CN103852119A - Continuous wind tunnel compressor inlet flow measurement method - Google Patents

Abstract

The invention relates to a continuous wind tunnel compressor inlet flow measurement method. The continuous wind tunnel compressor inlet flow measurement method is used for solving the problems that flow in a pipeline in front of a compressor is non-uniform and unstable, the total pressure and static pressure of cross sections are measured by using Pitot-static probes, the speed is obtained by a Bernoulli equation, and thus, the fluctuation of calculated volume flow of the cross sections is too large, so that measured error bands of surge points and surge borders are too wide and volume flow determined during actual operation is not accurate enough. The method provided by the invention has the advantages that the inlet flow of the compressor is measured and calculated accurately, the surge borders can be determined accurately, and whether the compressor is in surging or not is accurately judged.

Description

A kind of continuous wind tunnel suction port of compressor flow-measuring method

Technical field

The present invention relates to one and relate to axial compressor inlet flow rate measuring method, be particularly useful for being arranged on the inlet flow rate measurement of transonic wind tunnel loop Axial-Flow compressor.

Background technology

Axial compressor is for high-speed wind tunnel loop, for test chamber provides the pressure ratio of continous-stable, makes test section set up the air velocity distribution of stable and uniform, for dummy vehicle experiment provides guarantee.But compressor is an equipment that has own unique operation characteristic.Fig. 1 is one group of general characteristic curve synoptic diagram of compressor.In figure, dotted line represents the compressor performance curves under a certain given rotating speed, different stator blades angle β, i.e. pressure ratio (outlet stagnation pressure/import stagnation pressure)～flow curve.After compressor operating, turn down gradually outlet valve (be grid refer to or bypass valve) in wind-tunnel under given rotating speed, a certain stator blade angle time, will make compressor operation parameters move to upper left side along the performance curve at this stator blade angle, in the time of compressor generation surge, find a pumping point.Pumping point under given rotating speed, different stator blades angle is linked up smoothly, is exactly the surge boundary line (solid line in figure) of this compressor under this given rotating speed.When compressor operating, working point must be in the lower right of this surge boundary line (solid line), and never allows it to go to the upper left side of surge line.If working conditions of compressor point is gone to surge boundary line upper left side accidentally, can cause compressor to enter surging condition, serious meeting makes the device such as rotor, stator stand varying stress and rupture, interstage pressure is not normal to be caused and judder causes sealing bearing bush and bearing damage, even may damage at short notice compressor, the blade of breakdown also may be blown to (with reference to figure 2) in wind-tunnel loop, cause the breaking-up of wind tunnel component and measuring equipment, even jeopardize staff's life, cause serious consequence.Therefore, the Accurate Determining of stall margin and prevention compressor enter the basis that surging condition is compressor and wind-tunnel safe and stable operation.And can suction port of compressor flow Measurement accuracy be the key that can compressor surge border accurately definite.

Conventionally the pipe network system of compressor application is mostly incompressible stream mode, so tradition or conventional way are to think that the pipeline at suction port of compressor place is incompressible flow, therefore available pitot static tube (Pitot-static probe) is measured after stagnation pressure, differential static pressure, obtain speed by Bernoulli equation, then calculate flow.

When NF-6 supercharging continuous wind tunnel starts to carry out stall margin mensuration, (in July, 2007 and Dec) is exactly to measure in this way suction port of compressor flow, the first downstream, round corner section (i.e. the 3rd diffuser before suction port of compressor at that time, referring to Fig. 2) three standard wind speed pipes have been installed, after measuring total differential static pressure, calculate flow velocity by Bernoulli equation, and from three speed, select the averaging as the average velocity in this cross section of two gap minimums, be then multiplied by cross-sectional area and obtain volumetric flow rate.Mobile inhomogeneous due on this xsect, unstable, volumetric flow rate fluctuation under the same trystate that this measuring method causes providing is very large, determine that by this measuring method pumping point and stall margin are with wider error band, in application process, use too this method calculated flow rate, result causes data point that wind-tunnel supervisory system records regularly, cross randomly the stall margin setting in advance, make to be difficult to judge to whether entering surging condition, or cause erroneous judgement, the quick valve of anti-asthma bypass is frequently opened, cause wind-tunnel normally to work.So when compressor is installed on high-speed wind tunnel loop when driving air-flow to set up test section flow field, this flow-measuring method is not very suitable, need to seek more accurate flow measurement or computing method.

