM and acoustic predictions are obtained using an acoustic analogy based on Curle's theory. The IDDES and FSM approaches were found to predict the hydrodynamic field in very good agreement with reference data but showed some deficiencies in capturing the higher harmonics in the acoustic spectra and broadband noise levels at high Strouhal numbers. The SAS appraoches lack in accuracy for prediciting the hydrodynamic field but resolve the higher harmonics in the acoustic spectra.
Abstract: A sinusoidal modification to the leading edge of an airfoil (tubercles) has led to the
elimination of tonal noise for a NACA 0021 airfoil at a Reynolds number, Re ~ 120,000. It
has also been found that the overall broadband noise is reduced for a considerable range of
frequencies surrounding the peak in tonal noise. Investigations have also revealed that
changing the amplitude and spacing between the tubercles has an effect on noise reduction.
The mechanism of noise reduction is believed to be strongly related to the formation of
streamwise vortices which are generated by tubercles. These vortices most likely have an
effect on the stability characteristics of the boundary layer, hence influencing the velocity
fluctuations of the shear layer near the trailing edge. In addition, spanwise variations in
separation location are thought to affect the vortex shedding process, which could influence
the feedback mechanism.
Abstract: The generation of aeolian tones by the interaction of a low Reynolds number, low Mach number flow with a rigid
square cylinder attached to a rigid thin flat plate is numerically investigated. When the length of the plate is varied
from L = 0:5D to 6D, where D is the side length of the square cylinder, the results can be grouped into three distinct
regimes. For the first regime (L . D), the aeolian tone levels decrease with increasing plate length. For the second regime
(2D . L . 4D), the aeolian tone levels are always higher than the single square cylinder case and they increase with
increasing plate length. For the third regime (5D . L . 6D), the levels of the aeolian tones decrease as the length of the
plate increases but the levels are higher than the other regimes. These acoustic results can be explained in terms of the
fluid mechanics occurring in the near wake of the cylinder.
Abstract: A new computational aeroacoustic model suitable for the prediction of turbulent airfoil trailing edge noise is presented. The method (known as the RANS based Statistical Noise Model or RSNM) combines numerically generated, mean turbulence information with a Green's function for a semi-infinite half-plane to generate a far-field acoustic auto-spectrum. As a preliminary application of the method, the acoustic spectrum created by turbulent flow past the sharp trailing edge of a flat plate at a Reynolds number ($Re$) of $5.5\times10^5$ is calculated. Four different turbulence models are used to provide the required mean flow data which is used with RSNM. The predicted spectra are shown to agree well with a semi-empirical model from the literature.
Abstract: The NASA Tandem Cylinder experiment has been simulated for the case where the cylinders were placed 3.7 diameters apart (center-to-center). This configuration allows vortex shedding to occur in the inter-gap region between the cylinders. Two-dimensional, unsteady Reynolds averaged Navier Stokes flow simulations were performed using the OpenFOAM open source code. Simulated mean and unsteady flow results compare well with published experimental data. The major discrepancies between numerical and experimental flow results can be attributed to neglecting the spanwise velocity component during simulation. Acoustic computations were made using two-dimensional flow data and a compact form of Curle's theory with spanwise and temporal statistical models that introduced random perturbations into the time-domain signals. The upper and lower frequency limits of the acoustic simulation method were selected using arguments based on acoustic compactness and an estimate of near-field acoustic effects. Acoustic simulation results compare well with experiment about the main tone. Further improvements are necessary to broaden tones at the harmonics.
Abstract: This paper describes a systematic method of refining a
computational grid for the Direct Numerical Simulation
(DNS) of flow about a square cylinder. The grid
refinement method involves two stages. The first stage
constructs computational meshes based on reasonable
estimates of cell size and grid stretching ratios and
investigates the sensitivity of the computed flow field to
these parameters. The findings from this stage are used as
a guide for further grid refinement. In the second stage, the
grid is divided into four regions to minimise the grid
stretching ratio. The smallest cell is sized so the boundary
layer on the front face of the cylinder is adequately
resolved. Solutions on seven different grids are presented
to investigate the effect of numerical scheme, boundary
conditions and grid independence. The level of grid
independence is evaluated using a form of Richardson
extrapolation and the study shows that the finest grid
solution has a grid Convergence Index (GCI) of less than
5%.
