Innovative Aerospace Solutions
We're designing a new 200kg VTOL drone, but have hit a problem with wing-propeller interaction. We need someone to help us understand
the issues - and then to help us scope out the range of solutions that are available to us.
Compendium of Results
The slides below summarise a few findings of potentially more general interest that we have extracted from our work on various projects* for various clients - we hope you find them interesting!
Pressure distribution on the surface of the Skylon vehicle when flying hypersonically at high
altitude, comparing the predictions of a Direct-Simulation Monte Carlo method and the Hyflow
reduced-order model.
More information
The Skylon spaceplane is intended to launch from a runway and to accelerate into space using a hybrid rocket-airbreathing propulsion system. Once having delivered its payload into orbit, the vehicle glides back to a landing at the same airport from which it took off. Although somewhat eclipsed by recent advances in more conventional rocketry, the premise of such a vehicle is that its unique mode of operation could make access to space cheaper and more routine than traditional expendable rocket technology.
One of the major design challenges is to create a configuration that, on re-entering the earth's atmosphere, can dissipate the very large energy associated with an orbital vehicle without overheating, but at the same time can have good enough aerodynamic performance to be able to glide all the way back to its launch site. The solution adopted by Skylon is to minimise the heating by pitching the vehicle nose-up to present its flat underbelly to the flow during the high-speed portion of the re-entry, and then to return to a more level attitude to continue its glide to its landing site with an aerodynamic efficiency that is similar to that of a slender supersonic transport aircraft.
Analysis and optimisation of the performance of such a vehicle requires thousands of evaluations of its aerodynamic characteristics at various points along its trajectory. Traditional methods of aerodynamic analysis based on the Navier Stokes or Boltzmann equations are just too slow in such applications, often requiring hours or even days to produce a single data point. Our Hyflow methodology makes use of the Newtonian Flow approximation to give very rapid predictions of the aero-thermodynamics of hypersonic vehicles compared to these more conventional approaches - indeed, predictions take seconds rather than hours.
Of course speedy but inaccurate predictions are of little use to anybody. The figure shows a comparison, conducted as part of the verification of the simpler model for use in optimising the re-entry trajectory of Skylon and similar vehicles, of Hyflow's predictions of the pressure distribution over the surface of Skylon (when operating at high altitude and Mach number in its nose-high mode) to similar results obtained using the Direct Simulation Monte Carlo approach.
The principal differences between the predictions are relatively localised in extent - for instance, Hyflow, in not modelling explicitly the positions of the shock waves in the flow, misses features in the pressure field such as the small patch of elevated pressure where the shock that is produced upstream of the nacelle interacts with the outboard part of the wing. Despite these localised discrepancies in prediction, the integrated loads on the airframe - in terms of lift, drag and moment about the centre of gravity - turn out to be very similarly predicted by both approaches.
Since it is these integrated loads that have direct effect on the dynamics of the vehicle, the aerodynamic predictions of the simpler model are usually accurate enough for a design-level determination of the best control strategy to adopt during re-entry into the earth's atmosphere. A series of initial simulations using Hyflow would be used to provide the basis for a more in-depth optimisation of the vehicle's characteristics, particularly of its heating (which is very much more directly dependent on proper resolution of localised features in the flow - such as those that are induced by shock-body interactions!) using more sophisticated methodologies once the design space had been properly explored and the simpler approach had been used to isolate a small set of promising solutions for closer study.
* Except where explicit permission has been obtained to release actual data, geometries and test conditions have generally been changed to protect the intellectual property of the sponsors of the original work.
Use the tab above to access the latest news from Sophrodyne Aerospace!
The tab above leads to a page containing various articles on aeronautical topics that we have written over the last years.
These are in addition to Dr Brown's published academic articles, a list of which can be found here.
The tab above leads to a page containing some simple tools and downloads that may be of use to you in performing your own investigations.
Sophrodyne's Fundamental Approach
Our years of experience in combining numerics and theory lies at the core of Sophrodyne's way of working. We understand that an analysis of a problem using a brute force approach (such as is obtained for example with a pre-packaged general-purpose CFD code) is often necessary and useful in order to obtain basic data - for instance for evaluating a parameter or to validate a model - and we have the tools to do that.
We believe though that this approach only becomes cost-effective and valuable once these individual data are abstracted into a sensible mathematical framework which clearly expresses one's current understanding of the problem. Unlike "ideas" or "hunches", an explicit, simple mathematical model is a tangible object with which the human intellect can engage and interact. A good model allows the strength of your understanding of the problem to be exploited directly in being able to predict the properties of the system that are of interest to you. But often even more important is the fact that predictive errors in the same model are very often an indication of a deficiency somewhere in understanding the problem properly. The key advantage thus of the model-building process during the development of a product is that it invariably promotes the sort of interaction with the problem in which these lapses in understanding can be exposed and rectified before they can cause too much harm.
This is where the experienced practitioner will save you time and effort in achieving your goals.
We understand from first principles the methodologies that underpin most current commercial aerodynamic tools, and can advise regarding both their strengths and their weaknesses. In many instances we have our own analogue methodologies that we have written in-house and understand down to the last line of code. We can use these to perform genetically-independent sanity checks on, and independent verifications of, the data coming out of your models, or to perform the relevant analyses on your behalf. Indeed, over the years we have built up a series of models that work from very limited data to give reliable estimates of the most salient performance characteristics of a wide range of flight vehicles - from subsonic drones and helicopters, through mid-sized commuter aircraft, through to supersonic jets and even hypersonic re-entry vehicles!
We can also help you upgrade and develop your internal modelling capabilities, starting from a clean sheet of paper or based on what you already have available. You may be surprised to find out how broadly used our methodologies are within the aerospace community.
Most importantly, and this is where we specialise in bringing value to organisations such as yours, we can help you understand and generalise your proprietary data into models that can be used over and again, not only today but also in your future products, adding to your reserve of intellectual property and know-how as you develop your product line.
Please feel free to contact us to discuss your problems and requirements.
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