Mobile inhomogeneous due in the pipeline of compressor front, unstable, these for cross section pitot static tube (Pitot-static probe) measure stagnation pressure, static pressure, obtain speed by Bernoulli equation, the xsect volumetric flow rate fluctuation calculating is thus too large, thereby cause the error band of the pumping point that records and stall margin too wide, and also not accurate enough by the definite volumetric flow rate of this measuring method in actual motion, namely making monitoring benchmark with an inaccurate stall margin, judge whether fail to measure the corresponding operating point of flow value accurately for one enters surge, when this probably causes operation also not enter surging condition, system is but frequently reported to the police, and fail to perceive and cause serious consequence while really entering surge, thereby wind-tunnel cannot normally be worked.

Summary of the invention

The technical matters solving

For fear of the deficiencies in the prior art part, the present invention proposes a kind of continuous wind tunnel suction port of compressor flow-measuring method, the method that provides a Measurement accuracy and calculating suction port of compressor flow, makes stall margin be able to Accurate Determining, and whether compressor enters surge and be able to accurate judgement.

Technical scheme

A kind of continuous wind tunnel suction port of compressor flow-measuring method, is characterized in that being divided into bypass valve and closes and two kinds of situations of bypass valve unlatching, and measuring process is as follows:

Situation 1: in the time that bypass valve cuts out, continuous wind tunnel suction port of compressor volume flow measurement step is as follows:

Step 1: the mass rate that must enter suction port of compressor according to continuity equation equals the mass rate that test section flows out, test section mass rate:

$\stackrel{\·}{m}=\mathrm{\Γ}\frac{p_0}{\sqrt{T_0}}\mathrm{Aq}\left(M_{\∞}\right)$

Described $\mathrm{\Γ}=\sqrt{\frac{\mathrm{\γ}}{R}{\left(\frac{2}{\mathrm{\γ}+1}\right)}^{\frac{\mathrm{\γ}+1}{\mathrm{\γ}-1}}},$

Described $M_{\∞}={\left\{\frac{2}{\mathrm{\γ}-1}\right[{\left(\frac{p_0}{p_{\∞}}\right)}^{(\mathrm{\γ}-1)/\mathrm{\γ}}-1\left]\right\}}^{1/2},$

Described $q\left(M_{\∞}\right)=M_{\∞}{\left[\frac{2}{\mathrm{\γ}+1}(1+\frac{\mathrm{\γ}-1}{2}{M}_{\∞}^2)\right]}^{-\frac{\mathrm{\γ}+1}{2(\mathrm{\γ}-1)}},$

Wherein: p ₀for stable section stagnation pressure, T ₀for stable section stagnation temperature, Γ is a combination parameter of gas law constant composition, M _∞for test section incoming flow Mach number, p _∞for test section incoming flow static pressure, q (M _∞) be flow function, A is test section cross-sectional area, and R is gas law constant, and for air, its value is 287J (molK), and γ is specific heats of gases ratios, for air, its value is 1.4;

Step 2: the volumetric flow rate of suction port of compressor

wherein: ρ _{c, in}for the gas density at suction port of compressor place,

for suction port of compressor air-flow stagnation pressure,

for suction port of compressor air-flow stagnation temperature;

Situation 2: in the time that bypass valve is opened, flow measurement step in continuous wind tunnel suction port of compressor is as follows:

Step 1: the gas mass flow by anti-asthma bypass is

test section mass rate, the flow that enters compressor is

wherein:

ρ _bpfor the gas density in anti-asthma bypass, V _bpfor the gas velocity of anti-asthma bypass, A _bpfor the cross-section of pipeline of anti-asthma bypass amasss;

Described

wherein: p _{0, bp}for the air-flow stagnation pressure in anti-asthma bypass duct, T _{0, bp}for the air-flow stagnation temperature in anti-asthma bypass duct;

Described

wherein: p _{0, bp}poor for the measured air-flow stagnation pressure of pitot tube in anti-asthma bypass duct and static pressure;

Step 2: the volumetric flow rate of suction port of compressor is:

Beneficial effect

A kind of continuous wind tunnel suction port of compressor flow-measuring method that the present invention proposes, solve mobile inhomogeneous, unstable due in the pipeline of compressor front, these for cross section pitot static tube (Pitot-static probe) measure stagnation pressure, static pressure, obtain speed by Bernoulli equation, the xsect volumetric flow rate fluctuation calculating is thus too large, thereby cause the error band of the pumping point that records and stall margin too wide, and in actual motion by the definite volumetric flow rate of this measuring method also not accurate enough problem.The present invention provides a Measurement accuracy and calculates the method for suction port of compressor flow, makes stall margin be able to Accurate Determining, and whether compressor enters surge and be able to accurate judgement.

