Ralph Holland obtained the degrees: B Sc, Dip Ed, Dip Com Sc with formal training in Aerodynamics, Astronomy, Classical and Quantum mechanics, Chemistry, Computing, Computer Simulation, Electronics, Thermodynamics, Solid State Physics, Mathematics and Education, and has held the following professional memberships: MIEEE, MACM, and MACS.
Ralph is a trained glider and power plane pilot with over 1500 hours of power plane experience operating under a PPL working towards a CIR. This is very current experience for Ralph started gliding in 2004 and obtained his PPL in 2005 and purchased his first aircraft 20 Jan 2006 at 260 hrs total time.
Ralph is a keen computer simulator, and of particular interest is computational simulation and verification of models.
Ralph's professional career has lead to the development of many real-time system software, including: message-interchange protocols; real-time Kalman filters; real-time highly-concurrent Geographic Information Systems; Ship, Aircraft and Radar Simulation systems; and follows the development of Computational Fluid Dynamics and just how the models are currently ineffective at modeling Wind Turbine Wake fields.
Wind Turbine Wake is a combination of a Blade-tip votices, Hub and Axial Turbulence and its expansion, Pressure Turbulence through the blades, and the consequential Velocity Deficit due to power extraction, all of which tends to be contained in a Plume-like structure, and is blown down stream via the wind. Hence we have termed Wake Plume to collectively describe the phenomena.
It is these Wake Plumes that are made visible in opportunistic photographs such as the above image of Horns Rev, or indeed the video of the Cullerin Range Windfarm Windmills in the Mist where you can see a tortuous void in the clouds behind each turbine.
These Wake Plumes have been compared to aircraft wing-tip vortices or wake, however, although both turbine blade tip vortices and wing-tip vortices are the result of aerodynamic forces, and although they might be considered similar they are not due to a very fundamental difference; in the aircraft case the vortices are generated by the aircraft movement relative to the air, whereas in the wind-turbine case the turbine hub is fixed in space and it is the air that is moving and the entire turbine blade assembly is rotating extracting energy from the air and imparting torque forces on the air as a result encasing the phenomena in its entirety within a vortex sheath spanning the blade-diameter, with the inside of the wake containing a velocity deficit and reduced pressure. It is the free-air velocity (or the wind) that is always present during the process and causes the entire wake to propagate downstream, and on the evidence of the photographs shows the extent of propagation as being extensive, with the divergence being relatively small i.e. the Plume propagates for some distance before it dissapates.
When determining a safe distance from a wind tubine and its Wake Plume to aviation infrastructure a precautionary approach must be taken under the law, and the worst case scenario must be taken into account, covering the poorest aircraft performance and the worst case wind, and in particular consideration must be given to the lightest aircraft, such as ultra-lights, and unpowered flight such as sail-plane gliders, hang-glider, para-glider and indeed the parachutist. Of particular note is that aircraft are most vulnerable when they are travelling at low speed, such as during the take-off and landing phases, should they encounter the wind-shear and turbulence of enough magnitude to stall a wing and cause an uncommanded roll (wing-drop or tipping) of the aircraft that they may have insufficient time to recover, and in the case of unpowered flight one cannot recover with power - it is not an option. The effect on helicopters may also involve uncommanded pitching moments as well as uncommanded yaw and roll.
The arguments must be based on safety of life, reasonable expectations of safeguarding life, precaution and care. Not only may a proponent, land owner, and approving authorities be culpable under Common Law Torte they may also be found culpable under the Criminal Code:
We have brought what we believe to be an Aviation Hazard to the awareness of CASA and to our politicians, by way of the Senate, it is now up to the controlling authorities to uphold their legal duty of care to ensure that wind farms and the Wake Plume are not a hazard on a case-by-case basis, until they enact legislation with a determination of a safe-distance and buffer zones so it is clear to all proponents just what rules they are operating under; it is inadequate to leave this to the state authorites as no two authorites are consistent, making it commercially difficult for the wind farm proponents. What is required is clearly defined legislation with clearly defined boundaries.