Abstract: A theoretical description of a fuel-air mixing loss model is derived from first principles and placed within a quasi-one-dimensional scramjet combustor code. This code is then compared with experimental and multidimensional computational fluid dynamics results from the literature. Quasi-one-dimensional results compare well against published data and show that this approach is suitable for conceptual design and vehicle performance studies. Results also show that total pressure loss due to fuel-air mixing is about the same magnitude as losses due to friction. The performance of a generic, full scale scramjet using both hydrogen and hydrocarbon fuels, over a flight Mach number range of 5-15 is then investigated. Thrust loss due to skin friction and mixing are shown to be significant.
Abstract: This paper will discuss a method of bluff body noise control that utilises the phenomenon of aerodynamic interference. This technique uses a second body (not necessarily bluff) that is placed in the wake of the bluff body whose noise we wish to control. Through proper understanding of the wake dynamics, the amplitude and phase of the noise from the downstream body can be controlled so as to achieve noise reduction in the far-field. This paper will present a theoretical model of noise reduction via aerodynamic interference based on the theory of Curle. The noise from a two-dimensional square cylinder will be then assessed numerically with and without a flat plate placed within its wake. The results show that the presence of the downstream body creates a high level of non-linear interference that needs to be understood in detail before effective noise reduction can occur.
Abstract: The mixing of a passive scalar in the wake of a slightly heated cylinder has been studied numerically by coupling the Unsteady Reynolds Averaged Navier Stokes (URANS) equations with a scalar transport equation and a turbulent-scalar transport model for a Reynolds number of Re = 3900. The URANS method is shown to capture key features of the flow field and passive scalar fluctuations in the near wake. However, the excessive dissipation associated with the turbulence model interferes with the near wake flow and scalar spectra. Therefore caution must be exercised when using URANS methods to model applications involving scalar mixing behind bluff bodies.
Abstract: A computationally efficient, quasi-one-dimensional supersonic combustion ramjet propulsion model has been produced for use in hypersonic system design studies. The model uses a series of ordinary differential equations, solved using a 4th order Runge-Kutta method, to describe the gas dynamics within the scramjet duct. Additional models for skin friction and wall heat transfer are also included. The equations were derived assuming an open thermodynamic system with equilibrium or simplified chemistry combustion models. The combustion was also assumed to be mixing rather than kinetically limited. This assumption allows simplification of the modeling and was found to be justified when the model was compared against experimental results. Three test cases are used to validate the performance of the scramjet propulsion model: (1) modeling a reflected shock tunnel hydrogen fuelled scramjet experiment, (2) a continuous flow hydrogen fuelled scramjet ground test and (3) a segment of the HyShot II flight test.
Abstract: The interaction of a helicopter’s main rotor tip vortex with the tail rotor is an important source of noise and vibration, yet it is still poorly understood. An important limiting case is the orthogonal blade vortex interaction (OBVI) where a three-dimensional vortex structure is cut by the tail rotor blade. It has been discovered that the blade unsteady surface pressures during OBVI are controlled by the tip vortex axial flow component. Recent aerodynamic testing of the OBVI confirming this result is reviewed along with a description of an anechoic wind tunnel for aero-acoustic OBVI research. The design of a new wind tunnel contraction and a single bladed rotor rig are also discussed.
Notes: Presented at the 6th Australian Vertiflite Conference on Helicopter Technology, 12th Au
Abstract: A potential flow and viscous flow solver have been coupled to produce a robust computational tool useful for the design of low speed wind tunnel contractions. A validation study was successfully performed and it is shown that the computational model compares favorably with experimental and numerical results from the literature. The flow solver was then used in a numerical optimization methodology using a two parameter contraction shape defined by a Bezier curve with aim of producing optimal contraction designs. The objective function and constraints used in the optimization are described, and a visualization of the objective function over the feasible region shown. Three methods, Sequential Quadratic Programming (SQP), DIRECT and Efficient Global Optimization (EGO) have been used to optimize the contraction shape. SQP was able to solve the optimization problem efficiently, but not robustly. DIRECT provided a robust global optimization at the expense of function evaluations. EGO is robust and always gave acceptable solutions, but its efficiency depended on the initial random sampling. In some cases it was competitive with SQP, and with further research should become an attractive algorithm for global optimization of low speed wind tunnel contractions.