Brief description of the drawings

Fig. 1: axial compressor general characteristic curve

Fig. 2: NF-6 wind tunnel principle figure

Fig. 3: the pumping point test data of compressor rotary speed n=1600rpm

Fig. 4: the pumping point test data of compressor rotary speed n=2100rpm

Fig. 5: compressor surge border

1-compressor, 2-test chamber, 3-grid refer to, 4-anti-asthma bypass quick valve, pumping point test data when 5-compressor is 40 ° at 1600rpm stator blade angle, pumping point test data when 6-compressor is 50 ° at 1600rpm stator blade angle, pumping point test data when 7-compressor is 60 ° at 1600rpm stator blade angle, pumping point test data when 8-compressor is 70 ° at 1600rpm stator blade angle, pumping point test data when 9-compressor is 80 ° at 1600rpm stator blade angle, pumping point test data when 10-compressor is 55 ° at 2100rpm stator blade angle, pumping point test data when 11-compressor is 65 ° at 2100rpm stator blade angle, pumping point test data when 12-compressor is 75 ° at 2100rpm stator blade angle, the stall margin of 13-compressor in the time of 1600rpm, the stall margin of 14-compressor in the time of 2100rpm, the stall margin of 15-compressor in the time of 2524rpm, the stall margin of 16-compressor in the time of 2900rpm, the stall margin of 17-compressor in the time of 3000rpm, the stall margin of 18-compressor in the time of 3200rpm.

Embodiment

Now in conjunction with the embodiments, the invention will be further described for accompanying drawing:

The embodiment of the present invention:

According to the principle of mass conservation, a ducted mass rate remains unchanged along pipeline.In the time that bypass valve (bypass valves) cuts out, the mass rate that flows through test chamber should equal to flow into the mass rate (referring to Fig. 3) of suction port of compressor so.And in general, a qualified wind-tunnel, its test section flow field is generally more stable, Mach number control accuracy is higher, because its mass rate is the function of total pressure, stagnation temperature, test section Mach number, thereby test section flow is more stable, thus can be according to test section mass flow calculation suction port of compressor volumetric flow rate for the principle of mass conservation.

(1) bypass valve cuts out situation

In the time that bypass valve cuts out, according to continuity equation, the mass rate that enters suction port of compressor should equal the mass rate (referring to Fig. 3) that experimental section flows out.And experimental section mass rate should be

$\stackrel{\·}{m}=\mathrm{\Γ}\frac{p_0}{\sqrt{T_0}}\mathrm{Aq}\left(M_{\∞}\right)---\left(1\right)$

Wherein, p ₀, T ₀for stable section stagnation pressure and stagnation temperature, Γ is a combination parameter of gas law constant composition

$\mathrm{\Γ}=\sqrt{\frac{\mathrm{\γ}}{R}{\left(\frac{2}{\mathrm{\γ}+1}\right)}^{\frac{\mathrm{\γ}+1}{\mathrm{\γ}-1}}}$

M _∞for test section incoming flow Mach number, can be calculated by isentropic relation by stable section stagnation pressure/experimental section static pressure ratio,

$M_{\∞}={\left\{\frac{2}{\mathrm{\γ}-1}\right[{\left(\frac{p_0}{p_{\∞}}\right)}^{(\mathrm{\γ}-1)/\mathrm{\γ}}-1\left]\right\}}^{1/2}---\left(2\right)$

Obtain M _∞after can be by flow function q (M _∞) formula calculates q (M _∞) value

$q\left(M_{\∞}\right)=M_{\∞}{\left[\frac{2}{\mathrm{\γ}+1}(1+\frac{\mathrm{\γ}-1}{2}{M}_{\∞}^2)\right]}^{-\frac{\mathrm{\γ}+1}{2(\mathrm{\γ}-1)}}---\left(3\right)$

Calculate again experimental section area A=height × wide, just can calculate experimental section mass rate by (1)

?