A word of caution: Computational Fluid Dynamics models have been found to inadequately explain the Wind Turbine wake; until experimental validation verify any model the model must be taken to be a guide only, until such time as models pass the experimental validation we cannot trust that they provide adequate guidance when the situation involves safety of life. It is also inadequate to conduct subjective flight trials in light wind, what we need to know is the morphology of the Wake Plume and what it looks like in the worst case wind conditions. This is why we have called for a proper scientific study to be made to Profile the Wake Plume using LIDAR, and one which can be performed behind existing wind farms to map the magnitude and extent of the turbulence and velocity deficit within the Wake Plume.
Until such time as this occurs objectively, we are calling for a 50 blade-diameter setback of wind turbines from aviation infrastructure (based on the extrapolation of experimental data to date), where infrastructure includes the circling area of an aerodrome, registered or unregistered, and any known area of aviation activity, such as parachuting, and manned-gliding in all its forms. We have even extended this to ensure that land-based wind turbines are setback from the shore so their wake plumes cannot disrupt sailing. We believe adhering to this policy, based on information we have to date, that a proponent would be deemed to be in compliance with their duty of care by any reasonable person.
Our windfarm policy.
Turbine data at hand shows blade-disk diameters between 90 and 164 metres and wind cutoff speeds of between 22 to 25 m/s (42.8 to 48.6 Kts), and maximum revolutions limited to between 4.5 to 20.7 rpm. The larger turbines tend to be limited to 17 to 19 rpm, with the 164 m Vestas turbine being limited to 12.1 rpm. The maximum blade tips speeds have been calculated as varying between 141 to 202 Kts. More manufacturer turbine data may be required to refine these parameters, but given a reasonably proficient search it is not unreasonable to be performing Wake Plume safety analysis at operating wind speeds of 24 - 30 Kts and one can argue that studies should be done over the whole range from the cut in speed all the way to cutoff speeds, and on a case by case basis, because each turbine is different. One would also expect that at their most efficient operating wind speed that they are operating near the Betz condition of wind speed behind the blades being 1/3 of the windspeed in front of the blades, as then Cp would be at its most efficient.
These speeds are also not unreasonable speeds for we often see 25 to 30 Kts of wind speed at the wind sock level and due to progressive wind shear we expect that the wind speeds will be greater at the wind turbine hub and blade tip heights, you only have to look at the rated wind-speeds to determine what the turbine manufacture expects is normal.
The velocity deficit expected within a Wake Plume is from 2/3 down to 1/3 of the free-flow velocity, depending on the location within the Wake Plume, and when the turbine is operating near the Betz peak Cp. With turbines operating within normal wind speeds of 24 to 30 Kts close to the Betz condition of optimim Cp. the velocity deficit may constitute a windshear of 16 to 20 Kts which needs to be compared with aircraft Vs and 1.3 Vs0 in the landing phase. (e.g. a Mooney M20J Vs0 = 53, Vat = 68.9 and the wind-shear would result in an effective speed of 52.9 to 48.9 Kts which is below the aircraft stall speed Vs0; the same can be calculated for other aircraft, the lower Vs the worse is their susceptibility when flying at Vat e.g. C182 Vs0 = 43 Kts, C172 Vs0 = 42 Kts, C150 Vs0=35.)
Since wind turbine parameters such as Ct, Cp and turbulence have been found to be related to Tip speed ratio, and turbulence is inter-related to wind speed, any study should examine the Wake Plume under varying conditions of wind speed and blade tip speed ratios, as well as blade disk diameters, to comprehensively characterise the Wake Plume profiles. (See Aeordynamics of Wind Turbines by Martin O. L. Hansen.)
Wind Turbines and models, as well as manufacture are wide and varied; the following table provides an example of some of the available models, of note is the range of operating conditions such as cut in and cutoff wind speeds and the maximum revolution limit.
|Manufacturer||Model||Blade disc Diameter m||Number of blades||Tower height metres||Rated Power MW||Cut In wind speed m/s||Rated Wind speed m/s||Cutoff Wind Speed||Min rpm||Maximum rotation revs per minute||Max revs per second||blade disk circumference m||Max tip speed m/s||Max tip speed Knots||Wind Operating Speed Kts||Cutoff Wind Speed Kts|
Galion animation of real data from a UK windfarm showing turbine wake plume velocity deficit and turbulence.