Abstract: This work reports on the use of numerical optimisation techniques to optimise objective functions calculated by Computational Fluid Dynamics (CFD) simulations. Two example applications are described, the first being the shape optimisation of a low speed wind tunnel contraction. A potential flow and viscous flow solver have been coupled to produce a robust computational tool, with the contraction shape defined by a two parameter Bezier curve. The second application is a simplified test case with a known minimum calculated using a commercial CFD code.
For the optimisation of complex CFD simulations, it is sometimes advantageous to use an efficient derivative free global optimisation algorithm because of potentially long simulation times, the objective function may contain multiple local minima and it is often difficult to evaluate analytical or numerical gradients. The Efficient Global Optimisation (EGO) algorithm sequentially samples results from an expensive calculation, does not require derivative information, uses an inexpensive surrogate to search for a global optimum, and is used in this current work.
For both applications, the EGO algorithm is able to efficiently and robustly find a global optimum that satisfies any constraints.
Abstract: After more than half a century of intense activity and the considerable development of
complex numerical models, aeroacoustic research still relies heavily on experimental
approaches. Experimental data is essential to provide reference data for fundamental test
cases, to understand highly complex and interacting phenomena, and to validate numerical
simulations. At the University of Adelaide, the School of Mechanical Engineering is
undertaking the upgrade and optimisation of its small-scale wind tunnel to support its
increasing research activity in aeroacoustics. An experimental programme to start in 2007
requires a quiet 75 x 300 mm2 rectangular cross-section jet with a maximum flow speed of 30
m/s, in an enclosure that is anechoic at frequencies above 200 Hz. This paper gives a brief
outline of the process followed to upgrade the wind-tunnel, including the air supply system,
flow treatment and jet cross-section. Additionally, the flow properties and acoustic
performance of the wind tunnel are measured assessed through a series of validation
experiments, and the main results are presented here against the initial design objectives. The
results of a simple experiment consisting of a cylinder in cross-flow are also presented to
indicate performance as a demonstration of tunnel performance during aeroacoustic testing.
Initial results are compared with a semi-empirical model to demonstrate the performance of
the wind tunnel. Finally, a brief outline of the subsequent research work to be carried out in
the wind tunnel is given.
Abstract: The wake of a blunt airfoil has been analysed using a two-dimensional \underline{U}nsteady \underline{R}eynolds \underline{A}veraged \underline{N}avier \underline{S}tokes (URANS) method. The $k-\epsilon$, Spalart-Allmaras and \underline{P}artially \underline{R}esolved \underline{N}avier \underline{S}tokes (PRNS) turbulence models were compared along with experimental data. All three models were able to successfully reproduce the effect of vortex shedding on the thickness of the boundary layer at the trailing edge. However, the simulations do not show as good a comparison in the near-wake region of the airfoil, due to an over prediction of the velocity defect in all cases. The Spalart-Allmaras model provided the best prediction of the intermediate- wake region. The PRNS model persistently underestimates the centreline wake velocity in the intermediate wake.
Abstract: A new performance model was developed for hydrocarbon fuelled (Jet A) scramjet
powered hypersonic systems. It was applied to air-launched hypersonic missile concepts
that were boosted to a specified Mach number (3) and dynamic pressure (40-100 kPa)
using a solid propellant rocket motor. After boost, a dual-mode airbreathing supersonic
ramjet engine accelerates the missile concept along a constant dynamic pressure, ballistic
trajectory until it reaches a prescribed cruise Mach number (4-9). The performance model
integrates the equations of motion over the entire mission and therefore takes into account
variations in aerodynamic trim due to fuel consumption. Results show that fuel storage
capacity has significant effect on vehicle range and average speed. A sensitivity study was
also performed that investigated the effects of changing 14 design parameters on overall
range. It was shown that the kinetic energy efficiency (entropy gain) of the propulsion
system had the highest affect on performance followed by structural mass, combustion
efficiency and aerodynamics parameters.