$\stackrel{\·}{m}=\sqrt{\frac{\mathrm{\γ}}{R}{\left(\frac{2}{\mathrm{\γ}+1}\right)}^{\frac{\mathrm{\γ}+1}{\mathrm{\γ}-1}}}\frac{p_0}{\sqrt{T_0}}A{M}_{\∞}{\left[\frac{2}{\mathrm{\γ}+1}(1+\frac{\mathrm{\γ}-1}{2}{M}_{\∞}^2)\right]}^{-\frac{\mathrm{\γ}+1}{2(\mathrm{\γ}-1)}}---\left(4\right)$

namely enter the mass rate of compressor.

If record suction port of compressor stagnation pressure before suction port of compressor

with entrance stagnation temperature

(subscript c represents compressor compressor, and in represents suction port of compressor inlet), because this section of flow velocity is lower, can think can not baric flow, its stagnation density

little with quiet density difference, think that density is constant, can be obtained by state equation the density p at this place _{c, in}

${\mathrm{\ρ}}_{c,\mathrm{in}}=\frac{p_{c,\mathrm{in}}^0}{{\mathrm{RT}}_{c,\mathrm{in}}^0}---\left(5\right)$

Like this, the volumetric flow rate that enters compressor is

${\stackrel{\·}{v}}_{c,\mathrm{in}}=\stackrel{\·}{m}/{\mathrm{\ρ}}_{c,\mathrm{in}}---\left(6\right)$

(2) bypass valve is opened situation

If bypass valve is opened, some flow, not from experimental section process, enters compressor but guide to suction port of compressor by bypass, establishes by the mass rate of bypass to be

(subscript bp represents bypass, i.e. bypass), the flow that enters compressor is (referring to Fig. 3), the volumetric flow rate that enters so compressor is

${\stackrel{\·}{v}}_{\mathrm{cin}}=(\stackrel{\·}{m}+{\stackrel{\·}{m}}_{\mathrm{bp}})/{\mathrm{\ρ}}_{c,\mathrm{in}}---\left(7\right)$

Gas velocity in bypass duct is measured always quiet, pressure reduction by the pitot static tube that is arranged on there, calculates by incompressible flow Bernoulli equation

$V_{\mathrm{bp}}=\sqrt{\frac{2(p_{0,\mathrm{bp}}-p_{\mathrm{bp}})}{{\mathrm{\ρ}}_{\mathrm{bp}}}}---\left(8\right)$

Density p wherein _bpby the bypass stagnation pressure p measuring that pops one's head in of stagnation pressure in shunt valve _{0, bp}with stagnation temperature T _{0, bp}calculate

${\mathrm{\ρ}}_{\mathrm{bp}}=\frac{p_{0,\mathrm{bp}}}{R{T}_{0,\mathrm{bp}}}---\left(9\right)$

Finally can obtain the mass rate of bypass

${\stackrel{\·}{m}}_{\mathrm{bp}}={\mathrm{\ρ}}_{\mathrm{bp}}{V}_{\mathrm{bp}}{A}_{\mathrm{bp}}---\left(10\right)$

Wherein, A _bpfor the cross-sectional area of bypass duct.

The suction port of compressor flow of the NF-6 wind-tunnel to Northwestern Polytechnical University is implemented to measure.This wind-tunnel is a continous way transonic wind tunnel, and power source is an Axial Flow Compressor.

Concrete steps are as follows:

Step (1): under each running status, available total pressure transmitter records wind-tunnel stable section stagnation pressure p ₀, record stable section stagnation temperature T with stagnation temperature transmitter ₀, in the flow field debug phase (comprising definite stall margin) of not yet carrying out before the survey of school, flow field, get sidewall the first pressure tap force value (ternary test section is got in constant pressure strong) for p for binary test section _∞, calculate incoming flow Mach number M by formula (2) _∞, can calculate by formula (4) mass rate that flows through test section

; When wind-tunnel builds up, completed after the survey of school, flow field, with surveying definite M in school, flow field _∞and reference point (binary test section is got sidewall the first pressure tap, and ternary test section is got in chamber) Mach number M _crelation, from target incoming flow Mach number M _∞obtain corresponding M _c, by regulating compressor rotary speed and stator blade angle to obtain required M with automatic control mode _c, M _cwith p ₀, p _c(binary test section p _cget sidewall the first pressure tap force value, ternary test section p _cget that to stay constant pressure strong) relation object be similar to total static pressure relation of equation (2),

$M_c={\left\{\frac{2}{\mathrm{\γ}-1}\right[{\left(\frac{p_0}{p_c}\right)}^{(\mathrm{\γ}-1)/\mathrm{\γ}}-1\left]\right\}}^{1/2}$

After flow field is stable, test section Mach number reaches desired value M _∞, use M _∞can calculate test section mass rate by formula (4)

Step (2): if bypass valve in open mode, also needs according to bypass stagnation pressure p _{0, bp}, stagnation temperature T _{0, bp}, bypass static pressure p _bp, by formula (8), (9), (10) can calculate the mass rate that flows through bypass

Step (3): according to suction port of compressor stagnation pressure

entrance stagnation temperature

can be tried to achieve the density p at suction port of compressor place by formula (5) _{c, in}.