Note latest news is first ...
20120110: Are we imagining Wind Turbine Wake Plumes? No we are NOT; scroll up to see the above image which was sourced from the Galion website.
These setbacks have been called due to blade fragmentation and ice throw, and it is interesting to see just how far the fragments have been seen to travel. Although this setback is less than what we need for aviation, the reports and investigations are still important findings Permitting Setbacks for Wind Turbines in California and the Blade Throw Hazard.
20121213: The CASA FOI material was received. The material report was a risk analysis, and the accompany emails show that only the turbine physical height and placement was being treated as an obstruction. No consideration has been given to the Wake Plume. More on this as I analyse the risk report. One gets the feeling that the authorities totally discregard wake Plumes - despite the photographs and evidence.
20121106: Concerning my FOI request on CASA dated the 19 Oct, at this time (6 Nov) I had not received any FOI material or further correspondence, with the deadline I assumed being the 10 Nov, 30 days from my application, in accordance with the act.
20121108: I received the FOI response Refusal on Practical Grounds despite wanting the material on the basis of public safety. So now the request needs to be revised, I am sure I could have been advised of this far sooner than 27 days, is this an example of bureacratic delaying? I am not after private material, I am after a report concerning safety hazard aspects of wind turbines and one that hopefully has findings regarding a safe distance from turbines. I am hopeful that the legal contact officer may be able help me hone in on this material, rather than have to wait for an aviation incident. Or is this another case of "affordable safety" that CASA keeps speaking of?
I knew I have seen this somewhere, "Safe Skies for All" - look at the motto on the CASA Practical Refusal response, be prepared ... this might be another case of Affordable Safety. One would reckon with some degree of confidence that Affordable Safety is not an argument within CASA from their OH&S department; when one of their officer hurts themselves in the course of their work e.g. cutting a finger on their filing cabinet, a report would surely be filed? Would the safety of an aircraft, a pilot and their passengers be any less important I ask? Affordable Safety - watch out for this phrase and count how many times it occurs.
Here is my response to the practical refusal
20121109: CASA reconsiders the FOI request CASA response in response to the above correspondence.
20121109: Things are not going well with the Department of Infrastructure and Transport, they have not produced any evidence or expertise nor authority to have committed the department to the: official response in question.
20121113: The CASA FOI request is now unblocked and time is ticking 10 days from the 14 Nov: CASA confirmation to process revised FOI request.
I also hope that I am not waiting in vane for a response from DOIT, otherwise I will make stronger representations, and I have passed my material and questions onto others.
20121125: CASA FOI update, is progressing, albeit with a further extension.
This letter from the Eyre Peninsula Local Government Association was brought to my attention by Google, and we know that Senators are watching see Senate Enquiry, when you read this you will see that government has been taken off guard by the huge escalation in development, presumably caused by the Energy Credits, and no doubt the committment to the Kyoto protocol - money is driving this greed which is compromising our aviation safety, and dare I say health?
20121012: I wrote to the DOIT expressing my concerns regarding the Crookwell Aerodrome and my concerns should the 11 turbines be re-instated and their response is below on the 17th.
20121013: I presented Windfarm Turbines.ppt to the Australian Mooney Pilots Association on the 13 Oct 2012
20121022: I received acknowledgement from the CASA FOI officer of receipt of my FOI request.
Horns Rev Windfarm Wake Plumes Denmark
How far downstream do Windfarm Turbine Wake Plumes extend, as a far as the eye can see. Just look at this photo of the Horns Rev offshore windfarm Denmark for the answer, source In the wake of a wind turbine NOAA news. Photo credit Vattenfall - the Horns Rev wind-farm owner.
This was previously identified in the LEC submissions where SAR has shown these plumes to extend for 10's of kilometers.
This paper Wake effects at Horns Rev and their influence on energy production by Mechali, Barthelmie, Frandsen, Jensen and Rethore, shows that the velocity deficit has be studied up to 5 kms downstream, and yes this means that interacting plumes extend more than 5 kms.