Abstract: This paper compares the performance of two
different launch systems; one with a hydrogen fuelled
scramjet stage and one with a hydrocarbon fuelled scramjet
stage. The two launch systems are optimized with respect to
payload delivery capability and then compared, assuming a
fixed launch mass. A rocket powered booster is used to
achieve the required scramjet ignition conditions and a
rocket powered orbital stage is used to accelerate the payload
from scramjet shut-down to low earth orbit.
The trajectory simulator includes a full spheroidal, rotating
earth model, a fourth order gravitation model and an
MSISE93 atmosphere model. A gradient projection
optimization routine is used to achieve an optimal solution
using a set of time referenced vertical accelerations as
optimization parameters. Hypersonic engine performance is
determined using a quasi-one-dimensional scramjet model.
Results show that a hydrogen powered scramjet launch
system outperforms a hydrocarbon powered system due to
its higher specific impulse and peak Mach Number. While
payload mass fractions are shown to be favorable, the high
structural requirements of the scramjet imply that reusability
is a key characteristic to make them financially viable.
Trajectories were found to be dominated by their lift
requirements, which outweighed any performance advantage
for hydrocarbon fuels in terms of their better storage
capability.
Abstract: Modelling the complete chemical kinetics and flow physics of
supersonic combustion is a complex task that requires
considerable computational resources. To develop
performance evaluation tools for future hypersonic vehicles,
accurate yet computationally efficient solution methods are
required. In this work, a supersonic flame model is derived
and used in a quasi-one-dimensional internal flow solver to
provide simulations of experimental scramjet ground tests.
The results show that the technique is capable of modelling
the pressure rise along a scramjet combustor in a
computationally efficient manner. The results are of sufficient
accuracy for the method to be used for hypersonic vehicle
evaluation and performance studies.
Abstract: This paper investigates the performance benefits of using scramjet propulsion to accelerate a second stage satellite launch vehicle to Mach 14. A two-stage solid rocket booster is used to achieve the required scramjet ignition conditions and another rocket stage is used to accelerate the payload from scramjet shut-down to orbital conditions. The lifting acceleration is used as a control parameter to develop a trajectory, which achieves the required target conditions. A trajectory simulator is described, which includes a full spheroidal, rotating earth model, a fourth order gravitation model and an MSISE93 atmosphere model. A fourth order Runge-Kutta integration routine is used to integrate the trajectory. From both a gross lift-off mass and a propellant consumption point of view, a part scramjet powered vehicle is seen to have a significant performance advantage over a totally conventional rocket powered vehicle.
Notes: (9 Pages, CD Proceedings ISBN: 0 86459 3740).
Abstract: A multiple combustor pulse detonation engine concept is
analysed using a fourteen species chemical equilibrium model.
Results are coupled with an analytical two-dimensional
supersonic inlet model to provide estimates of operational
performance. The analysis provides preliminary engine sizing
and operational information of hydrocarbon fuelled pulse
detonation engines for future tactical missile systems and boostphase
propulsion for hypersonic air-breathing engines.
Abstract: The fluid dynamics and acoustic emission that occurs when a flat plate is placed in the near wake of a square cylinder has been studied numerically. First, a two-dimensional direct numerical simulation (DNS) about a single square cylinder at $Re=150$ was performed and validated against available experimental and numerical data. Using an analytical model of sound generation and DNS data, the optimal location and size of a 2D infinitely thin flat plate for the minimisation of far-field sound was determined. A second DNS was then performed for this cylinder-plate arrangement in order to assess the effectiveness of the plate. The near wake interaction with the flat plate altered the shedding frequency cylinder along with other fundamental properties of the flow. The near wake flow is completely changed and shows many new and interesting features. Despite far-field noise emitted by the cylinder being reduced by 15.3~dB, the total far-field sound was reduced by only 3.63~dB, as the downstream plate generated an aerodynamic force almost four times that of the cylinder. In addition, the convective properties of the cylinder wake were significantly changed by the plate, thus reducing its ability to reduce noise by appropriate phasing of unsteady aerodynamic forces. In order to find the optimal size and location of a noise reducing plate, multiple DNS need to be performed in order to take into account all non-linear flow interactions. A recommendation of this report is to study the square cylinder-plate interaction in more detail, as many new and previously unobserved flow features are present.
Notes: This is a paper/report of my work at Chalmers in May/June 2008.