Step (4): be in closing or opening according to bypass valve, selecting formula (6) or formula (7) to calculate suction port of compressor volumetric flow rate

In NF-6 supercharging continous way transonic wind tunnel compressor surging test, calculate suction port of compressor volumetric flow rate with said method, obtained pumping point, stall margin accurately.Fig. 3 is under rotation speed n=1600rpm, β=40 °, 5 stator blade angles, and 50 °, 60 °, 70 °, trajectory is breathed heavily in 80 ° force, and the left end point of each trajectory is pumping point.The pumping point line at each stator blade angle is the surge boundary line under this rotating speed.Fig. 4 is n=2011rpm ,=55 ° respectively of β, 65 °, 75 ° force the process of breathing heavily.

Under other rotating speed, pumping point, surge boundary line all can similar approach obtain.Fig. 5 has provided by the definite n=1600 of said method calculating suction port of compressor volumetric flow rate, the surge boundary line under the each rotating speed of 2100,2524,2900,3000,3200rpm.

Claims (1)

1. a continuous wind tunnel suction port of compressor flow-measuring method, is characterized in that being divided into that bypass valve cuts out and bypass valve

Open two kinds of situations, measuring process is as follows:

Situation 1: in the time that bypass valve cuts out, continuous wind tunnel suction port of compressor volume flow measurement step is as follows:

Step 1: the mass rate that must enter suction port of compressor according to continuity equation equals the mass rate that test section flows out, test section mass rate:

$\stackrel{\·}{m}=\mathrm{\Γ}\frac{p_0}{\sqrt{T_0}}\mathrm{Aq}\left(M_{\∞}\right)$

Described $\mathrm{\Γ}=\sqrt{\frac{\mathrm{\γ}}{R}{\left(\frac{2}{\mathrm{\γ}+1}\right)}^{\frac{\mathrm{\γ}+1}{\mathrm{\γ}-1}}},$

Described $M_{\∞}={\left\{\frac{2}{\mathrm{\γ}-1}\right[{\left(\frac{p_0}{p_{\∞}}\right)}^{(\mathrm{\γ}-1)/\mathrm{\γ}}-1\left]\right\}}^{1/2},$

Described $q\left(M_{\∞}\right)=M_{\∞}{\left[\frac{2}{\mathrm{\γ}+1}(1+\frac{\mathrm{\γ}-1}{2}{M}_{\∞}^2)\right]}^{-\frac{\mathrm{\γ}+1}{2(\mathrm{\γ}-1)}},$

Wherein: p ₀for stable section stagnation pressure, T ₀for stable section stagnation temperature, Γ is a combination parameter of gas law constant composition, M _∞for test section incoming flow Mach number, p _∞for test section incoming flow static pressure, q (M _∞) be flow function, A is test section cross-sectional area, and R is gas law constant, and for air, its value is 287J (molK), and γ is specific heats of gases ratios, for air, its value is 1.4;

Step 2: the volumetric flow rate of suction port of compressor

wherein: ρ _{c, in}for the gas density at suction port of compressor place,

for suction port of compressor air-flow stagnation pressure,

for suction port of compressor air-flow stagnation temperature;

Situation 2: in the time that bypass valve is opened, flow measurement step in continuous wind tunnel suction port of compressor is as follows:

Step 1: the gas mass flow by anti-asthma bypass is test section mass rate, the flow that enters compressor is wherein:

ρ _bpfor the gas density in anti-asthma bypass, V _bpfor the gas velocity of anti-asthma bypass, A _bpfor the cross-section of pipeline of anti-asthma bypass amasss;

Described

wherein: p _{0, bp}for the air-flow stagnation pressure in anti-asthma bypass duct, T _{0, bp}for the air-flow stagnation temperature in anti-asthma bypass duct;

Described

wherein: p _{0, bp}poor for the measured air-flow stagnation pressure of pitot tube in anti-asthma bypass duct and static pressure;

Step 2: the volumetric flow rate of suction port of compressor is:

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