Here is a video of circling the Cullerin Range Windfarm NSW Australia Windmills in the Mist also showing Wake Plumes and blades dangerously extending above the cloud. Imagine that as being smoke with the close proximity of fire-fighting aeroplanes trying to put out fires while operating from Crookwell Aerodrome. Notice that are no recommendations or legislation in Australia to paint the blade tips red like they are in the Horns Rev wind-farm, this is an omission on the part of our authorities
The Gullen Range Aviation Hazard Assessment
Aviation Projects has been engaged again in order to determine operating procedures at Crookwell Aerodrome. in accordance with the court findings I presume; see paragraph 16 of NSWLEC 1444 7 Dec 2009. I believed I heard that a proper study involving CASA was called for during the hearing I attended; so the same consultant will seemingly be informing us how to fly with these turbines. I critised their Aviation Hazard assessment (above), see reference Generic Circuit - my criticism of the Gullen Range WindFarm Aviation Hazard Assessment: Generic Circuit.
Here is another Aviation Assessment that accepts that Structures can be up to 500' without lighting, against at the time current CASA and ICAO recommendations of above 360' formally constituting an obstacle that requires lighting, read and judge for yourself, again no consideration of Wake Plumes. Hart Aviation
Note that the CASA project Assessment of obstacles including wind turbines and exhaust plumes was closed without releasing findings.
The Department of Insfrastructure and Transport (DOIT) releases a white paper to safeguard national airports, however Guidelines D Wind Turbines only affords protection to registered and certified aerodromes, despite this letter from CASA corporate relations.
The LEC determination, Senior Commissioner Tim Moore and Comissioner Judy Fakes.
The exclusion of 11 turbines near Crookwell Aerodrome, an extract from the determination.
December 2009, Australia is the first country to draw Wind Turbine Wake Plume extents to the attention of the aviation community despite both developer's and researcher's awareness of the velocity deficit and the wake turbulence behind turbines well before this timeframe.
Figure 1 - Simulation of Velocity Deficit (in m/s, wind blowing left to right) clearly showing the Wake Plume ref 1
I like to refer to the phenomenon as a Wake Plume because it has both elements of wake tubulence and a plume which tends to be contained, rather than diverging downwind from the turbine.
Around September 2008 I studied Wind Farm Wake Turbulence after I had become aware that Epuron had lodged a development application for the Gullen Range Wind Farm to be situated near the Crookwell Aerodrome, an aerdrome I have used for several training flights, and one which was subjected to my Private Pilot Licence (PPL) flight test.
Crookwell Aerodrome (YCRL) is a 2953' AMSL high elevation airport, comprised of a relatively short 950 metre grass runway that is shielded by a ridge on the western side, which makes takeoffs to the west from runway 27 challenging, and these features make it an interesting training strip for Private and Commerical licences. It is known that at least one Authorised Testing Officer (ATO) uses the strip for the Commercial Pilot Flight Test, and several ATO's have used it for PPL flight tests, and this aerodrome is also very important to the local Crookwell area when it is used for fire fighting operations.
I forwarded my initial findings on Wake Plumes between the 5 and 8 Sep 2008 to the Upper Lachlan Shire Council, NSW Planning, and to the Civil Aviation Safety Authority (CASA), with the view to have the Wake Plumes taken into consideration when reviewing the development application. I subsequently sent them again to the Crookwell Upper Lachlan Shire Council on the 21 Sep 2008.
The Lachlan Upper Shire Council, and NSW Planning authorities sought information from various aviation experts and authorities, but since Crookwell Aerodrome was an Authorised Landing Area (ALA) the official CASA response was Crookwell Airstrip is not covered under CASA's legal jurisdiction and thus has no comments to provide regarding the proposal. This response is a direct citation taken from page 16 of the Director Generals Assessment.
The development was subsequently approved by the NSW Minister for Planning with conditions of approval that included the rejection of 11 wind turbines in order to preserve the aerodrome. Another condition was that lighting is NOT to be installed, other than low intensity lighting, and that the proponent is to engage with CASA to determine the extent of hazard lighting. The conditions also included the removal of the plus or minus 250 metres turbine placement variation from the development application.
The aforementioned approval was granted in the time-frame before three NSW Environment and Planning court hearings could be heard, citing that the development was a Major Project under section 75B(1)(a) of the Environment Planning and Assessment Act 1979.
CASA AC 139-18(0) Obstacle Marking and Lighting for Wind Farms was subsequently withdrawm, and several wind farms now have the priviledge of silent running with no obstacle lighting for pilots at night, despite turbine blade tips being in excess of 110m above the ground level.
To date more than a year later, has been no national aviation authority undergoing studies of the Wake Plume phenomenon. However, CASA informed me on the 7 Dec 2009 that they are now studying it and proposing to draft some legislation that will be available for public comment. This is a first for Australia, and indeed the World Wide Aviation community, and I believe I would not have become aware of the phenomenon had the wind farm development near Crookwell Aerodrome Australia been situated further from the aerodrome and gone unnoticed.
CASA also lists Project AS 06/07 Assessment of obstacles including wind turbines and exhaust plumes, dated 19 Jul 2006, which was recently renamed and is based on CASR Manual of Standards Part 139 - Aerodromes, and CASR Part 173 - Airspace, neither of which afford any protection against turbines unless they are proposed in close proximity to a registered or certified aerodrome and have appropriately operating airspace. At the time of writing (Dec 2009), this legislation has no regard for Wind Turbine Wake Plume, although it has mention of vertical plumes from chimneys. CASA has been working on this project since 2006.
What I believe is that we need legislation that can be used irrespective of the registration status of the aerodromes and irrespective of where a turbine is located, and that legislation needs to be enforceable against a developer, and not necessarily leaving the onus on a pilot or an aerdrome operator.
If you are aware of other runways affected by the threat of wind power generating turbines I would be interested to help. I have appeared as a witness in the NSW Environment and Planning Court to contest the placement of turbines under the potential threat of Aviation Safety represented by these Wake Plumes. I believe the protection can be afforded to the aerodrome operations under due dilligence and duty of care, despite the present lack of the Aviation legal framework, which CASA have recently informed me, it is now in the process of rectfying.
Ralph Holland 2008-2009 - you may contact the author at:
My first defence of the Crookwell Aerodrome was back in Sep 2008 when I summarised some research Turbine Wake Plume and analysed the Epuron Gullen Range - Aviation Hazard Report and criticised it on 11 counts which you can find here in Generic Circuit and forwarded to the planning authorities for their consideration.
I did not realise just how significant these Wake Plumes were in strength and extent when I initially forwarded the papers.
Under increasing awareness brought about by investigations and reports that were submitted to the NSW Environment and Planning Court, I became aware that the Wake Plume extended much further than my original searches had found. I searched for more research papers and was suprised. The data showed that the Wake Plumes do not diverge as people would expect, and that they could extend several kilometres downwind from the turbines, further the plume starts out largely contained by the blade disk behind the turbine and eventually becomes bound between the ground and outer-extremeties of the blade disk, i.e. the plume fills in behind the turbine and the ground and continues downwind for some distance..
This later realisation can be found in my presentation material, which was presented as part of my evidence in the NSW Environment and Planning court. This was an open process, with the proponent, the court and CASA receiving ALL my submissions and then followed by a hearing in court.
I also, just a few months earlier, had the opportunity to fly-by the Cullerin Wind Farm and video Windmills in the Mist while the turbine blades where just protruding above the cloud. This was originally to show the danger of white blades just protruding from white clouds, and to my suprise and delight, I could see down to the ground in streams behind the turbines. This was confirmation that I was on the right track with my investigations into the effects of these wake plumes extending downwind from power generating turbines.
At about this time I fully disclosed the extent to CASA, and forwarded the video evidence and presentation, which was just before I found that the Wake Plumes could extend even further. I performed some more searching after I received the joint expert witness aviation report from the NSW Environment and Planning just before the court proceedings and I found that the plumes can extend more than 15 kilometres over the ideal surface of the ocean. Evidenced in the Syntehtic Aperture Radar (SAR) data obtained from measurements of wind velocities around the Horne Rev offshore windfarm near Denmark. This is not insignificant when you understand just what comprises these Wake Plumes.
My presentation material is in two parts, the first summaries several researcher's measured data, while the second presents a need for a buffer zone around the turbines to prevent their placement interfering with aircraft. This material was presented to court for consideration, and it is a difficult subject since there was currently no national avaiation authority studying the phenomenon, and no aviation legal framework to protect the unregistered Crookwell Aerodrome. My presentation was, however, based on Aviation Safety and appealed to the common law processes of due-dilligence and duty-of-care of the state planners.
The proposed turbine locations near Crookwell Areodrome, can been seen in Google Earth data which I derived from the Gullen Coordinates. I have only included the Northern cluster, and some of the Southern Cluster, because it tooks hours to form this data and I lost time before the court hearing, as well as interest in the remaining turbines because of the extent of the distances in my study. I included the last of which were swept by the buffer zone, and the first of which were completely anhialated. The whole preparation of which was onerous, and performed at my expense, at the expense of several days of the work I do for my living, some sleepless hours, and at times when there was no clear resolution in sight. I am glad that I managed to perservere - there is nothing like an enthusiast doing something they believe is right - for they tend never to give-up. My wife will confirm that I am obsessive - and I believe that personality trait (or defect) assisted in this case.
I was mainly concerned with the turbines in close proximity of the aerodrome, and those that would be intercepted by the CAT-B aircraft circling area, as well as those that later fell within the 15 kilometre buffer zone.
The 15 kilometre buffer was a late submission derived from SAR data for offshore wind farms, where the Wake Plume is propagating over the perfect boundary represented by the sea. I suspect that the wake propagation distance would be less over land, and particularly land with the surface roughness, and with trees etc, as found in the Crookwell area. Because of this uncertaintly I actually called for a scientific study of the Wake Plume, velocity deficit, turbulence and extent by physical measurement of exising wind farms in the area, as well as using scale models in a wind-tunnel taking local terrain roughness into account in my dispositions to the court, and I still believe such a study should be commissioned.
It is my belief that the Wake Plume represents a Safety Hazard to Aviation, in that in parts it represents a void to flight, and in other parts represents a wind-sheer, velocity deficit, and turbulence. I believe that the Wake Plume may result in accidents if pilots happen to fly into it, or across it, and it is with this basis of reasoning that I have been petitioning CASA and intend to pertition ICAO to raise awareness of the dangers. I also have supporting evidence provided by Richard Thompson's personal account of flying into, and luckily out of, such a turbine Wake Plume.
Figure 2 - Aerodrome areas with 11-reject turbines removed.
In my opinion, the rejected 11 turbines are not enough, because there are still several turbines within the CAT-B circling area, and no real allowance has been made for a buffer from these, and other, turbines. There is no buffer protection against the Wake Plumes, as can be seen in the following image, and I am dissappointed that this has caught the aviation community off guard, and that the appropriate authorities have not been able to take the full extent of the Wake Plume into account - Ralph Holland 13 Dec 2009.
I believe that a buffer zone is required around a power generating Wind Turbine to isolate aircraft and pilots from the affects of the Turbine Wake Plumes. Experimental evidence shows that the Wake Plume extends several kilometres downwind from the turbines, and other research shows that the Velocity Deficit effect is strengthened behind Wind Turbine clusters. In my opinion, the remaining turbines will present their Wake Plume towards the Crookwell Aerodrome under South-Westerly wind conditions.
CASA has indicated that it is studying and proposing to draft legislation and instrumentation for these obstructions, and it is probable that such legislation will determine safe and reasonable distances, which may lead to the imposition of Restricted or Danger Areas - no fly zones - around wind turbines.
With the remaining turbines still relatively close to Crookwell Aerodrome, the aerodrome is still under threat of closure. Subsequent CASA legislation runs the risk of closing the aerodrome after the Wind Farm development approval process is completed.
It is also probable that the requirements for markings and lighting will be more inline with the European standards of orange or red striped-blades and nacelle obstacle lights. Again it is probable that this legislation will be drafted after the development approval resulting in yet another unsafe situation, as we have with the Lake George Capital Wind Farm turbines that are unlit, with their blades too poking out of clouds.
These turbine hazard findings will be required to be promulgated through pilot education schemes to reinforce that Wind Turbines and Wake Plumes are to be avoided, and I await the new CASA legislation and monitor their projects, but it may be too late for Crookwell Aerodrome.